diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-01.md | 362 | ||||
| -rw-r--r-- | docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-02.md | 488 |
2 files changed, 488 insertions, 362 deletions
diff --git a/docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-01.md b/docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-01.md deleted file mode 100644 index 561365ef2e..0000000000 --- a/docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-01.md +++ /dev/null @@ -1,362 +0,0 @@ ---- -title: Multiple Loss Ratio Search for Packet Throughput (MLRsearch) -# abbrev: MLRsearch -docname: draft-vpolak-mkonstan-bmwg-mlrsearch-01 -date: 2019-03-27 - -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: - - ---- 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 and -define a common (standard?) way to evaluate NFV packet throughput -performance that takes into account varying characteristics of NFV -systems under test. - ---- middle - -# Terminology - -* NDR - Non-Drop Rate, a packet throughput metric with Packet Loss Ratio - equal zero (a zero packet loss), expressed in packets-per-second - (pps). NDR packet throughput has an associated metric oftentimes - referred to as NDR bandwidth expressed in bits-per-second (bps), and - calculated as a product of: - * NDR packet rate for specific packet (frame) size, and - * Packet (L2 frame size) size in bits plus any associated L1 overhead. -* PLR - Packet Loss Ratio, a packet loss metric calculated as a ratio of - (packets_transmitted - packets_received) to packets_transmitted, over - the test trial duration. -* PDR - Partial-Drop Rate, a packet throughput metric with Packet Loss - Ratio greater than zero (a non-zero packet loss), expressed in - packets-per-second (pps). PDR packet throughput has an associated - metric oftentimes referred to as PDR bandwidth expressed in bits-per- - second (bps), and calculated as a product of: - * PDR packet rate for specific packet (frame) size, and - * Packet (L2 frame size) size in bits plus any associated L1 overhead. - -# MLRsearch Background - -Multiple Loss Rate search (MLRsearch) is a packet throughput search -algorithm suitable for deterministic (as opposed to probabilistic) -systems. MLRsearch discovers multiple packet throughput rates in a -single search, each rate associated with a distinct Packet Loss Ratio -(PLR) criteria. - -Two popular names for particular PLR criteria are Non-Drop Rate (NDR, -with PLR=0, zero packet loss) and Partial Drop Rate (PDR, with PLR>0, -non-zero packet loss). MLRsearch discovers NDR and PDR in a single -search reducing required execution time compared to separate binary -searches for NDR and PDR. 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 standard NDR/PDR binary search, while guaranteeing the same or -similar results. -(TODO: Specify "standard" in the previous sentence.) - -If needed, MLRsearch can be easily adopted to discover more throughput -rates with different pre-defined PLRs. - -Unless otherwise noted, all throughput rates are *always* bi-directional -aggregates of two equal (symmetric) uni-directional packet rates -received and reported by an external traffic generator. - -# 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. -* Initial phase: - * Uses link rate as a starting transmit rate and discovers the Maximum - Receive Rate (MRR) used as an input to the first intermediate phase. -* Intermediate phases: - * Start with initial trial duration (in the first phase) and converge - geometrically towards the final trial duration (in the final phase). - * Track two values for NDR and two for PDR. - * The values are called (NDR or PDR) lower_bound and upper_bound. - * Each value comes from a specific trial measurement - (most recent for that transmit rate), - and as such the value is associated with that measurement's duration and loss. - * A bound can be invalid, for example if NDR lower_bound - has been measured with nonzero loss. - * Invalid bounds are not real boundaries for the searched value, - but are needed to track interval widths. - * Valid bounds are real boundaries for the searched value. - * Each non-initial phase ends with all bounds valid. - * Start with a large (lower_bound, upper_bound) interval width and - geometrically converge towards the width goal (measurement resolution) - of the phase. Each phase halves the previous width goal. - * Use 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 doubling the interval width. - It is a variant of "exponential search". - * Internal search - "binary search", 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 search trials overall, but - less trials at a set final duration. -* In well behaving cases it greatly reduces (>50%) the overall duration - compared to a single PDR (or NDR) binary search 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 -based on the open-source code running in FD.io CSIT project as part of a -Continuous Integration / Continuous Development (CI/CD) framework. - -## Input Parameters - -1. **maximum_transmit_rate** - maximum packet transmit rate to be used by - external traffic generator, limited by either the actual Ethernet - link rate or traffic generator NIC model capabilities. Sample - defaults: 2 * 14.88 Mpps for 64B 10GE link rate, - 2 * 18.75 Mpps for 64B 40GE NIC maximum rate. -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. Default: 2 * 10 kpps (could be higher). -3. **final_trial_duration** - required trial duration for final rate - measurements. Default: 30 sec. -4. **initial_trial_duration** - trial duration for initial MLRsearch phase. - Default: 1 sec. -5. **final_relative_width** - required measurement resolution expressed as - (lower_bound, upper_bound) interval width relative to upper_bound. - Default: 0.5%. -6. **packet_loss_ratio** - maximum acceptable PLR search criteria for - PDR measurements. Default: 0.5%. -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. - Default (2). (Value chosen based on limited experimentation to date. - More experimentation needed to arrive to clearer guidelines.) - -## Initial phase - -1. First trial measures at maximum rate and discovers 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. -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. -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: - * *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_strial_duration and final_trial_duration. - * *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. - * *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 have - lower_bound = MRR2, uper_bound = MRR. - Note that the initial phase is likely to create intervals with invalid bounds. - * *do*: According to the procedure