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| author |   Vratko Polak <vrpolak@cisco.com> | 2024-08-28 10:40:08 +0200 |
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| committer | Vratko Polak <vrpolak@cisco.com> | 2024-08-28 10:40:08 +0200 |
| commit | f5a19af10a4a79b5cb096c46311ebb6ca4129274 (patch) | |
| tree | 27beea72d26ee24b7418a766ff02da2a33f6a266 /docs/ietf/draft-ietf-bmwg-mlrsearch-07.txt | |
| parent | 6e48104f915be4cd7d6246afe7b32bf7a9f74787 (diff) | |
feat(ietf): Prepare for MLRsearch draft-08
Change-Id: I882e7068b1dad4547356a497353abc9dc30abffd
Signed-off-by: Vratko Polak <vrpolak@cisco.com>
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diff --git a/docs/ietf/draft-ietf-bmwg-mlrsearch-07.txt b/docs/ietf/draft-ietf-bmwg-mlrsearch-07.txt deleted file mode 100644 index c5c94410a8..0000000000 --- a/docs/ietf/draft-ietf-bmwg-mlrsearch-07.txt +++ /dev/null @@ -1,2800 +0,0 @@ - - - - -Benchmarking Working Group M. Konstantynowicz -Internet-Draft V. Polak -Intended status: Informational Cisco Systems -Expires: 18 January 2025 18 July 2024 - - - Multiple Loss Ratio Search - draft-ietf-bmwg-mlrsearch-07 - -Abstract - - This document proposes extensions to [RFC2544] throughput search by - defining a new methodology called Multiple Loss Ratio search - (MLRsearch). MLRsearch aims to minimize search duration, support - multiple loss ratio searches, and enhance result repeatability and - comparability. - - The primary reason for extending [RFC2544] is to address the - challenges and requirements presented by the evaluation and testing - of software-based networking systems' data planes. - - To give users more freedom, MLRsearch provides additional - configuration options such as allowing multiple short trials per load - instead of one large trial, tolerating a certain percentage of trial - results with higher loss, and supporting the search for multiple - goals with varying loss ratios. - -Status of This Memo - - This Internet-Draft is submitted in full conformance with the - provisions of BCP 78 and BCP 79. - - Internet-Drafts are working documents of the Internet Engineering - Task Force (IETF). Note that other groups may also distribute - working documents as Internet-Drafts. The list of current Internet- - Drafts is at https://datatracker.ietf.org/drafts/current/. - - Internet-Drafts are draft documents valid for a maximum of six months - and may be updated, replaced, or obsoleted by other documents at any - time. It is inappropriate to use Internet-Drafts as reference - material or to cite them other than as "work in progress." - - This Internet-Draft will expire on 18 January 2025. - -Copyright Notice - - Copyright (c) 2024 IETF Trust and the persons identified as the - document authors. All rights reserved. - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 1] - -Internet-Draft MLRsearch July 2024 - - - This document is subject to BCP 78 and the IETF Trust's Legal - Provisions Relating to IETF Documents (https://trustee.ietf.org/ - license-info) in effect on the date of publication of this document. - Please review these documents carefully, as they describe your rights - and restrictions with respect to this document. Code Components - extracted from this document must include Revised BSD License text as - described in Section 4.e of the Trust Legal Provisions and are - provided without warranty as described in the Revised BSD License. - -Table of Contents - - 1. Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . 4 - 2. Identified Problems . . . . . . . . . . . . . . . . . . . . . 5 - 2.1. Long Search Duration . . . . . . . . . . . . . . . . . . 5 - 2.2. DUT in SUT . . . . . . . . . . . . . . . . . . . . . . . 6 - 2.3. Repeatability and Comparability . . . . . . . . . . . . . 8 - 2.4. Throughput with Non-Zero Loss . . . . . . . . . . . . . . 8 - 2.5. Inconsistent Trial Results . . . . . . . . . . . . . . . 9 - 3. MLRsearch Specification . . . . . . . . . . . . . . . . . . . 10 - 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 10 - 3.2. Measurement Quantities . . . . . . . . . . . . . . . . . 11 - 3.3. Existing Terms . . . . . . . . . . . . . . . . . . . . . 12 - 3.3.1. SUT . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 3.3.2. DUT . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 3.3.3. Trial . . . . . . . . . . . . . . . . . . . . . . . . 12 - 3.4. Trial Terms . . . . . . . . . . . . . . . . . . . . . . . 13 - 3.4.1. Trial Duration . . . . . . . . . . . . . . . . . . . 14 - 3.4.2. Trial Load . . . . . . . . . . . . . . . . . . . . . 14 - 3.4.3. Trial Input . . . . . . . . . . . . . . . . . . . . . 15 - 3.4.4. Traffic Profile . . . . . . . . . . . . . . . . . . . 15 - 3.4.5. Trial Forwarding Ratio . . . . . . . . . . . . . . . 16 - 3.4.6. Trial Loss Ratio . . . . . . . . . . . . . . . . . . 16 - 3.4.7. Trial Forwarding Rate . . . . . . . . . . . . . . . . 17 - 3.4.8. Trial Effective Duration . . . . . . . . . . . . . . 17 - 3.4.9. Trial Output . . . . . . . . . . . . . . . . . . . . 18 - 3.4.10. Trial Result . . . . . . . . . . . . . . . . . . . . 18 - 3.5. Goal Terms . . . . . . . . . . . . . . . . . . . . . . . 19 - 3.5.1. Goal Final Trial Duration . . . . . . . . . . . . . . 19 - 3.5.2. Goal Duration Sum . . . . . . . . . . . . . . . . . . 19 - 3.5.3. Goal Loss Ratio . . . . . . . . . . . . . . . . . . . 20 - 3.5.4. Goal Exceed Ratio . . . . . . . . . . . . . . . . . . 20 - 3.5.5. Goal Width . . . . . . . . . . . . . . . . . . . . . 21 - 3.5.6. Search Goal . . . . . . . . . . . . . . . . . . . . . 21 - 3.5.7. Controller Input . . . . . . . . . . . . . . . . . . 22 - 3.6. Search Goal Examples . . . . . . . . . . . . . . . . . . 23 - 3.6.1. RFC2544 Goal . . . . . . . . . . . . . . . . . . . . 23 - 3.6.2. TST009 Goal . . . . . . . . . . . . . . . . . . . . . 24 - 3.7. Result Terms . . . . . . . . . . . . . . . . . . . . . . 24 - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 2] - -Internet-Draft MLRsearch July 2024 - - - 3.7.1. Relevant Upper Bound . . . . . . . . . . . . . . . . 25 - 3.7.2. Relevant Lower Bound . . . . . . . . . . . . . . . . 25 - 3.7.3. Conditional Throughput . . . . . . . . . . . . . . . 26 - 3.7.4. Goal Result . . . . . . . . . . . . . . . . . . . . . 26 - 3.7.5. Search Result . . . . . . . . . . . . . . . . . . . . 27 - 3.7.6. Controller Output . . . . . . . . . . . . . . . . . . 27 - 3.8. MLRsearch Architecture . . . . . . . . . . . . . . . . . 28 - 3.8.1. Measurer . . . . . . . . . . . . . . . . . . . . . . 28 - 3.8.2. Controller . . . . . . . . . . . . . . . . . . . . . 29 - 3.8.3. Manager . . . . . . . . . . . . . . . . . . . . . . . 29 - 3.9. Implementation Compliance . . . . . . . . . . . . . . . . 30 - 4. Additional Considerations . . . . . . . . . . . . . . . . . . 30 - 4.1. MLRsearch Versions . . . . . . . . . . . . . . . . . . . 31 - 4.2. Stopping Conditions . . . . . . . . . . . . . . . . . . . 31 - 4.3. Load Classification . . . . . . . . . . . . . . . . . . . 32 - 4.4. Loss Ratios . . . . . . . . . . . . . . . . . . . . . . . 32 - 4.5. Loss Inversion . . . . . . . . . . . . . . . . . . . . . 33 - 4.6. Exceed Ratio . . . . . . . . . . . . . . . . . . . . . . 34 - 4.7. Duration Sum . . . . . . . . . . . . . . . . . . . . . . 34 - 4.8. Short Trials . . . . . . . . . . . . . . . . . . . . . . 35 - 4.9. Throughput . . . . . . . . . . . . . . . . . . . . . . . 35 - 4.10. Search Time . . . . . . . . . . . . . . . . . . . . . . . 37 - 4.11. RFC2544 Compliance . . . . . . . . . . . . . . . . . . . 38 - 5. Logic of Load Classification . . . . . . . . . . . . . . . . 38 - 5.1. Introductory Remarks . . . . . . . . . . . . . . . . . . 38 - 5.2. Performance Spectrum . . . . . . . . . . . . . . . . . . 38 - 5.2.1. First Example . . . . . . . . . . . . . . . . . . . . 39 - 5.2.2. Second Example . . . . . . . . . . . . . . . . . . . 40 - 5.2.3. Third Example . . . . . . . . . . . . . . . . . . . . 40 - 5.2.4. Summary . . . . . . . . . . . . . . . . . . . . . . . 40 - 5.3. Trials with Single Duration . . . . . . . . . . . . . . . 40 - 5.4. Trials with Short Duration . . . . . . . . . . . . . . . 42 - 5.4.1. Scenarios . . . . . . . . . . . . . . . . . . . . . . 42 - 5.4.2. Classification Logic . . . . . . . . . . . . . . . . 43 - 5.5. Trials with Longer Duration . . . . . . . . . . . . . . . 45 - 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45 - 7. Security Considerations . . . . . . . . . . . . . . . . . . . 45 - 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 46 - 9. Appendix A: Load Classification . . . . . . . . . . . . . . . 46 - 10. Appendix B: Conditional Throughput . . . . . . . . . . . . . 47 - 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 49 - 11.1. Normative References . . . . . . . . . . . . . . . . . . 49 - 11.2. Informative References . . . . . . . . . . . . . . . . . 49 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49 - - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 3] - -Internet-Draft MLRsearch July 2024 - - -1. Purpose and Scope - - The purpose of this document is to describe Multiple Loss Ratio - search (MLRsearch), a data plane throughput search methodology - optimized for software networking DUTs. - - Applying vanilla [RFC2544] throughput bisection to software DUTs - results in several problems: - - * Binary search takes too long as most trials are done far from the - eventually found throughput. - - * The required final trial duration and pauses between trials - prolong the overall search duration. - - * Software DUTs show noisy trial results, leading to a big spread of - possible discovered throughput values. - - * Throughput requires a loss of exactly zero frames, but the - industry frequently allows for small but non-zero losses. - - * The definition of throughput is not clear when trial results are - inconsistent. - - To address the problems mentioned above, the MLRsearch test - methodology specification employs the following enhancements: - - * Allow multiple short trials instead of one big trial per load. - - - Optionally, tolerate a percentage of trial results with higher - loss. - - * Allow searching for multiple Search Goals, with differing loss - ratios. - - - Any trial result can affect each Search Goal in principle. - - * Insert multiple coarse targets for each Search Goal, earlier ones - need to spend less time on trials. - - - Earlier targets also aim for lesser precision. - - - Use Forwarding Rate (FR) at maximum offered load [RFC2285] - (section 3.6.2) to initialize the initial targets. - - * Take care when dealing with inconsistent trial results. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 4] - -Internet-Draft MLRsearch July 2024 - - - - Reported throughput is smaller than the smallest load with high - loss. - - - Smaller load candidates are measured first. - - * Apply several load selection heuristics to save even more time by - trying hard to avoid unnecessarily narrow bounds. - - Some of these enhancements are formalized as MLRsearch specification, - the remaining enhancements are treated as implementation details, - thus achieving high comparability without limiting future - improvements. - - MLRsearch configuration options are flexible enough to support both - conservative settings and aggressive settings. The conservative - settings lead to results unconditionally compliant with [RFC2544], - but longer search duration and worse repeatability. Conversely, - aggressive settings lead to shorter search duration and better - repeatability, but the results are not compliant with [RFC2544]. - - No part of [RFC2544] is intended to be obsoleted by this document. - -2. Identified Problems - - This chapter describes the problems affecting usability of various - performance testing methodologies, mainly a binary search for - [RFC2544] unconditionally compliant throughput. - -2.1. Long Search Duration - - The emergence of software DUTs, with frequent software updates and a - number of different frame processing modes and configurations, has - increased both the number of performance tests required to verify the - DUT update and the frequency of running those tests. This makes the - overall test execution time even more important than before. - - The current [RFC2544] throughput definition restricts the potential - for time-efficiency improvements. A more generalized throughput - concept could enable further enhancements while maintaining the - precision of simpler methods. - - The bisection method, when unconditionally