Messages in this thread | | | From | "Liang, Kan" <> | Subject | RE: [PATCH V2 03/13] perf/x86: output sampling overhead | Date | Tue, 6 Dec 2016 15:47:40 +0000 |
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> On Tue, Dec 06, 2016 at 03:02:20PM +0000, Liang, Kan wrote: > > > > > > > On Fri, Dec 02, 2016 at 04:19:11PM -0500, kan.liang@intel.com wrote: > > > > From: Kan Liang <kan.liang@intel.com> > > > > > > > > On x86, NMI handler is the most important part which brings > > > > overhead for sampling. Adding a pmu specific overhead type > > > > PERF_PMU_SAMPLE_OVERHEAD for it. > > > > > > > > For other architectures which may don't have NMI, the overhead > > > > type can be reused. > > > > > > > > Signed-off-by: Kan Liang <kan.liang@intel.com> > > > > --- > > > > arch/x86/events/core.c | 17 ++++++++++++++++- > > > > arch/x86/events/perf_event.h | 2 ++ > > > > include/uapi/linux/perf_event.h | 1 + > > > > 3 files changed, 19 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index > > > > 9d4bf3a..de40f96 100644 > > > > --- a/arch/x86/events/core.c > > > > +++ b/arch/x86/events/core.c > > > > @@ -1397,6 +1397,9 @@ static void x86_pmu_del(struct perf_event > > > > *event, int flags) > > > > > > > > perf_event_update_userpage(event); > > > > > > > > + if ((flags & PERF_EF_LOG) && cpuc->nmi_overhead.nr) > > > > + perf_log_overhead(event, PERF_PMU_SAMPLE_OVERHEAD, > > > > +&cpuc->nmi_overhead); > > > > + > > > > do_del: > > > > if (x86_pmu.del) { > > > > /* > > > > > > That's not at all mentioned in the changelog, and it clearly isn't > > > nmi_overhead. > > > > Here it only records the overhead, not calculate. > > It doesn't record anything, it generates the output. And it doesn't explain > why that needs to be in pmu::del(), in general that's a horrible thing to do.
Yes, it only generate/log the output. Sorry for the confused wording.
The NMI overhead is pmu specific overhead. So the NMI overhead output should be generated in pmu code. I assume that the pmu:del is the last called pmu function when perf finish. Is it a good place for logging?
Thanks, Kan
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