+++ /dev/null
-.. _latency_methodology:
-
-Packet Latency
-^^^^^^^^^^^^^^
-
-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.
-
-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.
-
-- Latency is measured for all tested packet sizes except IMIX due to
- 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
- (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%).
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Code Review / csit.git / blobdiff