compliant with [RFC2544], - is excessively slow. This is because a significant amount of time is - spent on trials with loads that, in retrospect, are far from the - final determined throughput. - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 5] - -Internet-Draft MLRsearch July 2024 - - - [RFC2544] does not specify any stopping condition for throughput - search, so users already have an access to a limited trade-off - between search duration and achieved precision. However, each full - 60-second trials doubles the precision, so not many trials can be - removed without a substantial loss of precision. - -2.2. DUT in SUT - - [RFC2285] defines: - DUT as - The network forwarding device to which - stimulus is offered and response measured [RFC2285] (section 3.1.1). - - SUT as - The collective set of network devices to which stimulus is - offered as a single entity and response measured [RFC2285] (section - 3.1.2). - - [RFC2544] specifies a test setup with an external tester stimulating - the networking system, treating it either as a single DUT, or as a - system of devices, an SUT. - - In the case of software networking, the SUT consists of not only the - DUT as a software program processing frames, but also of server - hardware and operating system functions, with that server hardware - resources shared across all programs including the operating system. - - Given that the SUT is a shared multi-tenant environment encompassing - the DUT and other components, the DUT might inadvertently experience - interference from the operating system or other software operating on - the same server. - - Some of this interference can be mitigated. For instance, pinning - DUT program threads to specific CPU cores and isolating those cores - can prevent context switching. - - Despite taking all feasible precautions, some adverse effects may - still impact the DUT's network performance. In this document, these - effects are collectively referred to as SUT noise, even if the - effects are not as unpredictable as what other engineering - disciplines call noise. - - DUT can also exhibit fluctuating performance itself, for reasons not - related to the rest of SUT. For example due to pauses in execution - as needed for internal stateful processing. In many cases this may - be an expected per-design behavior, as it would be observable even in - a hypothetical scenario where all sources of SUT noise are - eliminated. Such behavior affects trial results in a way similar to - SUT noise. As the two phenomenons are hard to distinguish, in this - document the term 'noise' is used to encompass both the internal - performance fluctuations of the DUT and the genuine noise of the SUT. - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 6] - -Internet-Draft MLRsearch July 2024 - - - A simple model of SUT performance consists of an idealized noiseless - performance, and additional noise effects. For a specific SUT, the - noiseless performance is assumed to be constant, with all observed - performance variations being attributed to noise. The impact of the - noise can vary in time, sometimes wildly, even within a single trial. - The noise can sometimes be negligible, but frequently it lowers the - observed SUT performance as observed in trial results. - - In this model, SUT does not have a single performance value, it has a - spectrum. One end of the spectrum is the idealized noiseless - performance value, the other end can be called a noiseful - performance. In practice, trial result close to the noiseful end of - the spectrum happens only rarely. The worse the performance value - is, the more rarely it is seen in a trial. Therefore, the extreme - noiseful end of the SUT spectrum is not observable among trial - results. Also, the extreme noiseless end of the SUT spectrum is - unlikely to be observable, this time because some small noise effects - are likely to occur multiple times during a trial. - - Unless specified otherwise, this document's focus is on the - potentially observable ends of the SUT performance spectrum, as - opposed to the extreme ones. - - When focusing on the DUT, the benchmarking effort should ideally aim - to eliminate only the SUT noise from SUT measurements. However, this - is currently not feasible in practice, as there are no realistic - enough models available to distinguish SUT noise from DUT - fluctuations, based on authors' experience and available literature. - - Assuming a well-constructed SUT, the DUT is likely its primary - performance bottleneck. In this case, we can define the DUT's ideal - noiseless performance as the noiseless end of the SUT performance - spectrum, especially for throughput. However, other performance - metrics, such as latency, may require additional considerations. - - Note that by this definition, DUT noiseless performance also - minimizes the impact of DUT fluctuations, as much as realistically - possible for a given trial duration. - - MLRsearch methodology aims to solve the DUT in SUT problem by - estimating the noiseless end of the SUT performance spectrum using a - limited number of trial results. - - Any improvements to the throughput search algorithm, aimed at better - dealing with software networking SUT and DUT setup, should employ - strategies recognizing the presence of SUT noise, allowing the - discovery of (proxies for) DUT noiseless performance at different - levels of sensitivity to SUT noise. - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 7] - -Internet-Draft MLRsearch July 2024 - - -2.3. Repeatability and Comparability - - [RFC2544] does not suggest to repeat throughput search. And from - just one discovered throughput value, it cannot be determined how - repeatable that value is. Poor repeatability then leads to poor - comparability, as different benchmarking teams may obtain varying - throughput values for the same SUT, exceeding the expected - differences from search precision. - - [RFC2544] throughput requirements (60 seconds trial and no tolerance - of a single frame loss) affect the throughput results in the - following way. The SUT behavior close to the noiseful end of its - performance spectrum consists of rare occasions of significantly low - performance, but the long trial duration makes those occasions not so - rare on the trial level. Therefore, the binary search results tend - to wander away from the noiseless end of SUT performance spectrum, - more frequently and more widely than short trials would, thus causing - poor throughput repeatability. - - The repeatability problem can be addressed by defining a search - procedure that identifies a consistent level of performance, even if - it does not meet the strict definition of throughput in [RFC2544]. - - According to the SUT performance spectrum model, better repeatability - will be at the noiseless end of the spectrum. Therefore, solutions - to the DUT in SUT problem will help also with the repeatability - problem. - - Conversely, any alteration to [RFC2544] throughput search that - improves repeatability should be considered as less dependent on the - SUT noise. - - An alternative option is to simply run a search multiple times, and - report some statistics (e.g. average and standard deviation). This - can be used for a subset of tests deemed more important, but it makes - the search duration problem even more pronounced. - -2.4. Throughput with Non-Zero Loss - - [RFC1242] (section 3.17 Throughput) defines throughput as: The - maximum rate at which none of the offered frames are dropped by the - device. - - Then, it says: Since even the loss of one frame in a data stream can - cause significant delays while waiting for the higher level protocols - to time out, it is useful to know the actual maximum data rate that - the device can support. - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 8] - -Internet-Draft MLRsearch July 2024 - - - However, many benchmarking teams accept a small, non-zero loss ratio - as the goal for their load search. - - Motivations are many: - - * Modern protocols tolerate frame loss better, compared to the time - when [RFC1242] and [RFC2544] were specified. - - * Trials nowadays send way more frames within the same duration, - increasing the chance of a small SUT performance fluctuation being - enough to cause frame loss. - - * Small bursts of frame loss caused by noise have otherwise smaller - impact on the average frame loss ratio observed in the trial, as - during other parts of the same trial the SUT may work more closely - to its noiseless performance, thus perhaps lowering the Trial Loss - Ratio below the Goal Loss Ratio value. - - * If an approximation of the SUT noise impact on the Trial Loss - Ratio is known, it can be set as the Goal Loss Ratio. - - Regardless of the validity of all similar motivations, support for - non-zero loss goals makes any search algorithm more user-friendly. - [RFC2544] throughput is not user-friendly in this regard. - - Furthermore, allowing users to specify multiple loss ratio values, - and enabling a single search to find all relevant bounds, - significantly enhances the usefulness of the search algorithm. - - Searching for multiple Search Goals also helps to describe the SUT - performance spectrum better than the result of a single Search Goal. - For example, the repeated wide gap between zero and non-zero loss - loads indicates the noise has a large impact on the observed - performance, which is not evident from a single goal load search - procedure result. - - It is easy to modify the vanilla bisection to find a lower bound for - the intended load that satisfies a non-zero Goal Loss Ratio. But it - is not that obvious how to search for multiple goals at once, hence - the support for multiple Search Goals remains a problem. - -2.5. Inconsistent Trial Results - - While performing throughput search by executing a sequence of - measurement trials, there is a risk of encountering inconsistencies - between trial results. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 9] - -Internet-Draft MLRsearch July 2024 - - - The plain bisection never encounters inconsistent trials. But - [RFC2544] hints about the possibility of inconsistent trial results, - in two places in its text. The first place is section 24, where full - trial durations are required, presumably because they can be - inconsistent with the results from short trial durations. The second - place is section 26.3, where two successive zero-loss trials are - recommended, presumably because after one zero-loss trial there can - be a subsequent inconsistent non-zero-loss trial. - - Examples include: - - * A trial at the same load (same or different trial duration) - results in a different Trial Loss Ratio. - - * A trial at a higher load (same or different trial duration) - results in a smaller Trial Loss Ratio. - - Any robust throughput search algorithm needs to decide how to - continue the search in the presence of such inconsistencies. - Definitions of throughput in [RFC1242] and [RFC2544] are not specific - enough to imply a unique way of handling such inconsistencies. - - Ideally, there will be a definition of a new quantity which both - generalizes throughput for non-zero-loss (and other possible - repeatability enhancements), while being precise enough to force a - specific way to resolve trial result inconsistencies. But until such - a definition is agreed upon, the correct way to handle inconsistent - trial results remains an open problem. - -3. MLRsearch Specification - - This section describes MLRsearch specification including all - technical definitions needed for evaluating whether a particular test - procedure complies with MLRsearch specification. - -3.1. Overview - - MLRsearch specification describes a set of abstract system - components, acting as functions with specified inputs and outputs. - - A test procedure is said to comply with MLRsearch specification if it - can be conceptually divided into analogous components, each - satisfying requirements for the corresponding MLRsearch component. - - - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 10] - -Internet-Draft MLRsearch July 2024 - - - The Measurer component is tasked to perform trials, the Controller - component is tasked to select trial loads and durations, the Manager - component is tasked to pre-configure everything and to produce the - test report. The test report explicitly states Search Goals (as the - Controller Inputs) and corresponding