+++ /dev/null
----
-title: Multiple Loss Ratio Search for Packet Throughput (MLRsearch)
-# abbrev: MLRsearch
-docname: draft-ietf-bmwg-mlrsearch-00
-date: 2021-02-05
-
-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 [RFC2544] 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
--- /dev/null
+---
+title: Multiple Loss Ratio Search for Packet Throughput (MLRsearch)
+# abbrev: MLRsearch
+docname: draft-ietf-bmwg-mlrsearch-01
+date: 2021-07-12
+
+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:
+
+informative:
+ FDio-CSIT-MLRsearch:
+ target: https://docs.fd.io/csit/rls2101/report/introduction/methodology_data_plane_throughput/methodology_mlrsearch_tests.html
+ title: "FD.io CSIT Test Methodology - MLRsearch"
+ date: 2021-02
+ PyPI-MLRsearch:
+ target: https://pypi.org/project/MLRsearch/0.4.0/
+ title: "MLRsearch 0.4.0, Python Package Index"
+ date: 2021-04
+
+--- 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 (octets).
+* 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.
+* Effective loss ratio: A corrected value of measured packet loss ratio
+ chosen to avoid difficulties if SUT exhibits decreasing loss
+ with increasing load. Maximum of packet loss ratios measured at the same
+ duration on all loads smaller than (and including) the current one.
+* Target loss ratio: A packet loss ratio value acting as an imput for search.
+ The search is finding tight enough lower and upper bound in intended load,
+ so that the lower bound has smaller or equal loss ratio, and upper bound
+ has strictly larger loss ratio. For the tighterst upper bound,
+ the effective loss ratio is the same as packet loss ratio.
+ For the tightest lower bound, the effective loss ratio can be higher
+ than the packet loss ratio, but still not larger than the target loss ratio.
+* 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
+ octets) and inter-frame gap (12 octets). 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 [RFC2544] 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, each rate is associated with a distinct
+Packet Loss Ratio (PLR) criterion.
+
+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 with NDR and PDR pair as an example.
+
+Similarly to other throughput search approaches like binary search,
+MLRsearch is effective for SUTs/DUTs with PLR curve that is
+non-decreasing with growing offered load. It may not be as
+effective for SUTs/DUTs with abnormal PLR curves, although
+it will always converge to some value.
+
+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 can be applied even without those assumptions,
+but in that case the aggregate loss ratio is less useful as a metric.
+
+MLRsearch can be used for network transactions consisting of more than
+just one packet, or anything else that has intended load as input
+and loss ratio as output (duration as input is optional).
+This text uses mostly packet-centric language.
+
+# 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:
+ * Target PLRs (e.g. 0.0 and 0.005 when searching for 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 all previous trial measurement results:
+ * Duration, offered load and loss ratio are tracked.
+ * Effective loss ratios are tracked.
+ * While in practice, real loss ratios can decrease with increasing load,
+ effective loss ratios never decrease. This is achieved by sorting
+ results by load, and using the effective loss ratio of the previous load
+ if the current loss ratio is smaller than that.
+ * The algorithm queries the results to find best lower and upper bounds.
+ * Effective loss ratios are always used.
+ * The phase ends if all target loss ratios have tight enough bounds.
+ * Search:
+ * Iterate over target loss ratios in increasing order.
+ * If both upper and lower bound are in measurement results for this duration,
+ apply bisect until the bounds are tight enough,
+ and continue with next loss ratio.
+ * If a bound is missing for this duration, but there exists a bound
+ from the previous duration (compatible with the other bound
+ at this duration), re-measure at the current duration.
+ * If a bound in one direction (upper or lower) is missing for this duration,
+ and the previous duration does not have a compatible bound,
+ compute the current "interval size" from the second tightest bound
+ in the other direction (lower or upper respectively)
+ for the current duration, and choose next offered load for external search.
+ * The logic guarantees that a measurement is never repeated with both
+ duration and offered load being the same.
+ * The logic guarantees that measurements for higher target loss ratio
+ iterations (still within the same phase duration) do not affect validity
+ and tightness of bounds for previous target loss ratio iterations
+ (at the same duration).
+ * Use of internal and external searches:
+ * External search:
+ * It is a variant of "exponential search".
+ * The "interval size" is multiplied by a configurable constant
+ (powers of two work well with the subsequent internal search).
+ * Internal search:
+ * A variant of binary search that measures at offered load between
+ the previously found bounds.
+ * The interval does not need to be split into exact halves,
+ if other split can get to the target width goal faster.
