RE: [PATCH] perf/x86: Fix overlap counter scheduling bug

Liang, Kan
2016-11-08T16:22:19Z

> >
> >
> > diff --git a/arch/x86/events/intel/uncore_snbep.c
> > b/arch/x86/events/intel/uncore_snbep.c
> > index 272427700d48..71bc348736bd 100644
> > --- a/arch/x86/events/intel/uncore_snbep.c
> > +++ b/arch/x86/events/intel/uncore_snbep.c
> > @@ -669,7 +669,7 @@ static struct event_constraint
> snbep_uncore_cbox_constraints[] = {
> > UNCORE_EVENT_CONSTRAINT(0x1c, 0xc),
> > UNCORE_EVENT_CONSTRAINT(0x1d, 0xc),
> > UNCORE_EVENT_CONSTRAINT(0x1e, 0xc),
> > - EVENT_CONSTRAINT_OVERLAP(0x1f, 0xe, 0xff),
> > + UNCORE_EVENT_CONSTRAINT(0x1f, 0xc); /* should be 0x0e but that
> gives
> > +scheduling pain */

I think the crash is caused by the overlap bit.
Why not just revert the previous patch?

If overlap bit is removed, the perf_sched_save_state will never be touched.
Why we have to reduce a counter?

Thanks,
Kan

> > UNCORE_EVENT_CONSTRAINT(0x21, 0x3),
> > UNCORE_EVENT_CONSTRAINT(0x23, 0x3),
> > UNCORE_EVENT_CONSTRAINT(0x31, 0x3),
> >