Goal Results (Controller - Outputs). - - The Manager calls the Controller once, the Controller keeps calling - the Measurer until all stopping conditions are met. - - The part where Controller calls the Measurer is called the search. - Any activity done by the Manager before it calls the Controller (or - after Controller returns) is not considered to be part of the search. - - MLRsearch specification prescribes regular search results and - recommends their stopping conditions. Irregular search results are - also allowed, they may have different requirements and stopping - conditions. - - Search results are based on load classification. When measured - enough, any chosen load either achieves of fails each search goal, - thus becoming a lower or an upper bound for that goal. When the - relevant bounds are at loads that are close enough (according to goal - precision), the regular result is found. Search stops when all - regular results are found (or if some goals are proven to have only - irregular results). - -3.2. Measurement Quantities - - MLRsearch specification uses a number of measurement quantities. - - In general, MLRsearch specification does not require particular units - to be used, but it is REQUIRED for the test report to state all the - units. For example, ratio quantities can be dimensionless numbers - between zero and one, but may be expressed as percentages instead. - - For convenience, a group of quantities can be treated as a composite - quantity, One constituent of a composite quantity is called an - attribute, and a group of attribute values is called an instance of - that composite quantity. - - Some attributes are not independent from others, and they can be - calculated from other attributes. Such quantites are called derived - quantities. - - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 11] - -Internet-Draft MLRsearch July 2024 - - -3.3. Existing Terms - - RFC 1242 "Benchmarking Terminology for Network Interconnect Devices" - contains basic definitions, and RFC 2544 "Benchmarking Methodology - for Network Interconnect Devices" contains discussions of a number of - terms and additional methodology requirements. RFC 2285 adds more - terms and discussions, describing some known situations in more - precise way. - - All three documents should be consulted before attempting to make use - of this document. - - Definitions of some central terms are copied and discussed in - subsections. - -3.3.1. SUT - - Defined in [RFC2285] (section 3.1.2 System Under Test (SUT)) as - follows. - - Definition: - - The collective set of network devices to which stimulus is offered as - a single entity and response measured. - - Discussion: - - An SUT consisting of a single network device is also allowed. - -3.3.2. DUT - - Defined in [RFC2285] (section 3.1.1 Device Under Test (DUT)) as - follows. - - Definition: - - The network forwarding device to which stimulus is offered and - response measured. - - Discussion: - - DUT, as a sub-component of SUT, is only indirectly mentioned in - MLRsearch specification, but is of key relevance for its motivation. - -3.3.3. Trial - - A trial is the part of the test described in [RFC2544] (section 23. - Trial description). - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 12] - -Internet-Draft MLRsearch July 2024 - - - Definition: - - A particular test consists of multiple trials. Each trial returns - one piece of information, for example the loss rate at a particular - input frame rate. Each trial consists of a number of phases: - - a) If the DUT is a router, send the routing update to the "input" - port and pause two seconds to be sure that the routing has settled. - - b) Send the "learning frames" to the "output" port and wait 2 seconds - to be sure that the learning has settled. Bridge learning frames are - frames with source addresses that are the same as the destination - addresses used by the test frames. Learning frames for other - protocols are used to prime the address resolution tables in the DUT. - The formats of the learning frame that should be used are shown in - the Test Frame Formats document. - - c) Run the test trial. - - d) Wait for two seconds for any residual frames to be received. - - e) Wait for at least five seconds for the DUT to restabilize. - - Discussion: - - The definition describes some traits, it is not clear whether all of - them are REQUIRED, or some of them are only RECOMMENDED. - - For the purposes of the MLRsearch specification, it is ALLOWED for - the test procedure to deviate from the [RFC2544] description, but any - such deviation MUST be made explicit in the test report. - - Trials are the only stimuli the SUT is expected to experience during - the search. - - In some discussion paragraphs, it is useful to consider the traffic - as sent and received by a tester, as implicitly defined in [RFC2544] - (section 6. Test set up). - - An example of deviation from [RFC2544] is using shorter wait times. - -3.4. Trial Terms - - This section defines new and redefine existing terms for quantities - relevant as inputs or outputs of trial, as used by the Measurer - component. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 13] - -Internet-Draft MLRsearch July 2024 - - -3.4.1. Trial Duration - - Definition: - - Trial duration is the intended duration of the traffic for a trial. - - Discussion: - - In general, this quantity does not include any preparation nor - waiting described in section 23 of [RFC2544] (section 23. Trial - description). - - While any positive real value may be provided, some Measurer - implementations MAY limit possible values, e.g. by rounding down to - neared integer in seconds. In that case, it is RECOMMENDED to give - such inputs to the Controller so the Controller only proposes the - accepted values. Alternatively, the test report MUST present the - rounded values as Search Goal attributes. - -3.4.2. Trial Load - - Definition: - - The trial load is the intended load for a trial - - Discussion: - - For test report purposes, it is assumed that this is a constant load - by default. This MAY be only an average load, e.g. when the traffic - is intended to be busty, e.g. as suggested in [RFC2544] (section 21. - Bursty traffic), but the test report MUST explicitly mention how non- - constant the traffic is. - - Trial load is the quantity defined as Constant Load of [RFC1242] - (section 3.4 Constant Load), Data Rate of [RFC2544] (section 14. - Bidirectional traffic) and Intended Load of [RFC2285] (section 3.5.1 - Intended load (Iload)). All three definitions specify that this - value applies to one (input or output) interface. - - For test report purposes, multi-interface aggregate load MAY be - reported, this is understood as the same quantity expressed using - different units. From the report it MUST be clear whether a - particular trial load value is per one interface, or an aggregate - over all interfaces. - - Similarly to trial duration, some Measurers may limit the possible - values of trial load. Contrary to trial duration, the test report is - NOT REQUIRED to document such behavior. - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 14] - -Internet-Draft MLRsearch July 2024 - - - It is ALLOWED to combine trial load and trial duration in a way that - would not be possible to achieve using any integer number of data - frames. - -3.4.3. Trial Input - - Definition: - - Trial Input is a composite quantity, consisting of two attributes: - trial duration and trial load. - - Discussion: - - When talking about multiple trials, it is common to say "Trial - Inputs" to denote all corresponding Trial Input instances. - - A Trial Input instance acts as the input for one call of the Measurer - component. - - Contrary to other composite quantities, MLRsearch implementations are - NOT ALLOWED to add optional attributes here. This improves - interoperability between various implementations of the Controller - and the Measurer. - -3.4.4. Traffic Profile - - Definition: - - Traffic profile is a composite quantity containing attributes other - than trial load and trial duration, needed for unique determination - of the trial to be performed. - - Discussion: - - All its attributes are assumed to be constant during the search, and - the composite is configured on the Measurer by the Manager before the - search starts. This is why the traffic profile is not part of the - Trial Input. - - As a consequence, implementations of the Manager and the Measurer - must be aware of their common set of capabilities, so that the - traffic profile uniquely defines the traffic during the search. The - important fact is that none of those capabilities have to be known by - the Controller implementations. - - The traffic profile SHOULD contain some specific quantities, for - example [RFC2544] (section 9. Frame sizes) governs data link frame - size as defined in [RFC1242] (section 3.5 Data link frame size). - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 15] - -Internet-Draft MLRsearch July 2024 - - - Several more specific quantities may be RECOMMENDED, depending on - media type. For example, [RFC2544] (Appendix C) lists frame formats - and protocol addresses, as recommended from [RFC2544] (section 8. - Frame formats) and [RFC2544] (section 12. Protocol addresses). - - Depending on SUT configuration, e.g. when testing specific protocols, - additional attributes MUST be included in the traffic profile and in - the test report. - - Example: [RFC8219] (section 5.3. Traffic Setup) introduces traffic - setups consisting of a mix of IPv4 and IPv6 traffic - the implied - traffic profile therefore must include an attribute for their - percentage. - - Other traffic properties that need to be somehow specified in Traffic - Profile include: [RFC2544] (section 14. Bidirectional traffic), - [RFC2285] (section 3.3.3 Fully meshed traffic), and [RFC2544] - (section 11. Modifiers). - -3.4.5. Trial Forwarding Ratio - - Definition: - - The trial forwarding ratio is a dimensionless floating point value. - It MUST range between 0.0 and 1.0, both inclusive. It is calculated - by dividing the number of frames successfully forwarded by the SUT by - the total number of frames expected to be forwarded during the trial - - Discussion: - - For most traffic profiles, "expected to be forwarded" means "intended - to get transmitted from Tester towards SUT". - - Trial forwarding ratio MAY be expressed in other units (e.g. as a - percentage) in the test report. - - Note that, contrary to loads, frame counts used to compute trial - forwarding ratio are aggregates over all SUT output interfaces. - - Questions around what is the correct number of frames that should - have been forwarded is generally outside of the scope of this - document. - -3.4.6. Trial Loss Ratio - - Definition: - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 16] - -Internet-Draft MLRsearch July 2024 - - - The Trial Loss Ratio is equal to one minus the trial forwarding - ratio. - - Discussion: - - 100% minus the trial forwarding ratio, when expressed as a - percentage. - - This is almost identical to Frame Loss Rate of [RFC1242] (section 3.6 - Frame Loss Rate), the only minor difference is that Trial Loss Ratio - does not need to be expressed as a percentage. - -3.4.7. Trial Forwarding Rate - - Definition: - - The trial forwarding rate is a derived quantity, calculated by - multiplying the trial load by the trial forwarding ratio. - - Discussion: - - It is important to note that while similar, this quantity is not - identical to the Forwarding Rate as defined in [RFC2285] (section - 3.6.1 Forwarding rate (FR)). The latter is specific to one output - interface only, whereas the trial forwarding ratio is based on frame - counts aggregated over all SUT output interfaces. - -3.4.8. Trial Effective Duration - - Definition: - - Trial effective duration is a time quantity related to the trial, by - default equal to the trial duration. - - Discussion: - - This is an optional feature. If the Measurer does not return any - trial effective duration value, the Controller MUST use the trial - duration value instead. - - Trial effective duration may be any time quantity chosen by the - Measurer to be used for time-based decisions in the Controller. - - The test report MUST explain how the Measurer computes the returned - trial effective duration values, if they are not always equal to the - trial duration. