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diff --git a/docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-03.md b/docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-03.md new file mode 100644 index 0000000000..d7dfa924fd --- /dev/null +++ b/docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-03.md @@ -0,0 +1,556 @@ +--- +title: Multiple Loss Ratio Search for Packet Throughput (MLRsearch) +# abbrev: MLRsearch +docname: draft-vpolak-mkonstan-bmwg-mlrsearch-03 +date: 2020-02-28 + +ipr: trust200902 +area: ops +wg: Benchmarking Working Group +kw: Internet-Draft +cat: info + +coding: us-ascii +pi: # can use array (if all yes) or hash here +# - toc +# - sortrefs +# - symrefs + toc: yes + sortrefs: # defaults to yes + symrefs: yes + +author: + - + ins: M. Konstantynowicz + name: Maciek Konstantynowicz + org: Cisco Systems + role: editor + email: mkonstan@cisco.com + - + ins: V. Polak + name: Vratko Polak + org: Cisco Systems + role: editor + email: vrpolak@cisco.com + +normative: + RFC2544: + RFC8174: + +informative: + FDio-CSIT-MLRsearch: + target: https://docs.fd.io/csit/rls2001/report/introduction/methodology_data_plane_throughput/methodology_mlrsearch_tests.html + title: "FD.io CSIT Test Methodology - MLRsearch" + date: 2020-02 + PyPI-MLRsearch: + target: https://pypi.org/project/MLRsearch/0.3.0/ + title: "MLRsearch 0.3.0, Python Package Index" + date: 2020-02 + +--- abstract + +This document proposes changes to [RFC2544], specifically to packet +throughput search methodology, by defining a new search algorithm +referred to as Multiple Loss Ratio search (MLRsearch for short). Instead +of relying on binary search with pre-set starting offered load, it +proposes a novel approach discovering the starting point in the initial +phase, and then searching for packet throughput based on defined packet +loss ratio (PLR) input criteria and defined final trial duration time. +One of the key design principles behind MLRsearch is minimizing the +total test duration and searching for multiple packet throughput rates +(each with a corresponding PLR) concurrently, instead of doing it +sequentially. + +The main motivation behind MLRsearch is the new set of challenges and +requirements posed by NFV (Network Function Virtualization), +specifically software based implementations of NFV data planes. Using +[RFC2544] in the experience of the authors yields often not repetitive +and not replicable end results due to a large number of factors that are +out of scope for this draft. MLRsearch aims to address this challenge +in a simple way of getting the same result sooner, so more repetitions +can be done to describe the replicability. + +--- middle + +# Terminology + +* Frame size: size of an Ethernet Layer-2 frame on the wire, including + any VLAN tags (dot1q, dot1ad) and Ethernet FCS, but excluding Ethernet + preamble and inter-frame gap. Measured in bytes. +* Packet size: same as frame size, both terms used interchangeably. +* Device Under Test (DUT): In software networking, "device" denotes a + specific piece of software tasked with packet processing. Such device + is surrounded with other software components (such as operating system + kernel). It is not possible to run devices without also running the + other components, and hardware resources are shared between both. For + purposes of testing, the whole set of hardware and software components + is called "system under test" (SUT). As SUT is the part of the whole + test setup performance of which can be measured by [RFC2544] methods, + this document uses SUT instead of [RFC2544] DUT. Device under test + (DUT) can be re-introduced when analysing test results using whitebox + techniques, but this document sticks to blackbox testing. +* System Under Test (SUT): System under test (SUT) is a part of the + whole test setup whose performance is to be benchmarked. The complete + test setup contains other parts, whose performance is either already + established, or not affecting the benchmarking result. +* Bi-directional throughput tests: involve packets/frames flowing in + both transmit and receive directions over every tested interface of + SUT/DUT. Packet flow metrics are measured per direction, and can be + reported as aggregate for both directions and/or separately + for each measured direction. In most cases bi-directional tests + use the same (symmetric) load in both directions. +* Uni-directional