Benchmarking Working Group M. Konstantynowicz, Ed.
Internet-Draft V. Polak, Ed.
Intended status: Informational Cisco Systems
Expires: January 13, 2022 July 12, 2021
Multiple Loss Ratio Search for Packet Throughput (MLRsearch)
draft-ietf-bmwg-mlrsearch-01
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
Konstantynowicz & Polak Expires January 13, 2022 [Page 1]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
This Internet-Draft will expire on January 13, 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. MLRsearch Background . . . . . . . . . . . . . . . . . . . . 5
3. MLRsearch Overview . . . . . . . . . . . . . . . . . . . . . 6
4. Sample Implementation . . . . . . . . . . . . . . . . . . . . 9
4.1. Input Parameters . . . . . . . . . . . . . . . . . . . . 9
4.2. Initial Phase . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Non-Initial Phases . . . . . . . . . . . . . . . . . . . 11
5. FD.io CSIT Implementation . . . . . . . . . . . . . . . . . . 15
5.1. Additional details . . . . . . . . . . . . . . . . . . . 15
5.1.1. FD.io CSIT Input Parameters . . . . . . . . . . . . . 17
5.2. Example MLRsearch Run . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . 21
9.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Terminology
o 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).
o Packet size: same as frame size, both terms used interchangeably.
Konstantynowicz & Polak Expires January 13, 2022 [Page 2]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
o 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.
o 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.
o 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.
o 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.
o 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.
o 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.
o 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.
Konstantynowicz & Polak Expires January 13, 2022 [Page 3]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
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.
o 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.
o 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).
o 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).
o 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).
o 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).
o Trial: a single measurement step. See [RFC2544] section 23.
o Trial duration: amount of time over which packets are transmitted
in a single measurement step.
Konstantynowicz & Polak Expires January 13, 2022 [Page 4]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
2. 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:
o 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.
o SUT/DUT packet processing capacity is the same in both directions,
resulting in the same packet loss under load.
Konstantynowicz & Polak Expires January 13, 2022 [Page 5]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
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.
3. MLRsearch Overview
The main properties of MLRsearch:
o 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.
o Initial Phase:
* Measure MRR over initial trial duration.
* Measured MRR is used as an input to the first intermediate
phase.
o Multiple Intermediate Phases:
* Trial duration:
+ Start with initial trial duration in the first intermediate
phase.
+ Converge geometrically towards the final trial duration.
Konstantynowicz & Polak Expires January 13, 2022 [Page 6]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
* 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:
Konstantynowicz & Polak Expires January 13, 2022 [Page 7]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
+ 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.
o The idea is to avoid returning interval narrower than
the current width goal. See sample implementation
details, below.
o Final Phase:
* Executed with the final test trial duration, and the final
width goal that determines resolution of the overall search.
o Intermediate Phases together with the Final Phase are called Non-
Initial Phases.
o 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:
o In general MLRsearch is likely to execute more trials overall, but
likely less trials at a set final trial duration.
o 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.
o In all cases MLRsearch yields the same or similar results to
binary search.
Konstantynowicz & Polak Expires January 13, 2022 [Page 8]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
o Note: both binary search and MLRsearch are susceptible to
reporting non-repeatable results across multiple runs for very bad
behaving cases.
Caveats:
o 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.
4. Sample Implementation
Following is a brief description of a sample MLRsearch
implementation, which is a simplified version of the existing
implementation.
4.1. 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
Konstantynowicz & Polak Expires January 13, 2022 [Page 9]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
phases may be needed to reduce the overall search duration for
worse behaving cases.
4.2. 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
Konstantynowicz & Polak Expires January 13, 2022 [Page 10]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
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.
4.3. 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.
Konstantynowicz & Polak Expires January 13, 2022 [Page 11]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
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:
Konstantynowicz & Polak Expires January 13, 2022 [Page 12]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
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.
Konstantynowicz & Polak Expires January 13, 2022 [Page 13]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
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.
Konstantynowicz & Polak Expires January 13, 2022 [Page 14]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
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.
5. 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].
5.1. 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.
Konstantynowicz & Polak Expires January 13, 2022 [Page 15]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
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.
Konstantynowicz & Polak Expires January 13, 2022 [Page 16]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
* 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.
5.1.1. 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%).
Konstantynowicz & Polak Expires January 13, 2022 [Page 17]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
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.
5.2. Example MLRsearch Run
The following list describes a search from a real test run in CSIT
(using the default input values as above).
o 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).
o 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).
Konstantynowicz & Polak Expires January 13, 2022 [Page 18]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
o Both intervals are narrow enough.
o 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).
o 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).
o 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).
o Also PDR interval is narrow enough, with valid bounds for this
duration.
o 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).
o 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).
Konstantynowicz & Polak Expires January 13, 2022 [Page 19]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
Measurement 16, intended load 5190360.904111567 (re-measuring PDR
lower bound), measured loss ratio 0.0027629971184465604 (still valid
PDR lower bound).
o PDR interval is also narrow enough.
o Returning bounds:
o NDR_LOWER = 5112894.3238511775 pps; NDR_UPPER = 5138587.208637197
pps;
o PDR_LOWER = 5190360.904111567 pps; PDR_UPPER = 5216443.04126728
pps.
6. IANA Considerations
No requests of IANA.
7. 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.
8. Acknowledgements
Many thanks to Alec Hothan of OPNFV NFVbench project for thorough
review and numerous useful comments and suggestions.
9. References
Konstantynowicz & Polak Expires January 13, 2022 [Page 20]
Internet-DraMultiple Loss Ratio Search for Packet Throughput July 2021
9.1. Normative References
[RFC2544] Bradner, S. and J. McQuaid, "Benchmarking Methodology for
Network Interconnect Devices", RFC 2544,
DOI 10.17487/RFC2544, March 1999,
<https://www.rfc-editor.org/info/rfc2544>.
9.2. Informative References
[FDio-CSIT-MLRsearch]
"FD.io CSIT Test Methodology - MLRsearch", February 2021,
<https://docs.fd.io/csit/rls2101/report/introduction/
methodology_data_plane_throughput/
methodology_mlrsearch_tests.html>.
[PyPI-MLRsearch]
"MLRsearch 0.4.0, Python Package Index", April 2021,
<https://pypi.org/project/MLRsearch/0.4.0/>.
Authors' Addresses
Maciek Konstantynowicz (editor)
Cisco Systems
Email: mkonstan@cisco.com
Vratko Polak (editor)
Cisco Systems
Email: vrpolak@cisco.com
Konstantynowicz & Polak Expires January 13, 2022 [Page 21]