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 17] - -Internet-Draft MLRsearch July 2024 - - - This feature can be beneficial for users who wish to manage the - overall search duration, rather than solely the traffic portion of - it. Simply measure the duration of the whole trial (waits including) - and use that as the trial effective duration. - - Also, this is a way for the Measurer to inform the Controller about - its surprising behavior, for example when rounding the trial duration - value. - -3.4.9. Trial Output - - Definition: - - Trial Output is a composite quantity. The REQUIRED attributes are - Trial Loss Ratio, trial effective duration and trial forwarding rate. - - Discussion: - - When talking about multiple trials, it is common to say "Trial - Outputs" to denote all corresponding Trial Output instances. - - Implementations may provide additional (optional) attributes. The - Controller implementations MUST ignore values of any optional - attribute they are not familiar with, except when passing Trial - Output instance to the Manager. - - Example of an optional attribute: The aggregate number of frames - expected to be forwarded during the trial, especially if it is not - just (a rounded-up value) implied by trial load and trial duration. - - While [RFC2285] (Section 3.5.2 Offered load (Oload)) requires the - offered load value to be reported for forwarding rate measurements, - it is NOT REQUIRED in MLRsearch specification. - -3.4.10. Trial Result - - Definition: - - Trial result is a composite quantity, consisting of the Trial Input - and the Trial Output. - - Discussion: - - When talking about multiple trials, it is common to say "trial - results" to denote all corresponding trial result instances. - - While implementations SHOULD NOT include additional attributes with - independent values, they MAY include derived quantities. - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 18] - -Internet-Draft MLRsearch July 2024 - - -3.5. Goal Terms - - This section defines new and redefine existing terms for quantities - indirectly relevant for inputs or outputs of the Controller - component. - - Several goal attributes are defined before introducing the main - component quantity: the Search Goal. - -3.5.1. Goal Final Trial Duration - - Definition: - - A threshold value for trial durations. - - Discussion: - - This attribute value MUST be positive. - - A trial with Trial Duration at least as long as the Goal Final Trial - Duration is called a full-length trial (with respect to the given - Search Goal). - - A trial that is not full-length is called a short trial. - - Informally, while MLRsearch is allowed to perform short trials, the - results from such short trials have only limited impact on search - results. - - One trial may be full-length for some Search Goals, but not for - others. - - The full relation of this goal to Controller Output is defined later - in this document in subsections of [Goal Result] (#Goal-Result). For - example, the Conditional Throughput for this goal is computed only - from full-length trial results. - -3.5.2. Goal Duration Sum - - Definition: - - A threshold value for a particular sum of trial effective durations. - - Discussion: - - This attribute value MUST be positive. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 19] - -Internet-Draft MLRsearch July 2024 - - - Informally, even when looking only at full-length trials, MLRsearch - may spend up to this time measuring the same load value. - - If the Goal Duration Sum is larger than the Goal Final Trial - Duration, multiple full-length trials may need to be performed at the - same load. - - See [TST009 Example] (#TST009-Example) for an example where - possibility of multiple full-length trials at the same load is - intended. - - A Goal Duration Sum value lower than the Goal Final Trial Duration - (of the same goal) could save some search time, but is NOT - RECOMMENDED. See [Relevant Upper Bound] (#Relevant-Upper-Bound) for - partial explanation. - -3.5.3. Goal Loss Ratio - - Definition: - - A threshold value for Trial Loss Ratios. - - Discussion: - - Attribute value MUST be non-negative and smaller than one. - - A trial with Trial Loss Ratio larger than a Goal Loss Ratio value is - called a lossy trial, with respect to given Search Goal. - - Informally, if a load causes too many lossy trials, the Relevant - Lower Bound for this goal will be smaller than that load. - - If a trial is not lossy, it is called a low-loss trial, or - (specifically for zero Goal Loss Ratio value) zero-loss trial. - -3.5.4. Goal Exceed Ratio - - Definition: - - A threshold value for a particular ratio of sums of Trial Effective - Durations. - - Discussion: - - Attribute value MUST be non-negative and smaller than one. - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 20] - -Internet-Draft MLRsearch July 2024 - - - See later sections for details on which sums. Specifically, the - direct usage is only in [Appendix A: Load Classification] (#Appendix- - A:-Load-Classification) and [Appendix B: Conditional Throughput] - (#Appendix-B:-Conditional-Throughput). The impact of that usage is - discussed in subsections leading to [Goal Result] (#Goal-Result). - - Informally, the impact of lossy trials is controlled by this value. - Effectively, Goal Exceed Ratio is a percentage of full-length trials - that may be lossy without the load being classified as the [Relevant - Upper Bound] (#Relevant-Upper-Bound). - -3.5.5. Goal Width - - Definition: - - A value used as a threshold for deciding whether two trial load - values are close enough. - - Discussion: - - If present, the value MUST be positive. - - Informally, this acts as a stopping condition, controlling the - precision of the search. The search stops if every goal has reached - its precision. - - Implementations without this attribute MUST give the Controller other - ways to control the search stopping conditions. - - Absolute load difference and relative load difference are two popular - choices, but implementations may choose a different way to specify - width. - - The test report MUST make it clear what specific quantity is used as - Goal Width. - - It is RECOMMENDED to set the Goal Width (as relative difference) - value to a value no smaller than the Goal Loss Ratio. (The reason is - not obvious, see [Throughput] (#Throughput) if interested.) - -3.5.6. Search Goal - - Definition: - - The Search Goal is a composite quantity consisting of several - attributes, some of them are required. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 21] - -Internet-Draft MLRsearch July 2024 - - - Required attributes: - Goal Final Trial Duration - Goal Duration Sum - - Goal Loss Ratio - Goal Exceed Ratio - - Optional attribute: - Goal Width - - Discussion: - - Implementations MAY add their own attributes. Those additional - attributes may be required by the implementation even if they are not - required by MLRsearch specification. But it is RECOMMENDED for those - implementations to support missing values by computing reasonable - defaults. - - The meaning of listed attributes is formally given only by their - indirect effect on the search results. - - Informally, later sections provide additional intuitions and examples - of the Search Goal attribute values. - - An example of additional attributes required by some implementations - is Goal Initial Trial Duration, together with another attribute that - controls possible intermediate Trial Duration values. The reasonable - default in this case is using the Goal Final Trial Duration and no - intermediate values. - -3.5.7. Controller Input - - Definition: - - Controller Input is a composite quantity required as an input for the - Controller. The only REQUIRED attribute is a list of Search Goal - instances. - - Discussion: - - MLRsearch implementations MAY use additional attributes. Those - additional attributes may be required by the implementation even if - they are not required by MLRsearch specification. - - Formally, the Manager does not apply any Controller configuration - apart from one Controller Input instance. - - For example, Traffic Profile is configured on the Measurer by the - Manager (without explicit assistance of the Controller). - - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 22] - -Internet-Draft MLRsearch July 2024 - - - The order of Search Goal instances in a list SHOULD NOT have a big - impact on Controller Output (see section [Controller Output] - (#Controller-Output) , but MLRsearch implementations MAY base their - behavior on the order of Search Goal instances in a list. - - An example of an optional attribute (outside the list of Search - Goals) required by some implementations is Max Load. While this is a - frequently used configuration parameter, already governed by - [RFC2544] (section 20. Maximum frame rate) and [RFC2285] (3.5.3 - Maximum offered load (MOL)), some implementations may detect or - discover it instead. - - In MLRsearch specification, the [Relevant Upper Bound] (#Relevant- - Upper-Bound) is added as a required attribute precisely because it - makes the search result independent of Max Load value. - -3.6. Search Goal Examples - -3.6.1. RFC2544 Goal - - The following set of values makes the search result unconditionally - compliant with [RFC2544] (section 24 Trial duration) - - * Goal Final Trial Duration = 60 seconds - - * Goal Duration Sum = 60 seconds - - * Goal Loss Ratio = 0% - - * Goal Exceed Ratio = 0% - - The latter two attributes are enough to make the search goal - conditionally compliant, adding the first attribute makes it - unconditionally compliant. - - The second attribute (Goal Duration Sum) only prevents MLRsearch from - repeating zero-loss full-length trials. - - Non-zero exceed ratio could prolong the search and allow loss - inversion between lower-load lossy short trial and higher-load full- - length zero-loss trial. From [RFC2544] alone, it is not clear - whether that higher load could be considered as compliant throughput. - - - - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 23] - -Internet-Draft MLRsearch July 2024 - - -3.6.2. TST009 Goal - - One of the alternatives to RFC2544 is described in [TST009] (section - 12.3.3 Binary search with loss verification). The idea there is to - repeat lossy trials, hoping for zero loss on second try, so the - results are closer to the noiseless end of performance sprectum, and - more repeatable and comparable. - - Only the variant with "z = infinity" is achievable with MLRsearch. - - For example, for "r = 2" variant, the following search goal should be - used: - - * Goal Final Trial Duration = 60 seconds - - * Goal Duration Sum = 120 seconds - - * Goal Loss Ratio = 0% - - * Goal Exceed Ratio = 50% - - If the first 60s trial has zero loss, it is enough for MLRsearch to - stop measuring at that load, as even a second lossy trial would still - fit within the exceed ratio. - - But if the first trial is lossy, MLRsearch needs to perform also the - second trial to classify that load. As Goal Duration Sum is twice as - long as Goal Final Trial Duration, third full-length trial is never - needed. - -3.7. Result Terms - - Before defining the output of the Controller, it is useful to define - what the Goal Result is. - - The Goal Result is a composite quantity. - - Following subsections define its attribute first, before describing - the Goal Result quantity. - - There is a correspondence between Search Goals and Goal Results. - Most of the following subsections refer to a given Search Goal, when - defining attributes of the Goal Result. Conversely, at the end of - the search, each Search Goal has its corresponding Goal Result. - - Conceptually, the search can be seen as a process of load - classification, where the Controller attempts to classify some loads - as an Upper Bound or a Lower Bound with respect to some Search Goal. - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 24] - -Internet-Draft MLRsearch July 2024 - - - Before defining real attributes of the goal result, it is useful to - define bounds in general. - -3.7.1. Relevant Upper Bound - - Definition: - - The Relevant Upper Bound is the smallest trial load value that is - classified at the end of the search as an upper bound (see - [Appendix A: Load Classification] (#Appendix-A:-Load-Classification)) - for the given Search Goal. - - Discussion: - - One search goal can have many different load classified as an upper - bound. At the end of the search, one of those loads will be the - smallest, becoming