On Thu, Apr 30, 2015 at 1:51 AM, Peter Zijlstra <pet...@infradead.org> wrote: > On Wed, Apr 29, 2015 at 06:17:05PM -0700, Andy Lutomirski wrote: >> >> > + /* no sampling */ >> >> > + if (event->hw.sample_period) >> >> > + return -EINVAL; >> >> >> >> You could have set pmu::capabilities = >> >> PERF_PMU_CAP_NO_INTERRUPT which would also have killed that dead. >> > >> > >> > That checks attr.sample_period. I'm a bit confused about the >> > relationship between event->hw and event->attr. Do I not need to >> > check hw.sample_period? > > event->attr is the perf_event_attr used to instantiate the event. > event->hw is the hardware/working state of the event. > > You'll notice that attr::sample_period is part of a union and when > !attr::freq will be used as the actual hw::sample_period. However when > attr::freq we'll compute hw::sample_period based on actual event rates > such that we'll approx attr::sample_freq. > > Setting pmu::capabilities = PERF_PMU_CAP_NO_INTERRUPT would be the best > solution here. > >> > Before I submit v2, do you think this is actually worth doing? I can >> > see it being useful for answering questions like "did this workload >> > end up running at full speed". >> > >> >> To clarify, this is partially redundant with "cpu-cycles" and >> "ref-cycles". That being said, these are simpler, actually documented >> as being appropriate for measuring cpu performance states, and don't >> have any scheduling constraints. > > On the whole useful question; I dunno. It seems like something worth > providing for the reasons you state. But I don't really get around to > doing much userspace these days so I might not be the best to answer > this. > > Also, you could extend this with IA32_PPERF (Skylake and later, see > SDM-201501 book 3 section 14.4.5.1).
Interesting. I can't test it for obvious reasons, and the enumeration is not really straightforward, since it's non-architectural. If I send the patch, can you test? Should the PMU still be called aperfmperf? > >> Also, is perf stat able to count while idle? perf stat -a -e >> cpu-cycles sleep 1 reports very small numbers. > > Yes, perf stat -a (iow cpu events) should count while idle, note however > that not all events count during halt, so its very much event dependent. I see. MPERF, etc only count in C0. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
