Packet Latency

TRex Traffic Generator (TG) is used for measuring latency of VPP DUTs. Reported latency values are measured using following methodology:

• Latency tests are performed at 100% of discovered NDR and PDR rates for each throughput test and packet size (except IMIX).
• 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 latency values per stream direction, hence two sets of latency values are reported per test case; future release of TRex is expected to report latency percentiles.
• Reported latency values are aggregate across two SUTs if the three node topology is used for given performance test; for per SUT latency, reported value should be divided by two.
• 1usec is the measurement accuracy advertised by TRex TG for the setup used in FD.io labs used by CSIT project.
• TRex setup introduces an always-on error of about 2*2usec per latency flow additonal Tx/Rx interface latency induced by TRex SW writing and reading packet timestamps on CPU cores without HW acceleration on NICs closer to the interface line.