Got it. Thanks! My CPU is “Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz”. As I can see, the CPU is kind of running slower when ‘cpu-cycles’ event is enabled, while it is normal with ‘instructions’ event is enabled.
You can see the difference shown below. Texts in red are vector counts for the two events, in 3s. I got this by running ‘set pmc instructions-per-clock’. Therefore, it is hard to believe the ‘rdpmc’ cause the big difference – 80%. t1-ip4-input instructions-per-clo 1609959354 510202112 3.16E+00 instructions 1609959354 15727872 1.02E+02 cpu-cycles 510202112 12838400 3.97E+01 Hope somebody point out the root cause. Regards, Kingwel From: vpp-dev@lists.fd.io <vpp-dev@lists.fd.io> On Behalf Of Damjan Marion via Lists.Fd.Io Sent: Wednesday, December 12, 2018 12:30 AM To: Dave Barach <dbar...@cisco.com> Cc: vpp-dev@lists.fd.io Subject: Re: [vpp-dev] perfmon plugin rdtsc instruction reads timestamp counter which ticks on the constant nominal frequency which means that it will count ticks equally even when CPU is in deep sleep or when CPU is in turbo burst mode. That gives very precise time measurement (i.e. on 2.5GHz CPU tick will always be 0.4ns) but it is not appropriate for counting real cpu clock cycles. -- Damjan On 11 Dec 2018, at 06:02, Dave Barach via Lists.Fd.Io <dbarach=cisco....@lists.fd.io<mailto:dbarach=cisco....@lists.fd.io>> wrote: 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<mailto:vpp-dev@lists.fd.io> <vpp-dev@lists.fd.io<mailto: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<mailto:dbar...@cisco.com>>; vpp-dev <vpp-dev@lists.fd.io<mailto: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 -=-=-=-=-=-=-=-=-=-=-=- Links: You receive all messages sent to this group. View/Reply Online (#11562): https://lists.fd.io/g/vpp-dev/message/11562 Mute This Topic: https://lists.fd.io/mt/28717911/675642 Group Owner: vpp-dev+ow...@lists.fd.io<mailto:vpp-dev+ow...@lists.fd.io> Unsubscribe: https://lists.fd.io/g/vpp-dev/unsub [dmar...@me.com<mailto:dmar...@me.com>] -=-=-=-=-=-=-=-=-=-=-=-
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