The “show run” stats use rdtsc instructions, vs. “show pmc” which uses rdpmc instructions with a specific counter selected.
Perhaps Damjan or one of our colleagues from Intel can explain the difference. D. From: vpp-dev@lists.fd.io <vpp-dev@lists.fd.io> On Behalf Of Kingwel Xie Sent: Tuesday, December 11, 2018 5:18 AM To: Dave Barach (dbarach) <dbar...@cisco.com>; vpp-dev <vpp-dev@lists.fd.io> Subject: [vpp-dev] perfmon plugin Hi Dave, I’m looking at the perfmon plugin. It is a fantastic tool tuning node performance, extremely helpful. Thanks for the great contribution. Here I got a question about ‘cpu-cycles’ event. It shows very different results if comparing with clocks of ‘show run’. Around 20% slower. I checked the code but didn’t find anything wrong. Also I tried ‘instructions’, it is normal. Please check below: Show run: ip4-input active 41843 10711808 0 3.32E+01 256 ppf-pdcp-encap active 41843 10711808 0 2.69E+01 256 Show pmc: t1-ip4-input instructions-per-clo 1609959354 510202112 3.16E+00 instructions 1609959354 15727872 1.02E+02 cpu-cycles 510202112 12838400 3.97E+01 t1-ppf-pdcp-encap instructions-per-clo 1229445506 415212396 2.96E+00 instructions 1229445506 15727872 7.82E+01 cpu-cycles 415212396 12838400 3.23E+01 So the question is : will the turning on perf event impact system performance? If so, why ‘instruction’ event does not? You might notice that packet count recorded by ‘instructions’ is very different from that by ‘cpu-cycles’, even they are both measured under the same circumstance – running for 3s. Regards, Kingwel
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