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-rw-r--r--docs/report/introduction/methodology_packet_latency.rst42
1 files changed, 26 insertions, 16 deletions
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