CSIT-1420: Split methodology section to more files

[csit.git] / docs / report / introduction / methodology_packet_latency.rst

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+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 due to three
+  node topology used for all performance tests; 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.