2 title: "Packet Latency"
8 TRex Traffic Generator (TG) is used for measuring one-way latency in
9 2-Node and 3-Node physical testbed topologies. TRex integrates
10 [High Dynamic Range Histogram (HDRH)](http://hdrhistogram.org/)
11 functionality and reports per packet latency distribution for latency
12 streams sent in parallel to the main load packet streams.
14 Following methodology is used:
16 - Only NDRPDR test type measures latency and only after NDR and PDR
17 values are determined. Other test types do not involve latency
19 - Latency is measured at different background load packet rates:
21 - No-Load: latency streams only.
22 - Low-Load: at 10% PDR.
23 - Mid-Load: at 50% PDR.
24 - High-Load: at 90% PDR.
26 - Latency is measured for all tested packet sizes except IMIX due to
28 - TG sends dedicated latency streams, one per direction, each at the
29 rate of 9 kpps at the prescribed packet size; these are sent in
30 addition to the main load streams.
31 - TG reports Min/Avg/Max and HDRH latency values distribution per stream
32 direction, hence two sets of latency values are reported per test case
33 (marked as E-W and W-E).
34 - +/- 1 usec is the measurement accuracy of TRex TG and the data in HDRH
35 latency values distribution is rounded to microseconds.
36 - TRex TG introduces a (background) always-on Tx + Rx latency bias of 4
37 usec on average per direction resulting from TRex software writing and
38 reading packet timestamps on CPU cores. Quoted values are based on TG
39 back-to-back latency measurements.
40 - Latency graphs are not smoothed, each latency value has its own
41 horizontal line across corresponding packet percentiles.
42 - Percentiles are shown on X-axis using a logarithmic scale, so the
43 maximal latency value (ending at 100% percentile) would be in
44 infinity. The graphs are cut at 99.9999% (hover information still