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authorMaciek Konstantynowicz <mkonstan@cisco.com>2021-02-03 14:37:01 +0000
committerMaciek Konstantynowicz <mkonstan@cisco.com>2021-02-08 20:28:55 +0000
commita82dcd874cef79388e85383cb6c0784c14e8ae7b (patch)
tree921ac28e52b99618fbf2b0875832de9db11c49e3 /docs/report/introduction/methodology_packet_latency.rst
parent127eb76dfeca04e123b0d7cc229c4a71ee3f2f9a (diff)
report: Update packet latency methodology
Change-Id: I0378e96c6f64a1dd035d56465710b82f64dc4d32 Signed-off-by: Maciek Konstantynowicz <mkonstan@cisco.com>
Diffstat (limited to 'docs/report/introduction/methodology_packet_latency.rst')
-rw-r--r--docs/report/introduction/methodology_packet_latency.rst44
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diff --git a/docs/report/introduction/methodology_packet_latency.rst b/docs/report/introduction/methodology_packet_latency.rst
index 1f7ad7f633..d5486786b6 100644
--- a/docs/report/introduction/methodology_packet_latency.rst
+++ b/docs/report/introduction/methodology_packet_latency.rst
@@ -1,33 +1,41 @@
Packet Latency
--------------
-TRex Traffic Generator (TG) is used for measuring latency across 2-Node
-and 3-Node SUT server topologies. TRex integrates `A High Dynamic Range
-Histogram (HDRH) <http://hdrhistogram.org/>`_ code providing per packet
-latency distribution for latency streams sent in parallel to the main
-load packet streams. Packet latency is measured using following
-methodology:
+TRex Traffic Generator (TG) is used for measuring one-way latency in
+2-Node and 3-Node physical testbed topologies. TRex integrates `High
+Dynamic Range Histogram (HDRH) <http://hdrhistogram.org/>`_
+functionality and reports per packet latency distribution for latency
+streams sent in parallel to the main load packet streams.
-- Latency tests are performed at following packet load levels:
+Following methodology is used:
+
+- Only NDRPDR test type measures latency and only after NDR and PDR
+ values are determined. Other test types do not involve latency
+ streams.
+- Latency is measured at different background load packet rates:
- No-Load: latency streams only.
- Low-Load: at 10% PDR.
- Mid-Load: at 50% PDR.
- High-Load: at 90% PDR.
- - NDR-Load: at 100% NDR.
- - PDR-Load: at 100% PDR.
- Latency is measured for all tested packet sizes except IMIX due to
- TG restriction.
+ TRex TG restriction.
- TG sends dedicated latency streams, one per direction, each at the
rate of 9 kpps at the prescribed packet size; these are sent in
addition to the main load streams.
- TG reports Min/Avg/Max and HDRH latency values distribution per stream
- direction, hence two sets of latency values are reported per test
- case.
-- Reported latency values are aggregate across tested topology.
-- +/- 1 usec is the measurement accuracy advertised by TRex TG for the
- setup used.
-- TG setup introduces an always-on Tx/Rx interface latency of about 2
- * 2 usec per direction induced by TRex SW writing and reading packet
- timestamps on CPU cores.
+ direction, hence two sets of latency values are reported per test case
+ (marked as E-W and W-E).
+- +/- 1 usec is the measurement accuracy of TRex TG and the data in HDRH
+ latency values distribution is rounded to microseconds.
+- TRex TG introduces a (background) always-on Tx + Rx latency bias of 4
+ usec on average per direction resulting from TRex software writing and
+ reading packet timestamps on CPU cores. Quoted values are based on TG
+ back-to-back latency measurements.
+- Latency graphs are not smoothed, each latency value has its own
+ horizontal line across corresponding packet percentiles.
+- Percentiles are shown on X-axis using a logarithmic scale, so the
+ maximal latency value (ending at 100% percentile) would be in
+ infinity. The graphs are cut at 99.9999% (hover information still
+ lists 100%). \ No newline at end of file