Messages in this thread | | | From | Andy Lutomirski <> | Date | Thu, 23 Jul 2015 08:52:50 -0700 | Subject | Re: [PATCH RFC V2 1/1] x86, perf: Add a freq pmu driver |
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On Thu, Jul 23, 2015 at 8:44 AM, Stephane Eranian <eranian@google.com> wrote: > I understand the value of the tsc and smi events. It is not > clear to me what aperf/mperf buys you over cycles and ref-cycles: > > $ perf stat -a -e msr/aperf/,msr/mperf/,cycles,ref-cycles -C 1 -I 1000 sleep 10 > # time counts unit events > 2.000361718 14,826,353 msr/aperf/ > 2.000361718 11,865,170 msr/mperf/ > 2.000361718 17,170,101 cycles > 2.000361718 13,629,675 ref-cycles > > Only the ratio aperf/mperf is defined, here 1.25 and the ratio > cycles/ref-cycles is 1.25 as well. So what is a situation where > aperf/mperf provides better info than cycles/ref-cycles? > The SDM also says aperf/mperf only defined when running in C0 mode.
They're free-running and always on, which means that you can never fail to schedule them.
--Andy
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