throughput tests: involve packets/frames flowing in + only one direction, i.e. either transmit or receive direction, over + every tested interface of SUT/DUT. Packet flow metrics are measured + and are reported for measured direction. +* Packet Loss Ratio (PLR): ratio of packets received relative to packets + transmitted over the test trial duration, calculated using formula: + PLR = ( pkts_transmitted - pkts_received ) / pkts_transmitted. + For bi-directional throughput tests aggregate PLR is calculated based + on the aggregate number of packets transmitted and received. +* Packet Throughput Rate: maximum packet offered load DUT/SUT forwards + within the specified Packet Loss Ratio (PLR). In many cases the rate + depends on the frame size processed by DUT/SUT. Hence packet + throughput rate MUST be quoted with specific frame size as received by + DUT/SUT during the measurement. For bi-directional tests, packet + throughput rate should be reported as aggregate for both directions. + Measured in packets-per-second (pps) or frames-per-second (fps), + equivalent metrics. +* Bandwidth Throughput Rate: a secondary metric calculated from packet + throughput rate using formula: bw_rate = pkt_rate * (frame_size + + L1_overhead) * 8, where L1_overhead for Ethernet includes preamble (8 + Bytes) and inter-frame gap (12 Bytes). For bi-directional tests, + bandwidth throughput rate should be reported as aggregate for both + directions. Expressed in bits-per-second (bps). +* Non Drop Rate (NDR): maximum packet/bandwith throughput rate sustained + by DUT/SUT at PLR equal zero (zero packet loss) specific to tested + frame size(s). MUST be quoted with specific packet size as received by + DUT/SUT during the measurement. Packet NDR measured in + packets-per-second (or fps), bandwidth NDR expressed in + bits-per-second (bps). +* Partial Drop Rate (PDR): maximum packet/bandwith throughput rate + sustained by DUT/SUT at PLR greater than zero (non-zero packet loss) + specific to tested frame size(s). MUST be quoted with specific packet + size as received by DUT/SUT during the measurement. Packet PDR + measured in packets-per-second (or fps), bandwidth PDR expressed in + bits-per-second (bps). +* Maximum Receive Rate (MRR): packet/bandwidth rate regardless of PLR + sustained by DUT/SUT under specified Maximum Transmit Rate (MTR) + packet load offered by traffic generator. MUST be quoted with both + specific packet size and MTR as received by DUT/SUT during the + measurement. Packet MRR measured in packets-per-second (or fps), + bandwidth MRR expressed in bits-per-second (bps). +* Trial: a single measurement step. See [RFC2504] section 23. +* Trial duration: amount of time over which packets are transmitted + in a single measurement step. + +# MLRsearch Background + +Multiple Loss Ratio search (MLRsearch) is a packet throughput search +algorithm suitable for deterministic systems (as opposed to +probabilistic systems). MLRsearch discovers multiple packet throughput +rates in a single search, with each rate associated with a distinct +Packet Loss Ratio (PLR) criteria. + +For cases when multiple rates need to be found, this property makes +MLRsearch more efficient in terms of time execution, compared to +traditional throughput search algorithms that discover a single packet +rate per defined search criteria (e.g. a binary search specified by +[RFC2544]). MLRsearch reduces execution time even further by relying on +shorter trial durations of intermediate steps, with only the final +measurements conducted at the specified final trial duration. This +results in the shorter overall search execution time when compared to a +traditional binary search, while guaranteeing the same results for +deterministic systems. + +In practice two rates with distinct PLRs are commonly used for packet +throughput measurements of NFV systems: Non Drop Rate (NDR) with PLR=0 +and Partial Drop Rate (PDR) with PLR>0. The rest of this document +describes MLRsearch for NDR and PDR. If needed, MLRsearch can be +adapted to discover more throughput rates with different pre-defined +PLRs. + +Similarly to other throughput search approaches like binary search, +MLRsearch is effective for SUTs/DUTs with PLR curve that is continuously +flat or increasing with growing offered load. It may not be as +effective for SUTs/DUTs with abnormal PLR curves. + +MLRsearch relies on traffic generator