X-Git-Url: https://gerrit.fd.io/r/gitweb?p=csit.git;a=blobdiff_plain;f=docs%2Freport%2Fintroduction%2Fmethodology_packet_latency.rst;fp=docs%2Freport%2Fintroduction%2Fmethodology_packet_latency.rst;h=b8df6605394bb38daa1eeb79d628ce5fcfa8be79;hp=411fe3d6fe5ad38f346ffbd914c90e9107160ace;hb=afb2897f174374695eeffdf0675b0418f5dc55e4;hpb=1ced14ce1707a27679002db43c4761853ddb83de

diff --git a/docs/report/introduction/methodology_packet_latency.rst b/docs/report/introduction/methodology_packet_latency.rst
index 411fe3d6fe..b8df660539 100644
--- a/docs/report/introduction/methodology_packet_latency.rst
+++ b/docs/report/introduction/methodology_packet_latency.rst
@@ -1,23 +1,33 @@
 Packet Latency
 --------------
 
-TRex Traffic Generator (TG) is used for measuring latency of VPP DUTs.
-Reported latency values are measured using following methodology:
+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:
 
-- Latency tests are performed at 100% of discovered NDR and PDR rates
-  for each throughput test and packet size (except IMIX).
+- Latency tests are performed at following packet load levels:
+
+  - 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.
 - 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.
+- 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.
\ No newline at end of file