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    SubjectRe: [PATCH 1/2] perf/x86/intel: enable CPU ref_cycles for GP counter
    On Mon, May 22, 2017 at 04:55:47PM +0000, Liang, Kan wrote:
    >
    >
    > > On Fri, May 19, 2017 at 10:06:21AM -0700, kan.liang@intel.com wrote:
    > > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index
    > > > 580b60f..e8b2326 100644
    > > > --- a/arch/x86/events/core.c
    > > > +++ b/arch/x86/events/core.c
    > > > @@ -101,6 +101,10 @@ u64 x86_perf_event_update(struct perf_event
    > > *event)
    > > > delta = (new_raw_count << shift) - (prev_raw_count << shift);
    > > > delta >>= shift;
    > > >
    > > > + /* Correct the count number if applying ref_cycles replacement */
    > > > + if (!is_sampling_event(event) &&
    > > > + (hwc->flags & PERF_X86_EVENT_REF_CYCLES_REP))
    > > > + delta *= x86_pmu.ref_cycles_factor;
    > >
    > > That condition seems wrong, why only correct for !sampling events?
    > >
    >
    > For sampling, it's either fixed freq mode or fixed period mode.
    > - In the fixed freq mode, we should do nothing, because the adaptive
    > frequency algorithm will handle it.
    > - In the fixed period mode, we have already adjusted the period in
    > ref_cycles_rep().
    > Therefore, we should only handle !sampling events here.

    How so? For sampling events the actual event count should also be
    accurate.

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