to qualify the received packet +stream as error-free, and invalidate the results if any disqualifying +errors are present e.g. out-of-sequence frames. + +MLRsearch can be applied to both uni-directional and bi-directional +throughput tests. + +For bi-directional tests, MLRsearch rates and ratios are aggregates of +both directions, based on the following assumptions: + +* Traffic transmitted by traffic generator and received by SUT/DUT + has the same packet rate in each direction, + in other words the offered load is symmetric. +* SUT/DUT packet processing capacity is the same in both directions, + resulting in the same packet loss under load. + +# MLRsearch Overview + +The main properties of MLRsearch: + +* MLRsearch is a duration aware multi-phase multi-rate search algorithm: + * Initial Phase determines promising starting interval for the search. + * Intermediate Phases progress towards defined final search criteria. + * Final Phase executes measurements according to the final search + criteria. + * Final search criteria are defined by following inputs: + * PLRs associated with NDR and PDR. + * Final trial duration. + * Measurement resolution. +* Initial Phase: + * Measure MRR over initial trial duration. + * Measured MRR is used as an input to the first intermediate phase. +* Multiple Intermediate Phases: + * Trial duration: + * Start with initial trial duration in the first intermediate phase. + * Converge geometrically towards the final trial duration. + * Track two values for NDR and two for PDR: + * The values are called lower_bound and upper_bound. + * Each value comes from a specific trial measurement: + * Most recent for that transmit rate. + * As such the value is associated with that measurement's duration + and loss. + * A bound can be valid or invalid: + * Valid lower_bound must conform with PLR search criteria. + * Valid upper_bound must not conform with PLR search criteria. + * Example of invalid NDR lower_bound is if it has been measured + with non-zero loss. + * Invalid bounds are not real boundaries for the searched value: + * They are needed to track interval widths. + * Valid bounds are real boundaries for the searched value. + * Each non-initial phase ends with all bounds valid. + * Bound can become invalid if it re-measured at a longer trial + duration in a sub-sequent phase. + * Search: + * Start with a large (lower_bound, upper_bound) interval width, that + determines measurement resolution. + * Geometrically converge towards the width goal of the phase. + * Each phase halves the previous width goal. + * First measurement of the next phase will be internal search + which always gives a valid bound and brings the width to the new goal. + * Only one bound then needs to be re-measured with new duration. + * Use of internal and external searches: + * External search: + * Measures at transmit rates outside the (lower_bound, + upper_bound) interval. + * Activated when a bound is invalid, to search for a new valid + bound by multiplying (for example doubling) the interval width. + * It is a variant of "exponential search". + * Internal search: + * A "binary search" that measures at transmit rates within the + (lower_bound, upper_bound) valid interval, halving the interval + width. +* Final Phase: + * Executed with the final test trial duration, and the final width + goal that determines resolution of the overall search. +* Intermediate Phases together with the Final Phase are called + Non-Initial Phases. + +The main benefits of MLRsearch vs. binary search include: + +* In general MLRsearch is likely to execute more trials overall, but + likely less trials at a set final trial duration. +* In well behaving cases, e.g. when results do not depend on trial + duration, it greatly reduces (>50%) the overall duration compared to a + single PDR (or NDR) binary search over duration, while finding + multiple drop rates. +* In all cases MLRsearch yields the same or similar results to binary + search. +* Note: both binary search and MLRsearch are susceptible to reporting + non-repeatable results across multiple runs for very bad behaving + cases. + +Caveats: + +* Worst case MLRsearch can take longer than a binary search e.g. in case of + drastic changes in behaviour for trials at varying durations. + +# Sample Implementation + +Following is a brief description of a sample MLRsearch implementation, +which is a simlified version of the