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

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Date:   Tue, 8 Nov 2016 16:22:13 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Andi Kleen <andi@...stfloor.org>,
        Peter Zijlstra <peterz@...radead.org>
CC:     Jiri Olsa <jolsa@...nel.org>, Vince Weaver <vince@...ter.net>,
        "Robert Richter" <rric@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: RE: [PATCH] perf/x86: Fix overlap counter scheduling bug



> >
> >
> > 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),
> >