the relevant upper bound for that goal. - - In more detail, the set of all trial outputs (both short and full- - length, enough of them according to Goal Duration Sum) performed at - that smallest load failed to uphold all the requirements of the given - Search Goal, mainly the Goal Loss Ratio in combination with the Goal - Exceed Ratio. - - If Max Load does not cause enough lossy trials, the Relevant Upper - Bound does not exist. Conversely, if Relevant Upper Bound exists, it - is not affected by Max Load value. - -3.7.2. Relevant Lower Bound - - Definition: - - The Relevant Lower Bound is the largest trial load value among those - smaller than the Relevant Upper Bound, that got classified at the end - of the search as a lower bound (see [Appendix A: Load Classification] - (#Appendix-A:-Load-Classification)) for the given Search Goal. - - Discussion: - - Only among loads smaller that the relevant upper bound, the largest - load becomes the relevant lower bound. With loss inversion, stricter - upper bound matters. - - In more detail, the set of all trial outputs (both short and full- - length, enough of them according to Goal Duration Sum) performed at - that largest load managed to uphold all the requirements of the given - Search Goal, mainly the Goal Loss Ratio in combination with the Goal - Exceed Ratio. - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 25] - -Internet-Draft MLRsearch July 2024 - - - Is no load had enough low-loss trials, the relevant lower bound MAY - not exist. - - Strictly speaking, if the Relevant Upper Bound does not exist, the - Relevant Lower Bound also does not exist. In that case, Max Load is - classified as a lower bound, but it is not clear whether a higher - lower bound would be found if the search used a higher Max Load - value. - - For a regular Goal Result, the distance between the Relevant Lower - Bound and the Relevant Upper Bound MUST NOT be larger than the Goal - Width, if the implementation offers width as a goal attribute. - - Searching for anther search goal may cause a loss inversion - phenomenon, where a lower load is classified as an upper bound, but - also a higher load is classified as a lower bound for the same search - goal. The definition of the Relevant Lower Bound ignores such high - lower bounds. - -3.7.3. Conditional Throughput - - Definition: - - The Conditional Throughput (see section [Appendix B: Conditional - Throughput] (#Appendix-B:-Conditional-Throughput)) as evaluated at - the Relevant Lower Bound of the given Search Goal at the end of the - search. - - Discussion: - - Informally, this is a typical trial forwarding rate, expected to be - seen at the Relevant Lower Bound of the given Search Goal. - - But frequently it is only a conservative estimate thereof, as - MLRsearch implementations tend to stop gathering more data as soon as - they confirm the value cannot get worse than this estimate within the - Goal Duration Sum. - - This value is RECOMMENDED to be used when evaluating repeatability - and comparability if different MLRsearch implementations. - -3.7.4. Goal Result - - Definition: - - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 26] - -Internet-Draft MLRsearch July 2024 - - - The Goal Result is a composite quantity consisting of several - attributes. Relevant Upper Bound and Relevant Lower Bound are - REQUIRED attributes, Conditional Throughput is a RECOMMENDED - attribute. - - Discussion: - - Depending on SUT behavior, it is possible that one or both relevant - bounds do not exist. The goal result instance where the required - attribute values exist is informally called a Regular Goal Result - instance, so we can say some goals reached Irregular Goal Results. - - A typical Irregular Goal Result is when all trials at the Max Load - have zero loss, as the Relevant Upper Bound does not exist in that - case. - - It is RECOMMENDED that the test report will display such results - appropriately, although MLRsearch specification does not prescibe - how. - - Anything else regarging Irregular Goal Results, including their role - in stopping conditions of the search is outside the scope of this - document. - -3.7.5. Search Result - - Definition: - - The Search Result is a single composite object that maps each Search - Goal instance to a corresponding Goal Result instance. - - Discussion: - - Alternatively, the Search Result can be implemented as an ordered - list of the Goal Result instances, matching the order of Search Goal - instances. - - The Search Result (as a mapping) MUST map from all the Search Goal - instances present in the Controller Input. - -3.7.6. Controller Output - - Definition: - - The Controller Output is a composite quantity returned from the - Controller to the Manager at the end of the search. The Search - Result instance is its only REQUIRED attribute. - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 27] - -Internet-Draft MLRsearch July 2024 - - - Discussion: - - MLRsearch implementation MAY return additional data in the Controller - Output. - -3.8. MLRsearch Architecture - - MLRsearch architecture consists of three main system components: the - Manager, the Controller, and the Measurer. - - The architecture also implies the presence of other components, such - as the SUT and the Tester (as a sub-component of the Measurer). - - Protocols of communication between components are generally left - unspecified. For example, when MLRsearch specification mentions - "Controller calls Measurer", it is possible that the Controller - notifies the Manager to call the Measurer indirectly instead. This - way the Measurer implementations can be fully independent from the - Controller implementations, e.g. programmed in different programming - languages. - -3.8.1. Measurer - - Definition: - - The Measurer is an abstract system component that when called with a - [Trial Input] (#Trial-Input) instance, performs one [Trial] (#Trial), - and returns a [Trial Output] (#Trial-Output) instance. - - Discussion: - - This definition assumes the Measurer is already initialized. In - practice, there may be additional steps before the search, e.g. when - the Manager configures the traffic profile (either on the Measurer or - on its tester sub-component directly) and performs a warmup (if the - tester requires one). - - It is the responsibility of the Measurer implementation to uphold any - requirements and assumptions present in MLRsearch specification, e.g. - trial forwarding ratio not being larger than one. - - Implementers have some freedom. For example [RFC2544] (section 10. - Verifying received frames) gives some suggestions (but not - requirements) related to duplicated or reordered frames. - Implementations are RECOMMENDED to document their behavior related to - such freedoms in as detailed a way as possible. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 28] - -Internet-Draft MLRsearch July 2024 - - - It is RECOMMENDED to benchmark the test equipment first, e.g. connect - sender and receiver directly (without any SUT in the path), find a - load value that guarantees the offered load is not too far from the - intended load, and use that value as the Max Load value. When - testing the real SUT, it is RECOMMENDED to turn any big difference - between the intended load and the offered load into increased Trial - Loss Ratio. - - Neither of the two recommendations are made into requirements, - because it is not easy to tell when the difference is big enough, in - a way thay would be dis-entangled from other Measurer freedoms. - -3.8.2. Controller - - Definition: - - The Controller is an abstract system component that when called with - a Controller Input instance repeatedly computes Trial Input instance - for the Measurer, obtains corresponding Trial Output instances, and - eventually returns a Controller Output instance. - - Discussion: - - Informally, the Controller has big freedom in selection of Trial - Inputs, and the implementations want to achieve the Search Goals in - the shortest expected time. - - The Controller's role in optimizing the overall search time - distinguishes MLRsearch algorithms from simpler search procedures. - - Informally, each implementation can have different stopping - conditions. Goal Width is only one example. In practice, - implementation details do not matter, as long as Goal Results are - regular. - -3.8.3. Manager - - Definition: - - The Manager is an abstract system component that is reponsible for - configuring other components, calling the Controller component once, - and for creating the test report following the reporting format as - defined in [RFC2544] (section 26. Benchmarking tests). - - Discussion: - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 29] - -Internet-Draft MLRsearch July 2024 - - - The Manager initializes the SUT, the Measurer (and the Tester if - independent) with their intended configurations before calling the - Controller. - - The Manager does not need to be able to tweak any Search Goal - attributes, but it MUST report all applied attribute values even if - not tweaked. - - In principle, there should be a "user" (human or CI) that "starts" or - "calls" the Manager and receives the report. The Manager MAY be able - to be called more than once whis way. - -3.9. Implementation Compliance - - Any networking measurement setup where there can be logically - delineated system components and there are components satisfying - requirements for the Measurer, the Controller and the Manager, is - considered to be compliant with MLRsearch design. - - These components can be seen as abstractions present in any testing - procedure. For example, there can be a single component acting both - as the Manager and the Controller, but as long as values of required - attributes of Search Goals and Goal Results are visible in the test - report, the Controller Input instance and output instance are - implied. - - For example, any setup for conditionally (or unconditionally) - compliant [RFC2544] throughput testing can be understood as a - MLRsearch architecture, assuming there is enough data to reconstruct - the Relevant Upper Bound. - - See [RFC2544 Goal] (#RFC2544-Goal) subsection for equivalent Search - Goal. - - Any test procedure that can be understood as (one call to the Manager - of) MLRsearch architecture is said to be compliant with MLRsearch - specification. - -4. Additional Considerations - - This section focuses on additional considerations, intuitions and - motivations pertaining to MLRsearch methodology. - - - - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 30] - -Internet-Draft MLRsearch July 2024 - - -4.1. MLRsearch Versions - - The MLRsearch algorithm has been developed in a code-first approach, - a Python library has been created, debugged, used in production and - published in PyPI before the first descriptions (even informal) were - published. - - But the code (and hence the description) was evolving over time. - Multiple versions of the library were used over past several years, - and later code was usually not compatible with earlier descriptions. - - The code in (some version of) MLRsearch library fully determines the - search process (for a given set of configuration parameters), leaving - no space for deviations. - - This historic meaning of MLRsearch, as a family of search algorithm - implementations, leaves plenty of space for future improvements, at - the cost of poor comparability of results of search algoritm - implementations. - - There are two competing needs. There is the need for standardization - in areas critical to comparability. There is also the need to allow - flexibility for implementations to innovate and improve in other - areas. This document defines MLRsearch as a new specification in a - manner that aims to fairly balance both needs. - -4.2. Stopping Conditions - - [RFC2544] prescribes that after performing one trial at a specific - offered load, the next offered load should be larger or smaller, - based on frame loss. - - The usual implementation uses binary search. Here a lossy trial - becomes a new upper bound, a lossless trial becomes a new lower - bound. The span of values between the tightest lower bound and the - tightest upper bound (including both values) forms an interval of - possible results, and after each trial the width of that interval - halves. - - Usually the binary search implementation tracks only the two tightest - bounds, simply calling them bounds. But the old