existing implementation. + +## Input Parameters + +1. **maximum_transmit_rate** - Maximum Transmit Rate (MTR) of packets to + be used by external traffic generator implementing MLRsearch, + limited by the actual Ethernet link(s) rate, NIC model or traffic + generator capabilities. +2. **minimum_transmit_rate** - minimum packet transmit rate to be used for + measurements. MLRsearch fails if lower transmit rate needs to be + used to meet search criteria. +3. **final_trial_duration** - required trial duration for final rate + measurements. +4. **initial_trial_duration** - trial duration for initial MLRsearch phase. +5. **final_relative_width** - required measurement resolution expressed as + (lower_bound, upper_bound) interval width relative to upper_bound. +6. **packet_loss_ratio** - maximum acceptable PLR search criterion for + PDR measurements. +7. **number_of_intermediate_phases** - number of phases between the initial + phase and the final phase. Impacts the overall MLRsearch duration. + Less phases are required for well behaving cases, more phases + may be needed to reduce the overall search duration for worse behaving cases. + +## Initial Phase + +1. First trial measures at configured maximum transmit rate (MTR) and + discovers maximum receive rate (MRR). + * IN: trial_duration = initial_trial_duration. + * IN: offered_transmit_rate = maximum_transmit_rate. + * DO: single trial. + * OUT: measured loss ratio. + * OUT: MRR = measured receive rate. + If loss ratio is zero, MRR is set below MTR so that interval width is equal + to the width goal of the first intermediate phase. +2. Second trial measures at MRR and discovers MRR2. + * IN: trial_duration = initial_trial_duration. + * IN: offered_transmit_rate = MRR. + * DO: single trial. + * OUT: measured loss ratio. + * OUT: MRR2 = measured receive rate. + If loss ratio is zero, MRR2 is set above MRR so that interval width is equal + to the width goal of the first intermediate phase. + MRR2 could end up being equal to MTR (for example if both measurements so far + had zero loss), which was already measured, step 3 is skipped in that case. +3. Third trial measures at MRR2. + * IN: trial_duration = initial_trial_duration. + * IN: offered_transmit_rate = MRR2. + * DO: single trial. + * OUT: measured loss ratio. + +## Non-Initial Phases + +1. Main loop: + 1. IN: trial_duration for the current phase. Set to + initial_trial_duration for the first intermediate phase; to + final_trial_duration for the final phase; or to the element of + interpolating geometric sequence for other intermediate phases. + For example with two intermediate phases, trial_duration of the + second intermediate phase is the geometric average of + initial_trial_duration and final_trial_duration. + 2. IN: relative_width_goal for the current phase. Set to + final_relative_width for the final phase; doubled for each + preceding phase. For example with two intermediate phases, the + first intermediate phase uses quadruple of final_relative_width + and the second intermediate phase uses double of + final_relative_width. + 3. IN: ndr_interval, pdr_interval from the previous main loop + iteration or the previous phase. If the previous phase is the + initial phase, both intervals are formed by a (correctly ordered) + pair of MRR2 and MRR. Note that the initial phase is likely + to create intervals with invalid bounds. + 4. DO: According to the procedure described in point 2., either exit + the phase (by jumping to 1.7.), or calculate new transmit rate to + measure with. + 5. DO: Perform the trial measurement at the new transmit rate and + trial_duration, compute its loss ratio. + 6. DO: Update the bounds of both intervals, based on the new + measurement. The actual update rules are numerous, as NDR external + search can affect PDR interval and vice versa, but the result + agrees with rules of both internal and external search. For + example, any new measurement below an invalid lower_bound becomes + the new lower_bound, while the old measurement (previously acting + as the invalid lower_bound) becomes a new and valid upper_bound. + Go to next iteration (1.3.), taking the updated intervals as new + input. + 7. OUT: current ndr_interval and pdr_interval. In the final phase + this is also considered to be the result of the whole search. For + other phases, the next phase loop is started with the current + results as an input. +2. New