> > On Mon, May 22, 2017 at 12:23 PM, Peter Zijlstra <pet...@infradead.org> > wrote: > > On Mon, May 22, 2017 at 04:55:47PM +0000, Liang, Kan wrote: > >> > >> > >> > On Fri, May 19, 2017 at 10:06:21AM -0700, kan.li...@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. > > Yes, it must be. Because you can reconstruct the total number of occurrences > of the event by adding all the periods recorded in each sample. So the period > in each sample must reflect user event and not kernel event.
Peter and Stephane, you are right. After adjusting the period, I can only make sure the number of samples for the bus_cycles event is the same as that for ref cycles event. I still need to adjust the number of occurrences of the event accordingly, to make it accurate. I will change it in next version. Thanks, Kan