described in point 2, - either exit the phase (by jumping to 1.g.), - or prepare new transmit rate to measure with. - * *do*: Perform the trial measurement at the new transmit rate - and trial_duration, compute its loss ratio. - * *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.c.), taking the updated intervals as new input. - * *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 1.d.): - * 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. - * If interval width is higher than the current phase goal: - * Else, *if* NDR interval does not meet the current phase width goal, - prepare for internal search. The new transmit rate is - (NDR lower bound + NDR upper bound) / 2. - * Else, *if* PDR interval does not meet the current phase width goal, - prepare for internal search. The new transmit rate is - (PDR lower bound + PDR upper bound) / 2. - * 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. - * *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. - -# Known Implementations - -The only known working implementation of MLRsearch is in Linux Foundation -FD.io CSIT project. https://wiki.fd.io/view/CSIT. https://git.fd.io/csit/. - -## FD.io CSIT Implementation Deviations - -This document so far has been describing a simplified version of MLRsearch algorithm. -The full algorithm as implemented 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 current upper bound never update a valid upper bound, - even if drop ratio is low. - Measurements below 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*). - -# IANA Considerations - -.. - -# Security Considerations - -.. - -# Acknowledgements - -.. - ---- back diff --git a/docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-02.md b/docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-02.md new file mode 100644 index 0000000000..b80f7eda36 --- /dev/null +++ b/docs/ietf/draft-vpolak-mkonstan-bmwg-mlrsearch-02.md @@ -0,0 +1,488 @@ +--- +title: Multiple Loss Ratio Search for Packet Throughput (MLRsearch) +# abbrev: MLRsearch +docname: draft-vpolak-mkonstan-bmwg-mlrsearch-02 +date: 2019-07-08 + +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/rls1904/report/introduction/methodology_data_plane_throughput/methodology_mlrsearch_tests.html + title: "FD.io CSIT Test Methodology - MLRsearch" + date: 2019-06 + PyPI-MLRsearch: + target: https://pypi.org/project/MLRsearch/ + title: MLRsearch 0.2.0, Python Package Index + date: 2018-08 + +--- 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 and +define a common (standard?) way to evaluate NFV packet throughput +performance that takes into account varying characteristics of NFV +systems under test. + +--- 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. +* Inner L2 size: for tunneled L2 frames only, size of an encapsulated + Ethernet Layer-2 frame, preceded with tunnel header, and followed by + tunnel trailer. Measured in Bytes. +* Inner IP size: for tunneled IP packets only, size of an encapsulated + IPv4 or IPv6 packet, preceded with tunnel header, and followed by + tunnel trailer. Measured in Bytes. +* 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 + methodology 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 (i.e. throughput) and/or + separately for each measured direction (i.e. latency). 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. +* Trial duration: amount of time over which packets are transmitted and + received in a single throughput 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 easily +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: + +* Packet rates transmitted by traffic generator and received by SUT/DUT + are the same in each direction, in other words the 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 is 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 longer trial + duration in 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. + * 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 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 +based on the open-source code running in FD.io CSIT project as part of a +Continuous Integration / Continuous Development (CI/CD) framework. + +## 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. Sample defaults: 2 * 14.88 Mpps for 64B + 10GE link rate, 2 * 18.75 Mpps for 64B 40GE NIC (specific model) + maximum rate (lower than 2 * 59.52 Mpps 40GE link rate). +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. Default: 2 * 10 kpps (could be higher). +3. **final_trial_duration** - required trial duration for final rate + measurements. Default: 30 sec. +4. **initial_trial_duration** - trial duration for initial MLRsearch phase. + Default: 1 sec. +5. **final_relative_width** - required measurement resolution expressed as + (lower_bound, upper_bound) interval width relative to upper_bound. + Default: 0.5%. +6. **packet_loss_ratio** - maximum acceptable PLR search criteria for + PDR measurements. Default: 0.5%. +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. + Default (2). (Value chosen based on limited experimentation to date. + More experimentation needed to arrive to clearer guidelines.) + +## 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. +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. +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 have lower_bound = MRR2, upper_bound + = 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 or the + amount needed to hit the current width goal, whichever is + larger. + * 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. If interval width is higher than the current phase goal: + * Else, IF NDR interval does not meet the current phase width + goal, prepare for internal search. The new transmit rate is a + geometric average of NDR lower_bound and NDR upper_bound. + * Else, IF PDR interval does not meet the current phase width + goal, prepare for internal search. The new transmit rate is a + geometric average 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. + +## Sample MLRsearch Run + +TODO add a sample MLRsearch run with values. + +# Known Implementations + +The only known working implementation of MLRsearch is in Linux +Foundation FD.io CSIT project [FDio-CSIT-MLRsearch]. MLRsearch is also +available as a Python package in [PyPI-MLRsearch]. + +## FD.io CSIT Implementation Deviations + +This document so far has been describing a simplified version of +MLRsearch algorithm. The full algorithm as implemented 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 current upper bound never update a valid upper + bound, even if drop ratio is low. + * Measurements below 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*). + +# 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 |