values still remain - valid bounds, just not as tight as the new ones. - - After some number of trials, the tightest lower bound becomes the - throughput. [RFC2544] does not specify when, if ever, should the - search stop. - - MLRsearch introduces a concept of [Goal Width] (#Goal-Width). - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 31] - -Internet-Draft MLRsearch July 2024 - - - The search stops when the distance between the tightest upper bound - and the tightest lower bound is smaller than a user-configured value, - called Goal Width from now on. In other words, the interval width at - the end of the search has to be no larger than the Goal Width. - - This Goal Width value therefore determines the precision of the - result. Due to the fact that MLRsearch specification requires a - particular structure of the result (see [Trial Result] (#Trial- - Result) section), the result itself does contain enough information - to determine its precision, thus it is not required to report the - Goal Width value. - - This allows MLRsearch implementations to use stopping conditions - different from Goal Width. - -4.3. Load Classification - - MLRsearch keeps the basic logic of binary search (tracking tightest - bounds, measuring at the middle), perhaps with minor technical - differences. - - MLRsearch algorithm chooses an intended load (as opposed to the - offered load), the interval between bounds does not need to be split - exactly into two equal halves, and the final reported structure - specifies both bounds. - - The biggest difference is that to classify a load as an upper or - lower bound, MLRsearch may need more than one trial (depending on - configuration options) to be performed at the same intended load. - - In consequence, even if a load already does have few trial results, - it still may be classified as undecided, neither a lower bound nor an - upper bound. - - An explanation of the classification logic is given in the next - section [Logic of Load Classification] (#Logic-of-Load- - Classification), as it heavily relies on other subsections of this - section. - - For repeatability and comparability reasons, it is important that - given a set of trial results, all implementations of MLRsearch - classify the load equivalently. - -4.4. Loss Ratios - - Another difference between MLRsearch and [RFC2544] binary search is - in the goals of the search. [RFC2544] has a single goal, based on - classifying full-length trials as either lossless or lossy. - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 32] - -Internet-Draft MLRsearch July 2024 - - - MLRsearch, as the name suggests, can search for multiple goals, - differing in their loss ratios. The precise definition of the Goal - Loss Ratio will be given later. The [RFC2544] throughput goal then - simply becomes a zero Goal Loss Ratio. Different goals also may have - different Goal Widths. - - A set of trial results for one specific intended load value can - classify the load as an upper bound for some goals, but a lower bound - for some other goals, and undecided for the rest of the goals. - - Therefore, the load classification depends not only on trial results, - but also on the goal. The overall search procedure becomes more - complicated, when compared to binary search with a single goal, but - most of the complications do not affect the final result, except for - one phenomenon, loss inversion. - -4.5. Loss Inversion - - In [RFC2544] throughput search using bisection, any load with a lossy - trial becomes a hard upper bound, meaning every subsequent trial has - a smaller intended load. - - But in MLRsearch, a load that is classified as an upper bound for one - goal may still be a lower bound for another goal, and due to the - other goal MLRsearch will probably perform trials at even higher - loads. What to do when all such higher load trials happen to have - zero loss? Does it mean the earlier upper bound was not real? Does - it mean the later lossless trials are not considered a lower bound? - Surely we do not want to have an upper bound at a load smaller than a - lower bound. - - MLRsearch is conservative in these situations. The upper bound is - considered real, and the lossless trials at higher loads are - considered to be a coincidence, at least when computing the final - result. - - This is formalized using new notions, the [Relevant Upper Bound] - (#Relevant-Upper-Bound) and the [Relevant Lower Bound] (#Relevant- - Lower-Bound). Load classification is still based just on the set of - trial results at a given intended load (trials at other loads are - ignored), making it possible to have a lower load classified as an - upper bound, and a higher load classified as a lower bound (for the - same goal). The Relevant Upper Bound (for a goal) is the smallest - load classified as an upper bound. But the Relevant Lower Bound is - not simply the largest among lower bounds. It is the largest load - among loads that are lower bounds while also being smaller than the - Relevant Upper Bound. - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 33] - -Internet-Draft MLRsearch July 2024 - - - With these definitions, the Relevant Lower Bound is always smaller - than the Relevant Upper Bound (if both exist), and the two relevant - bounds are used analogously as the two tightest bounds in the binary - search. When they are less than the Goal Width apart, the relevant - bounds are used in the output. - - One consequence is that every trial result can have an impact on the - search result. That means if your SUT (or your traffic generator) - needs a warmup, be sure to warm it up before starting the search. - -4.6. Exceed Ratio - - The idea of performing multiple trials at the same load comes from a - model where some trial results (those with high loss) are affected by - infrequent effects, causing poor repeatability of [RFC2544] - throughput results. See the discussion about noiseful and noiseless - ends of the SUT performance spectrum in section [DUT in SUT] (#DUT- - in-SUT). Stable results are closer to the noiseless end of the SUT - performance spectrum, so MLRsearch may need to allow some frequency - of high-loss trials to ignore the rare but big effects near the - noiseful end. - - MLRsearch can do such trial result filtering, but it needs a - configuration option to tell it how frequent can the infrequent big - loss be. This option is called the exceed ratio. It tells MLRsearch - what ratio of trials (more exactly what ratio of trial seconds) can - have a [Trial Loss Ratio] (#Trial-Loss-Ratio) larger than the Goal - Loss Ratio and still be classified as a lower bound. Zero exceed - ratio means all trials have to have a Trial Loss Ratio equal to or - smaller than the Goal Loss Ratio. - - For explainability reasons, the RECOMMENDED value for exceed ratio is - 0.5, as it simplifies some later concepts by relating them to the - concept of median. - -4.7. Duration Sum - - When more than one trial is intended to classify a load, MLRsearch - also needs something that controls the number of trials needed. - Therefore, each goal also has an attribute called duration sum. - - The meaning of a [Goal Duration Sum] (#Goal-Duration-Sum) is that - when a load has (full-length) trials whose trial durations when - summed up give a value at least as big as the Goal Duration Sum - value, the load is guaranteed to be classified either as an upper - bound or a lower bound for that goal. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 34] - -Internet-Draft MLRsearch July 2024 - - - Due to the fact that the duration sum has a big impact on the overall - search duration, and [RFC2544] prescribes wait intervals around trial - traffic, the MLRsearch algorithm is allowed to sum durations that are - different from the actual trial traffic durations. - - In the MLRsearch specification, the different duration values are - called [Trial Effective Duration] (#Trial-Effective-Duration). - -4.8. Short Trials - - MLRsearch requires each goal to specify its final trial duration. - Full-length trial is a shorter name for a trial whose intended trial - duration is equal to (or longer than) the goal final trial duration. - - Section 24 of [RFC2544] already anticipates possible time savings - when short trials (shorter than full-length trials) are used. Full- - length trials are the opposite of short trials, so they may also be - called long trials. - - Any MLRsearch implementation may include its own configuration - options which control when and how MLRsearch chooses to use short - trial durations. - - For explainability reasons, when exceed ratio of 0.5 is used, it is - recommended for the Goal Duration Sum to be an odd multiple of the - full trial durations, so Conditional Throughput becomes identical to - a median of a particular set of trial forwarding rates. - - The presence of short trial results complicates the load - classification logic. - - Full details are given later in section [Logic of Load - Classification] (#Logic-of-Load-Classification). In a nutshell, - results from short trials may cause a load to be classified as an - upper bound. This may cause loss inversion, and thus lower the - Relevant Lower Bound, below what would classification say when - considering full-length trials only. - -4.9. Throughput - - Due to the fact that testing equipment takes the intended load as an - input parameter for a trial measurement, any load search algorithm - needs to deal with intended load values internally. - - - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 35] - -Internet-Draft MLRsearch July 2024 - - - But in the presence of goals with a non-zero loss ratio, the intended - load usually does not match the user's intuition of what a throughput - is. The forwarding rate (as defined in [RFC2285] section 3.6.1) is - better, but it is not obvious how to generalize it for loads with - multiple trial results and a non-zero [Goal Loss Ratio] (#Goal-Loss- - Ratio). - - The best example is also the main motivation: hard limit performance. - Even if the medium allows higher performance, the SUT interfaces may - have their additional own limitations, e.g. a specific fps limit on - the NIC (a very common occurance). - - Ideally, those should be known and used when computing Max Load. But - if Max Load is higher that what interface can receive or transmit, - there will be a "hard limit" observed in trial results. Imagine the - hard limit is at 100 Mfps, Max Load is higher, and the goal loss - ratio is 0.5%. If DUT has no additional losses, 0.5% loss ratio will - be achieved at 100.5025 Mfps (the relevant lower bound). But it is - not intuitive to report SUT performance as a value that is larger - than known hard limit. We need a generalization of RFC2544 - throughput, different from just the relevant lower bound. - - MLRsearch defines one such generalization, called the Conditional - Throughput. It is the trial forwarding rate from one of the trials - performed at the load in question. Determining which trial exactly - is defined in [MLRsearch Specification] (#MLRsearch-Specification), - and in [Appendix B: Conditional Throughput] (#Appendix-B:- - Conditional-Throughput). - - In the hard limit example, 100.5 Mfps load will still have only 100.0 - Mfps forwarding rate, nicely confirming the known limitation. - - Conditional Throughput is partially related to load classification. - If a load is classified as a lower bound for a goal, the Conditional - Throughput can be calculated from trial results, and guaranteed to - show an loss ratio no larger than the Goal Loss Ratio. - - Note that when comparing the best (all zero loss) and worst case (all - loss just below Goal Loss Ratio), the same Relevant Lower Bound value - may result in the Conditional Throughput differing up to the Goal - Loss Ratio. - - - - - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 36] - -Internet-Draft MLRsearch July 2024 - - - Therefore it is rarely needed to set the Goal Width (if expressed as - the relative difference of loads) below the Goal Loss Ratio. In - other words, setting the Goal Width below the Goal Loss Ratio may - cause the Conditional Throughput for a larger loss ratio to become - smaller than a Conditional Throughput for a goal with a smaller Goal - Loss Ratio, which is counter-intuitive, considering they come from - the same search. Therefore it is RECOMMENDED to set the Goal Width - to a value no smaller than the Goal Loss Ratio. - - Overall, this