+ * The idea is to avoid returning interval narrower than the current
+ width goal. See sample implementation details, below.
+* 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 returned bounds stay within prescribed min_rate and max_rate.
+ * When returning min_rate or max_rate, the returned bounds may be invalid.
+ * E.g. upper bound at max_rate may come from a measurement
+ with loss ratio still not higher than the target loss ratio.
+
+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.
+ * Re-measurement at higher duration can trigger a long external search.
+ That never happens in binary search, which uses the final duration
+ from the start.
+
+# Sample Implementation
+
+Following is a brief description of a sample MLRsearch implementation,
+which is a simplified version of the existing implementation.
+
+## Input Parameters
+
+1. **max_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. **min_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_ratios** - list of maximum acceptable PLR search criteria.
+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.
+ Received rate is computed as intended load multiplied by pass ratio
+ (which is one minus loss ratio). This is useful when loss ratio is computed
+ from a different metric than intended load. For example, intended load
+ can be in transactions (multiple packets each), but loss ratio is computed
+ on level of packets, not transactions.
+
+ * Example: If MTR is 10 transactions per second, and each transaction has
+ 10 packets, and receive rate is 90 packets per second, then loss rate
+ is 10%, and MRR is computed to be 9 transactions per second.
+
+ If MRR is too close to MTR, MRR is set below MTR so that interval width
+ is equal to the width goal of the first intermediate phase.
+ If MRR is less than min_rate, min_rate is used.
+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 MRR2 is less than min_rate, min_rate is used.
+ If loss ratio is less or equal to the smallest target loss ratio,
+ MRR2 is set to a value 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.
+ * OUT: MRR3 = measured receive rate.
+ If MRR3 is less than min_rate, min_rate is used.
+ If step 3 is not skipped, the first trial measurement is forgotten.
+ This is done because in practice (if MRR2 is above MRR), external search
+ from MRR and MRR2 is likely to lead to a faster intermediate phase
+ than a bisect between MRR2 and MTR.
+
+## Non-Initial Phases
+
+1. Main phase 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: Measurement results from the previous phase (previous duration).
+ 4. Internal target ratio loop:
+ 1. IN: Target loss ratio for this iteration of ratio loop.
+ 2. IN: Measurement results from all previous ratio loop iterations
+ of current phase (current duration).
+ 3. DO: According to the procedure described in point 2:
+ 1. either exit the phase (by jumping to 1.5),
+ 2. or exit loop iteration (by continuing with next target loss ratio,
+ jumping to 1.4.1),
+ 3. or calculate new transmit rate to measure with.
+ 4. DO: Perform the trial measurement at the new transmit rate and
+ current trial duration, compute its loss ratio.
+ 5. DO: Add the result and go to next iteration (1.4.1),
+ including the added trial result in 1.4.2.
+ 5. OUT: Measurement results from this phase.
+ 6. OUT: In the final phase, bounds for each target loss ratio
+ are extracted and returned.
+ 1. If a valid bound does not exist, use min_rate or max_rate.
+2. New transmit rate (or exit) calculation (for point 1.4.3):
+ 1. If the previous duration has the best upper and lower bound,
+ select the middle point as the new transmit rate.
+ 1. See 2.5.3. below for the exact splitting logic.
+ 2. This can be a no-op if interval is narrow enough already,
+ in that case continue with 2.2.
+ 3. Discussion, assuming the middle point is selected and measured:
+ 1. Regardless of loss rate measured, the result becomes
+ either best upper or best lower bound at current duration.
+ 2. So this condition is satisfied at most once per iteration.
+ 3. This also explains why previous phase has double width goal:
+ 1. We avoid one more bisection at previous phase.
+ 2. At most one bound (per iteration) is re-measured
+ with current duration.
+ 3. Each re-measurement can trigger an external search.
+ 4. Such surprising external searches are the main hurdle
+ in achieving low overal search durations.
+ 5. Even without 1.1, there is at most one external search
+ per phase and target loss ratio.
+ 6. But without 1.1 there can be two re-measurements,
+ each coming with a risk of triggering external search.
+ 2. If the previous duration has one bound best, select its transmit rate.
+ In deterministic case this is the last measurement needed this iteration.
+ 3. If only upper bound exists in current duration results:
+ 1. This can only happen for the smallest target loss ratio.
+ 2. If the upper bound was measured at min_rate,
+ exit the whole phase early (not investigating other target loss ratios).