transmit rate (or exit) calculation (for point 1.4.): + 1. If there is an invalid bound then prepare for external search: + * IF the most recent measurement at NDR lower_bound transmit + rate had the loss higher than zero, then the new transmit rate + is NDR lower_bound decreased by two NDR interval widths. + * Else, IF the most recent measurement at PDR lower_bound + transmit rate had the loss higher than PLR, then the new + transmit rate is PDR lower_bound decreased by two PDR interval + widths. + * Else, IF the most recent measurement at NDR upper_bound + transmit rate had no loss, then the new transmit rate is NDR + upper_bound increased by two NDR interval widths. + * Else, IF the most recent measurement at PDR upper_bound + transmit rate had the loss lower or equal to PLR, then the new + transmit rate is PDR upper_bound increased by two PDR interval + widths. + 2. Else, if interval width is higher than the current phase goal: + * IF NDR interval does not meet the current phase width + goal, prepare for internal search. The new transmit rate is a + in the middle of NDR lower_bound and NDR upper_bound. + * IF PDR interval does not meet the current phase width + goal, prepare for internal search. The new transmit rate is a + in the middle of PDR lower_bound and PDR upper_bound. + 3. Else, if some bound has still only been measured at a lower + duration, prepare to re-measure at the current duration (and the + same transmit rate). The order of priorities is: + * NDR lower_bound, + * PDR lower_bound, + * NDR upper_bound, + * PDR upper_bound. + 4. Else, do not prepare any new rate, to exit the phase. + This ensures that at the end of each non-initial phase + all intervals are valid, narrow enough, and measured + at current phase trial duration. + +# FD.io CSIT Implementation + +The only known working implementation of MLRsearch is in +the open-source code running in Linux Foundation +FD.io CSIT project [FDio-CSIT-MLRsearch] as part of +a Continuous Integration / Continuous Development (CI/CD) framework. + +MLRsearch is also available as a Python package in [PyPI-MLRsearch]. + +## Additional details + +This document so far has been describing a simplified version of +MLRsearch algorithm. The full algorithm as implemented in CSIT contains +additional logic, which makes some of the details (but not general +ideas) above incorrect. Here is a short description of the additional +logic as a list of principles, explaining their main differences from +(or additions to) the simplified description, but without detailing +their mutual interaction. + +1. Logarithmic transmit rate. + * In order to better fit the relative width goal, the interval + doubling and halving is done differently. + * For example, the middle of 2 and 8 is 4, not 5. +2. Optimistic maximum rate. + * The increased rate is never higher than the maximum rate. + * Upper bound at that rate is always considered valid. +3. Pessimistic minimum rate. + * The decreased rate is never lower than the minimum rate. + * If a lower bound at that rate is invalid, a phase stops refining + the interval further (until it gets re-measured). +4. Conservative interval updates. + * Measurements above the current upper bound never update a valid upper + bound, even if drop ratio is low. + * Measurements below the current lower bound always update any lower + bound if drop ratio is high. +5. Ensure sufficient interval width. + * Narrow intervals make external search take more time to find a + valid bound. + * If the new transmit increased or decreased rate would result in + width less than the current goal, increase/decrease more. + * This can happen if the measurement for the other interval + makes the current interval too narrow. + * Similarly, take care the measurements in the initial phase create + wide enough interval. +6. Timeout for bad cases. + * The worst case for MLRsearch is when each phase converges to + intervals way different than the results of the previous phase. + * Rather than suffer total search time several times larger than pure + binary search, the implemented tests fail themselves when the + search takes too long (given by argument *timeout*). +7. Pessimistic external search. + * Valid bound becoming invalid on re-measurement with higher duration + is frequently a sign of SUT behaving in non-deterministic way + (from blackbox point of view). If the final width interval goal + is too