+++ /dev/null
----
-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
--- /dev/null
+---
+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
Code Review / csit.git / commitdiff