+ 3. Select new transmit rate using external search:
+ 1. For computing previous interval size, use:
+ 1. second tightest bound at current duration,
+ 2. or tightest bound of previous duration,
+ if compatible and giving a more narrow interval,
+ 3. or target interval width if none of the above is available.
+ 4. In any case increase to target interval width if smaller.
+ 2. Quadruple the interval width.
+ 3. Use min_rate if the new transmit rate is lower.
+ 4. If only lower bound exists in current duration results:
+ 1. If the lower bound was measured at max_rate,
+ exit this iteration (continue with next lowest target loss ratio).
+ 2. Select new transmit rate using external search:
+ 1. For computing previous interval size, use:
+ 1. second tightest bound at current duration,
+ 2. or tightest bound of previous duration,
+ if compatible and giving a more narrow interval,
+ 3. or target interval width if none of the above is available.
+ 4. In any case increase to target interval width if smaller.
+ 2. Quadruple the interval width.
+ 3. Use max_rate if the new transmit rate is higher.
+ 5. The only remaining option is both bounds in current duration results.
+ 1. This can happen in two ways, depending on how the lower bound
+ was chosen.
+ 1. It could have been selected for the current loss ratio,
+ e.g. in re-measurement (2.2) or in initial bisect (2.1).
+ 2. It could have been found as an upper bound for the previous smaller
+ target loss ratio, in which case it might be too low.
+ 3. The algorithm does not track which one is the case,
+ as the decision logic works well regardless.
+ 2. Compute "extending down" candidate transmit rate exactly as in 2.3.
+ 3. Compute "bisecting" candidate transmit rate:
+ 1. Compute the current interval width from the two bounds.
+ 2. Express the width as a (float) multiple of the target width goal
+ for this phase.
+ 3. If the multiple is not higher than one, it means the width goal
+ is met. Exit this iteration and continue with next higher
+ target loss ratio.
+ 4. If the multiple is two or less, use half of that
+ for new width if the lower subinterval.
+ 5. Round the multiple up to nearest even integer.
+ 6. Use half of that for new width if the lower subinterval.
+ 7. Example: If lower bound is 2.0 and upper bound is 5.0, and width
+ goal is 1.0, the new candidate transmit rate will be 4.0.
+ This can save a measurement when 4.0 has small loss.
+ Selecting the average (3.5) would never save a measurement,
+ giving more narrow bounds instead.
+ 4. If either candidate computation want to exit the iteration,
+ do as bisecting candidate computation says.
+ 5. The remaining case is both candidates wanting to measure at some rate.
+ Use the higher rate. This prefers external search down narrow enough
+ interval, competing with perfectly sized lower bisect subinterval.
+
+# 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. 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*).
+3. Intended count.
+ * The number of packets to send during the trial should be equal to
+ the intended load multiplied by the duration.
+ * Also multiplied by a coefficient, if loss ratio is calculated
+ from a different metric.
+ * Example: If a successful transaction uses 10 packets,
+ load is given in transactions per second, byt loss ratio is calculated
+ from packets, the coefficient to get intended count of packets is 10.
+ * But in practice that does not work.
+ * It could result in a fractional number of packets,
+ * so it has to be rounded in a way traffic generator chooses,
+ * which may depend on the number of traffic flows
+ and traffic generator worker threads.
+4. Attempted count. As the real number of intended packets is not known exactly,
+ the computation uses the number of packets traffic generator reports as sent.
+ Unless overriden by the next point.
+5. Duration stretching.
+ * In some cases, traffic generator may get overloaded,
+ causing it to take significantly longer (than duration) to send all packets.
+ * The implementation uses an explicit stop,
+ * causing lower attempted count in those cases.
+ * The implementation tolerates some small difference between
+ attempted count and intended count.
+ * 10 microseconds worth of traffic is sufficient for our tests.
+ * If the difference is higher, the unsent packets are counted as lost.
+ * This forces the search to avoid the regions of high duration stretching.
+ * The final bounds describe the performance of not just SUT,
+ but of the whole system, including the traffic generator.
+6. Excess packets.
+ * In some test (e.g. using TCP flows) Traffic generator reacts to packet loss
+ by retransmission. Usually, such packet loss is already affecting loss ratio.
+ If a test also wants to treat retransmissions due to heavily delayed packets
+ also as a failure, this is once again visible as a mismatch between
+ the intended count and the attempted count.
+ * The CSIT implementation simply looks at absolute value of the difference,
+ so it offes the same small tolerance before it start marking a "loss".
+7. For result processing, we use lower bounds and ignore upper bounds.
