Update of draft-vpolak-mkonstan-bmwg-mlrsearch-01->02.

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+---
+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