narrow compared to width of rate region where SUT + is non-deterministic, it is quite likely that there will be multiple + invalid bounds before the external search finds a valid one. + * In this case, external search can be sped up by increasing interval width + more rapidly. As only powers of two ensure the subsequent internal search + will not result in needlessly narrow interval, a parameter *doublings* + is introduced to control the pessimism of external search. + For example three doublings result in interval width being multiplied + by eight in each external search iteration. + +### FD.io CSIT Input Parameters + +1. **maximum_transmit_rate** - Typical values: 2 * 14.88 Mpps for 64B + 10GE link rate, 2 * 18.75 Mpps for 64B 40GE NIC (specific model). +2. **minimum_transmit_rate** - Value: 2 * 10 kpps (traffic generator + limitation). +3. **final_trial_duration** - Value: 30 seconds. +4. **initial_trial_duration** - Value: 1 second. +5. **final_relative_width** - Value: 0.005 (0.5%). +6. **packet_loss_ratio** - Value: 0.005 (0.5%). +7. **number_of_intermediate_phases** - Value: 2. + The value has been chosen based on limited experimentation to date. + More experimentation needed to arrive to clearer guidelines. +8. **timeout** - Limit for the overall search duration (for one search). + If MLRsearch oversteps this limit, it immediatelly declares the test failed, + to avoid wasting even more time on a misbehaving SUT. + Value: 600 (seconds). +9. **doublings** - Number of dublings when computing new interval width + in external search. + Value: 2 (interval width is quadroupled). + Value of 1 is best for well-behaved SUTs, but value of 2 has been found + to decrease overall search time for worse-behaved SUT configurations, + contributing more to the overall set of different SUT configurations tested. + +## Example MLRsearch Run + +The following table shows data from a real test run in CSIT +(using the default input values as above). +The first column is the phase, the second is the trial measurement performed +(aggregate bidirectional offered load in megapackets per second, +and trial duration in seconds). +Each of last four columns show one bound as updated after the measurement +(duration truncated to save space). +Loss ratio is not shown, but invalid bounds are marked with a plus sign. + +| Phase | Trial | NDR lower | NDR upper | PDR lower | PDR upper | +| ----: | ---------: | --------: | --------: | --------: | --------: | +| init. | 37.50 1.00 | N/A | 37.50 1. | N/A | 37.50 1. | +| init. | 10.55 1.00 | +10.55 1. | 37.50 1. | +10.55 1. | 37.50 1. | +| init. | 9.437 1.00 | +9.437 1. | 10.55 1. | +9.437 1. | 10.55 1. | +| int 1 | 6.053 1.00 | 6.053 1. | 9.437 1. | 6.053 1. | 9.437 1. | +| int 1 | 7.558 1.00 | 7.558 1. | 9.437 1. | 7.558 1. | 9.437 1. | +| int 1 | 8.446 1.00 | 8.446 1. | 9.437 1. | 8.446 1. | 9.437 1. | +| int 1 | 8.928 1.00 | 8.928 1. | 9.437 1. | 8.928 1. | 9.437 1. | +| int 1 | 9.179 1.00 | 8.928 1. | 9.179 1. | 9.179 1. | 9.437 1. | +| int 1 | 9.052 1.00 | 9.052 1. | 9.179 1. | 9.179 1. | 9.437 1. | +| int 1 | 9.307 1.00 | 9.052 1. | 9.179 1. | 9.179 1. | 9.307 1. | +| int 2 | 9.115 5.48 | 9.115 5. | 9.179 1. | 9.179 1. | 9.307 1. | +| int 2 | 9.243 5.48 | 9.115 5. | 9.179 1. | 9.243 5. | 9.307 1. | +| int 2 | 9.179 5.48 | 9.115 5. | 9.179 5. | 9.243 5. | 9.307 1. | +| int 2 | 9.307 5.48 | 9.115 5. | 9.179 5. | 9.243 5. | +9.307 5. | +| int 2 | 9.687 5.48 | 9.115 5. | 9.179 5. | 9.307 5. | 9.687 5. | +| int 2 | 9.495 5.48 | 9.115 5. | 9.179 5. | 9.307 5. | 9.495 5. | +| int 2 | 9.401 5.48 | 9.115 5. | 9.179 5. | 9.307 5. | 9.401 5. | +| final | 9.147 30.0 | 9.115 5. | 9.147 30 | 9.307 5. | 9.401 5. | +| final | 9.354 30.0 | 9.115 5. | 9.147 30 | 9.307 5. | 9.354 30 | +| final | 9.115 30.0 | +9.115 30 | 9.147 30 | 9.307 5. | 9.354 30 | +| final | 8.935 30.0 | 8.935 30 | 9.115 30 | 9.307 5. | 9.354 30 | +| final | 9.025 30.0 | 9.025 30 | 9.115 30 | 9.307 5. | 9.354 30 | +| final | 9.070 30.0 | 9.070 30 | 9.115 30 | 9.307 5. | 9.354 30 | +| final | 9.307 30.0 | 9.070 30 | 9.115 30 | 9.307 30 | 9.354 30 | + +# IANA Considerations + +No requests of IANA. + +# 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. + +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. + +# Acknowledgements + +Many thanks to Alec Hothan of OPNFV NFVbench project for thorough +review and numerous useful comments and suggestions. + +--- back |