+
+### FD.io CSIT Input Parameters
+
+1. **max_rate** - Typical values: 2 * 14.88 Mpps for 64B
+ 10GE link rate, 2 * 18.75 Mpps for 64B 40GE NIC (specific model).
+2. **min_rate** - Value: 2 * 9001 pps (we reserve 9000 pps
+ for latency measurements).
+3. **final_trial_duration** - Value: 30.0 seconds.
+4. **initial_trial_duration** - Value: 1.0 second.
+5. **final_relative_width** - Value: 0.005 (0.5%).
+6. **packet_loss_ratios** - Value: 0.0, 0.005 (0.0% for NDR, 0.5% for PDR).
+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: 600.0 (seconds).
+9. **expansion_coefficient** - Width multiplier for external search.
+ Value: 4.0 (interval width is quadroupled).
+ Value of 2.0 is best for well-behaved SUTs, but value of 4.0 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 list describes a search from a real test run in CSIT
+(using the default input values as above).
+
+* Initial phase, trial duration 1.0 second.
+
+Measurement 1, intended load 18750000.0 pps (MTR),
+measured loss ratio 0.7089514628479618 (valid upper bound for both NDR and PDR).
+
+Measurement 2, intended load 5457160.071600716 pps (MRR),
+measured loss ratio 0.018650817320118702 (new tightest upper bounds).
+
+Measurement 3, intended load 5348832.933500009 pps (slightly less than MRR2
+in preparation for first intermediate phase target interval width),
+measured loss ratio 0.00964383362905351 (new tightest upper bounds).
+
+* First intermediate phase starts, trial duration still 1.0 seconds.
+
+Measurement 4, intended load 4936605.579021453 pps (no lower bound,
+performing external search downwards, for NDR),
+measured loss ratio 0.0 (valid lower bound for both NDR and PDR).
+
+Measurement 5, intended load 5138587.208637197 pps (bisecting for NDR),
+measured loss ratio 0.0 (new tightest lower bounds).
+
+Measurement 6, intended load 5242656.244044665 pps (bisecting),
+measured loss ratio 0.013523745379347257 (new tightest upper bounds).
+
+* Both intervals are narrow enough.
+* Second intermediate phase starts, trial duration 5.477225575051661 seconds.
+
+Measurement 7, intended load 5190360.904111567 pps (initial bisect for NDR),
+measured loss ratio 0.0023533920869969953 (NDR upper bound, PDR lower bound).
+
+Measurement 8, intended load 5138587.208637197 pps (re-measuring NDR lower bound),
+measured loss ratio 1.2080222912800403e-06 (new tightest NDR upper bound).
+
+* The two intervals have separate bounds from now on.
+
+Measurement 9, intended load 4936605.381062318 pps (external NDR search down),
+measured loss ratio 0.0 (new valid NDR lower bound).
+
+Measurement 10, intended load 5036583.888432355 pps (NDR bisect),
+measured loss ratio 0.0 (new tightest NDR lower bound).
+
+Measurement 11, intended load 5087329.903232804 pps (NDR bisect),
+measured loss ratio 0.0 (new tightest NDR lower bound).
+
+* NDR interval is narrow enough, PDR interval not ready yet.
+
+Measurement 12, intended load 5242656.244044665 pps (re-measuring PDR upper bound),
+measured loss ratio 0.0101174866190136 (still valid PDR upper bound).
+
+* Also PDR interval is narrow enough, with valid bounds for this duration.
+* Final phase starts, trial duration 30.0 seconds.
+
+Measurement 13, intended load 5112894.3238511775 pps (initial bisect for NDR),
+measured loss ratio 0.0 (new tightest NDR lower bound).
+
+Measurement 14, intended load 5138587.208637197 (re-measuring NDR upper bound),
+measured loss ratio 2.030389804256833e-06 (still valid PDR upper bound).
+
+* NDR interval is narrow enough, PDR interval not yet.
+
+Measurement 15, intended load 5216443.04126728 pps (initial bisect for PDR),
+measured loss ratio 0.005620871287975237 (new tightest PDR upper bound).
+
+Measurement 16, intended load 5190360.904111567 (re-measuring PDR lower bound),
+measured loss ratio 0.0027629971184465604 (still valid PDR lower bound).
+
+* PDR interval is also narrow enough.
+* Returning bounds:
+* NDR_LOWER = 5112894.3238511775 pps; NDR_UPPER = 5138587.208637197 pps;
+* PDR_LOWER = 5190360.904111567 pps; PDR_UPPER = 5216443.04126728 pps.
+
+# 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
Code Review / csit.git / commitdiff