Conditional Throughput does behave well for - comparability purposes. - -4.10. Search Time - - MLRsearch was primarily developed to reduce the time required to - determine a throughput, either the [RFC2544] compliant one, or some - generalization thereof. The art of achieving short search times is - mainly in the smart selection of intended loads (and intended - durations) for the next trial to perform. - - While there is an indirect impact of the load selection on the - reported values, in practice such impact tends to be small, even for - SUTs with quite a broad performance spectrum. - - A typical example of two approaches to load selection leading to - different Relevant Lower Bounds is when the interval is split in a - very uneven way. Any implementation choosing loads very close to the - current Relevant Lower Bound is quite likely to eventually stumble - upon a trial result with poor performance (due to SUT noise). For an - implementation choosing loads very close to the current Relevant - Upper Bound, this is unlikely, as it examines more loads that can see - a performance close to the noiseless end of the SUT performance - spectrum. - - However, as even splits optimize search duration at give precision, - MLRsearch implementations that prioritize minimizing search time are - unlikely to suffer from any such bias. - - Therefore, this document remains quite vague on load selection and - other optimization details, and configuration attributes related to - them. Assuming users prefer libraries that achieve short overall - search time, the definition of the Relevant Lower Bound should be - strict enough to ensure result repeatability and comparability - between different implementations, while not restricting future - implementations much. - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 37] - -Internet-Draft MLRsearch July 2024 - - -4.11. [RFC2544] Compliance - - Some Search Goal instances lead to results compliant with RFC2544. - See [RFC2544 Goal] (#RFC2544-Goal) for more details regarding both - conditional and unconditional compliance. - - The presence of other Search Goals does not affect the compliance of - this Goal Result. The Relevant Lower Bound and the Conditional - Throughput are in this case equal to each other, and the value is the - [RFC2544] throughput. - -5. Logic of Load Classification - -5.1. Introductory Remarks - - This chapter continues with explanations, but this time more precise - definitions are needed for readers to follow the explanations. - - Descriptions in this section are wordy and implementers should read - [MLRsearch Specification] (#MLRsearch-Specification) section and - Appendices for more concise definitions. - - The two areas of focus here are load classification and the - Conditional Throughput. - - To start with [Performance Spectrum] (#Performance-Spectrum) - subsection contains definitions needed to gain insight into what - Conditional Throughput means. Remaining subsections discuss load - classification. - - For load classification, it is useful to define *good trials* and - *bad trials*: - - * *Bad trial*: Trial is called bad (according to a goal) if its - [Trial Loss Ratio] (#Trial-Loss-Ratio) is larger than the [Goal - Loss Ratio] (#Goal-Loss-Ratio). - - * *Good trial*: Trial that is not bad is called good. - -5.2. Performance Spectrum - - ### Description - - There are several equivalent ways to explain the Conditional - Throughput computation. One of the ways relies on performance - spectrum. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 38] - -Internet-Draft MLRsearch July 2024 - - - Take an intended load value, a trial duration value, and a finite set - of trial results, with all trials measured at that load value and - duration value. - - The performance spectrum is the function that maps any non-negative - real number into a sum of trial durations among all trials in the - set, that has that number, as their trial forwarding rate, e.g. map - to zero if no trial has that particular forwarding rate. - - A related function, defined if there is at least one trial in the - set, is the performance spectrum divided by the sum of the durations - of all trials in the set. - - That function is called the performance probability function, as it - satisfies all the requirements for probability mass function of a - discrete probability distribution, the one-dimensional random - variable being the trial forwarding rate. - - These functions are related to the SUT performance spectrum, as - sampled by the trials in the set. - - Take a set of all full-length trials performed at the Relevant Lower - Bound, sorted by decreasing trial forwarding rate. The sum of the - durations of those trials may be less than the Goal Duration Sum, or - not. If it is less, add an imaginary trial result with zero trial - forwarding rate, such that the new sum of durations is equal to the - Goal Duration Sum. This is the set of trials to use. - - If the quantile touches two trials, - - the larger trial forwarding rate (from the trial result sorted - earlier) is used. - - The resulting quantity is the Conditional Throughput of the goal in - question. - - A set of examples follows. - -5.2.1. First Example - - * [Goal Exceed Ratio] (#Goal-Exceed-Ratio) = 0 and [Goal Duration - Sum] (#Goal-Duration-Sum) has been reached. - - * Conditional Throughput is the smallest trial forwarding rate among - the trials. - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 39] - -Internet-Draft MLRsearch July 2024 - - -5.2.2. Second Example - - * Goal Exceed Ratio = 0 and Goal Duration Sum has not been reached - yet. - - * Due to the missing duration sum, the worst case may still happen, - so the Conditional Throughput is zero. - - * This is not reported to the user, as this load cannot become the - Relevant Lower Bound yet. - -5.2.3. Third Example - - * Goal Exceed Ratio = 50% and Goal Duration Sum is two seconds. - - * One trial is present with the duration of one second and zero - loss. - - * The imaginary trial is added with the duration of one second and - zero trial forwarding rate. - - * The median would touch both trials, so the Conditional Throughput - is the trial forwarding rate of the one non-imaginary trial. - - * As that had zero loss, the value is equal to the offered load. - -5.2.4. Summary - - While the Conditional Throughput is a generalization of the trial - forwarding rate, its definition is not an obvious one. - - Other than the trial forwarding rate, the other source of intuition - is the quantile in general, and the median the recommended case. - -5.3. Trials with Single Duration - - When goal attributes are chosen in such a way that every trial has - the same intended duration, the load classification is simpler. - - The following description follows the motivation of Goal Loss Ratio, - Goal Exceed Ratio, and Goal Duration Sum. - - If the sum of the durations of all trials (at the given load) is less - than the Goal Duration Sum, imagine two scenarios: - - * *best case scenario*: all subsequent trials having zero loss, and - - * *worst case scenario*: all subsequent trials having 100% loss. - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 40] - -Internet-Draft MLRsearch July 2024 - - - Here we assume there are as many subsequent trials as needed to make - the sum of all trials equal to the Goal Duration Sum. - - The exceed ratio is defined using sums of durations (and number of - trials does not matter), so it does not matter whether the - "subsequent trials" can consist of an integer number of full-length - trials. - - In any of the two scenarios, best case and worst case, we can compute - the load exceed ratio, as the duration sum of good trials divided by - the duration sum of all trials, in both cases including the assumed - trials. - - Even if, in the best case scenario, the load exceed ratio is larger - than the Goal Exceed Ratio, the load is an upper bound. - - MKP2 Even if, in the worst case scenario, the load exceed ratio is - not larger than the Goal Exceed Ratio, the load is a lower bound. - - More specifically: - - * Take all trials measured at a given load. - - * The sum of the durations of all bad full-length trials is called - the bad sum. - - * The sum of the durations of all good full-length trials is called - the good sum. - - * The result of adding the bad sum plus the good sum is called the - measured sum. - - * The larger of the measured sum and the Goal Duration Sum is called - the whole sum. - - * The whole sum minus the measured sum is called the missing sum. - - * The optimistic exceed ratio is the bad sum divided by the whole - sum. - - * The pessimistic exceed ratio is the bad sum plus the missing sum, - that divided by the whole sum. - - * If the optimistic exceed ratio is larger than the Goal Exceed - Ratio, the load is classified as an upper bound. - - * If the pessimistic exceed ratio is not larger than the Goal Exceed - Ratio, the load is classified as a lower bound. - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 41] - -Internet-Draft MLRsearch July 2024 - - - * Else, the load is classified as undecided. - - The definition of pessimistic exceed ratio is compatible with the - logic in the Conditional Throughput computation, so in this single - trial duration case, a load is a lower bound if and only if the - Conditional Throughput loss ratio is not larger than the Goal Loss - Ratio. - - If it is larger, the load is either an upper bound or undecided. - -5.4. Trials with Short Duration - -5.4.1. Scenarios - - Trials with intended duration smaller than the goal final trial - duration are called short trials. The motivation for load - classification logic in the presence of short trials is based around - a counter-factual case: What would the trial result be if a short - trial has been measured as a full-length trial instead? - - There are three main scenarios where human intuition guides the - intended behavior of load classification. - -5.4.1.1. False Good Scenario - - The user had their reason for not configuring a shorter goal final - trial duration. Perhaps SUT has buffers that may get full at longer - trial durations. Perhaps SUT shows periodic decreases in performance - the user does not want to be treated as noise. - - In any case, many good short trials may become bad full-length trials - in the counter-factual case. - - In extreme cases, there are plenty of good short trials and no bad - short trials. - - In this scenario, we want the load classification NOT to classify the - load as a lower bound, despite the abundance of good short trials. - - Effectively, we want the good short trials to be ignored, so they do - not contribute to comparisons with the Goal Duration Sum. - -5.4.1.2. True Bad Scenario - - When there is a frame loss in a short trial, the counter-factual - full-length trial is expected to lose at least as many frames. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 42] - -Internet-Draft MLRsearch July 2024 - - - In practice, bad short trials are rarely turning into good full- - length trials. - - In extreme cases, there are no good short trials. - - In this scenario, we want the load classification to classify the - load as an upper bound just based on the abundance of short bad - trials. - - Effectively, we want the bad short trials to contribute to - comparisons with the Goal Duration Sum, so the load can be classified - sooner. - -5.4.1.3. Balanced Scenario - - Some SUTs are quite indifferent to trial duration. Performance - probability function constructed from short trial results is likely - to be similar to the performance probability function constructed - from full-length trial results (perhaps with larger dispersion, but - without a big impact on the median quantiles overall). - - For a moderate Goal Exceed Ratio value, this may mean there are both - good short trials and bad short trials. - - This scenario is there just to invalidate a simple heuristic of - always ignoring good short trials and never ignoring bad short - trials, as that simple heuristic would be too biased. - - Yes, the short bad trials are likely to turn into full-length bad - trials in the counter-factual case, but there is no information on - what would the good short trials turn into. - - The only way to decide safely is to do more trials at full length, - the same as in False Good Scenario. - -5.4.2. Classification Logic - - MLRsearch picks a particular logic for load classification in the - presence of short trials, but it is still RECOMMENDED to use - configurations that imply no short trials, so the possible - inefficiencies in that logic do not affect the result, and the result - has better explainability. - - With that said, the logic differs from the single trial duration case - only in different definition of the bad sum. The good sum is still - the sum across all good full-length trials. - - Few more notions are needed for defining the new bad sum: - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 43] - -Internet-Draft MLRsearch July 2024 - - - * The sum of durations of all bad full-length trials is called the - bad long sum. - - * The sum of durations of all bad short trials is called the bad - short sum. - - * The sum of durations of all good short trials is called the good - short sum. - - * One minus the Goal Exceed Ratio is called the subceed ratio. - - * The Goal Exceed Ratio divided by the subceed ratio is called the - exceed coefficient. - - * The good short sum multiplied by the exceed coefficient is called - the balancing sum. - - * The bad short sum minus the balancing sum is called the excess - sum. - - * If the excess sum is negative, the bad sum is equal to the bad - long sum. - - * Otherwise, the bad sum is equal to the bad long sum plus the - excess sum. - - Here is how the new definition of the bad sum fares in the three - scenarios, where the load is close to what would the relevant bounds - be if only full-length trials were used for the search. - -5.4.2.1. False Good Scenario - - If the duration is too short, we expect to see a higher frequency of - good short trials. This could lead to a negative excess sum, which - has no impact, hence the load classification is given just by full- - length trials. Thus, MLRsearch using too short trials has no - detrimental effect on result comparability in this scenario. But - also using short trials does not help with overall search duration, - probably making it worse. - -5.4.2.2. True Bad Scenario - - Settings with a small exceed ratio have a small exceed coefficient, - so the impact of the good short sum is small, and the bad short sum - is almost wholly converted into excess sum, thus bad short trials - have almost as big an impact as full-length bad trials. The same - conclusion applies to moderate exceed ratio values when the good - short sum is small. Thus, short trials can cause a load to get - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 44] - -Internet-Draft MLRsearch July 2024 - - - classified as an upper bound earlier, bringing time savings (while - not affecting comparability). - -5.4.2.3. Balanced Scenario - - Here excess sum is small in absolute value, as the balancing sum is - expected to be similar to the bad short sum. Once again, full-length - trials are needed for final load classification; but usage of short - trials probably means MLRsearch needed a shorter overall search time - before selecting this load for measurement, thus bringing time - savings (while not affecting comparability). - - Note that in presence of short trial results, the comparibility - between the load classification and the Conditional Throughput is - only partial. The Conditional Throughput still comes from a good - long trial, but a load higher than the Relevant Lower Bound may also - compute to a good value. - -5.5. Trials with Longer Duration - - If there are trial results with an intended duration larger than the - goal trial duration, the precise definitions in Appendix A and - Appendix B treat them in exactly the same way as trials with duration - equal to the goal trial duration. - - But in configurations with moderate (including 0.5) or small Goal - Exceed Ratio and small Goal Loss Ratio (especially zero), bad trials - with longer than goal durations may bias the search towards the lower - load values, as the noiseful end of the spectrum gets a larger - probability of causing the loss within the longer trials. - -6. IANA Considerations - - No requests of IANA. - -7. Security Considerations - - Benchmarking activities as described in this memo are limited to - technology characterization of a DUT/SUT using controlled stimuli in - a laboratory environment, with dedicated address space and the - constraints specified in the sections above. - - The benchmarking network topology will be an independent test setup - and MUST NOT be connected to devices that may forward the test - traffic into a production network or misroute traffic to the test - management network. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 45] - -Internet-Draft MLRsearch July 2024 - - - Further, benchmarking is performed on a "black-box" basis, relying - solely on measurements observable external to the DUT/SUT. - - Special capabilities SHOULD NOT exist in the DUT/SUT specifically for - benchmarking purposes. Any implications for network security arising - from the DUT/SUT SHOULD be identical in the lab and in production - networks. - -8. Acknowledgements - - Some phrases and statements in this document were created with help - of Mistral AI (mistral.ai). - - Many thanks to Alec Hothan of the OPNFV NFVbench project for thorough - review and numerous useful comments and suggestions in the earlier - versions of this document. - - Special wholehearted gratitude and thanks to the late Al Morton for - his thorough reviews filled with very specific feedback and - constructive guidelines. Thank you Al for the close collaboration - over the years, for your continuous unwavering encouragement full of - empathy and positive attitude. Al, you are dearly missed. - -9. Appendix A: Load Classification - - This section specifies how to perform the load classification. - - Any intended load value can be classified, according to a given - [Search Goal] (#Search-Goal). - - The algorithm uses (some subsets of) the set of all available trial - results from trials measured at a given intended load at the end of - the search. All durations are those returned by the Measurer. - - The block at the end of this appendix holds pseudocode which computes - two values, stored in variables named optimistic and pessimistic. - - The pseudocode happens to be a valid Python code. - - If values of both variables are computed to be true, the load in - question is classified as a lower bound according to the given Search - Goal. If values of both variables are false, the load is classified - as an upper bound. Otherwise, the load is classified as undecided. - - The pseudocode expects the following variables to hold values as - follows: - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 46] - -Internet-Draft MLRsearch July 2024 - - - * goal_duration_sum: The duration sum value of the given Search - Goal. - - * goal_exceed_ratio: The exceed ratio value of the given Search - Goal. - - * good_long_sum: Sum of durations across trials with trial duration - at least equal to the goal final trial duration and with a Trial - Loss Ratio not higher than the Goal Loss Ratio. - - * bad_long_sum: Sum of durations across trials with trial duration - at least equal to the goal final trial duration and with a Trial - Loss Ratio higher than the Goal Loss Ratio. - - * good_short_sum: Sum of durations across trials with trial duration - shorter than the goal final trial duration and with a Trial Loss - Ratio not higher than the Goal Loss Ratio. - - * bad_short_sum: Sum of durations across trials with trial duration - shorter than the goal final trial duration and with a Trial Loss - Ratio higher than the Goal Loss Ratio. - - The code works correctly also when there are no trial results at a - given load. - - balancing_sum = good_short_sum * goal_exceed_ratio / (1.0 - goal_exceed_ratio) - effective_bad_sum = bad_long_sum + max(0.0, bad_short_sum - balancing_sum) - effective_whole_sum = max(good_long_sum + effective_bad_sum, goal_duration_sum) - quantile_duration_sum = effective_whole_sum * goal_exceed_ratio - optimistic = effective_bad_sum <= quantile_duration_sum - pessimistic = (effective_whole_sum - good_long_sum) <= quantile_duration_sum - -10. Appendix B: Conditional Throughput - - This section specifies how to compute Conditional Throughput, as - referred to in section [Conditional Throughput] (#Conditional- - Throughput). - - Any intended load value can be used as the basis for the following - computation, but only the Relevant Lower Bound (at the end of the - search) leads to the value called the Conditional Throughput for a - given Search Goal. - - The algorithm uses (some subsets of) the set of all available trial - results from trials measured at a given intended load at the end of - the search. All durations are those returned by the Measurer. - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 47] - -Internet-Draft MLRsearch July 2024 - - - The block at the end of this appendix holds pseudocode which computes - a value stored as variable conditional_throughput. - - The pseudocode happens to be a valid Python code. - - The pseudocode expects the following variables to hold values as - follows: - - * goal_duration_sum: The duration sum value of the given Search - Goal. - - * goal_exceed_ratio: The exceed ratio value of the given Search - Goal. - - * good_long_sum: Sum of durations across trials with trial duration - at least equal to the goal final trial duration and with a Trial - Loss Ratio not higher than the Goal Loss Ratio. - - * bad_long_sum: Sum of durations across trials with trial duration - at least equal to the goal final trial duration and with a Trial - Loss Ratio higher than the Goal Loss Ratio. - - * long_trials: An iterable of all trial results from trials with - trial duration at least equal to the goal final trial duration, - sorted by increasing the Trial Loss Ratio. A trial result is a - composite with the following two attributes available: - - - trial.loss_ratio: The Trial Loss Ratio as measured for this - trial. - - - trial.duration: The trial duration of this trial. - - The code works correctly only when there if there is at least one - trial result measured at a given load. - - all_long_sum = max(goal_duration_sum, good_long_sum + bad_long_sum) - remaining = all_long_sum * (1.0 - goal_exceed_ratio) - quantile_loss_ratio = None - for trial in long_trials: - if quantile_loss_ratio is None or remaining > 0.0: - quantile_loss_ratio = trial.loss_ratio - remaining -= trial.duration - else: - break - else: - if remaining > 0.0: - quantile_loss_ratio = 1.0 - conditional_throughput = intended_load * (1.0 - quantile_loss_ratio) - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 48] - -Internet-Draft MLRsearch July 2024 - - -11. References - -11.1. Normative References - - [RFC1242] Bradner, S., "Benchmarking Terminology for Network - Interconnection Devices", RFC 1242, DOI 10.17487/RFC1242, - July 1991, <https://www.rfc-editor.org/info/rfc1242>. - - [RFC2285] Mandeville, R., "Benchmarking Terminology for LAN - Switching Devices", RFC 2285, DOI 10.17487/RFC2285, - February 1998, <https://www.rfc-editor.org/info/rfc2285>. - - [RFC2544] Bradner, S. and J. McQuaid, "Benchmarking Methodology for - Network Interconnect Devices", RFC 2544, - DOI 10.17487/RFC2544, March 1999, - <https://www.rfc-editor.org/info/rfc2544>. - - [RFC8219] Georgescu, M., Pislaru, L., and G. Lencse, "Benchmarking - Methodology for IPv6 Transition Technologies", RFC 8219, - DOI 10.17487/RFC8219, August 2017, - <https://www.rfc-editor.org/info/rfc8219>. - - [RFC9004] Morton, A., "Updates for the Back-to-Back Frame Benchmark - in RFC 2544", RFC 9004, DOI 10.17487/RFC9004, May 2021, - <https://www.rfc-editor.org/info/rfc9004>. - -11.2. Informative References - - [FDio-CSIT-MLRsearch] - "FD.io CSIT Test Methodology - MLRsearch", October 2023, - <https://csit.fd.io/cdocs/methodology/measurements/ - data_plane_throughput/mlr_search/>. - - [PyPI-MLRsearch] - "MLRsearch 1.2.1, Python Package Index", October 2023, - <https://pypi.org/project/MLRsearch/1.2.1/>. - - [TST009] "TST 009", n.d., <https://www.etsi.org/deliver/etsi_gs/ - NFV-TST/001_099/009/03.04.01_60/gs_NFV- - TST009v030401p.pdf>. - -Authors' Addresses - - Maciek Konstantynowicz - Cisco Systems - Email: mkonstan@cisco.com - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 49] - -Internet-Draft MLRsearch July 2024 - - - Vratko Polak - Cisco Systems - Email: vrpolak@cisco.com - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Konstantynowicz & Polak Expires 18 January 2025 [Page 50] |