Date: Tue, 26 May 2015 15:22:21 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Stephane Eranian <eranian@google.com>
Cc: Ingo Molnar <mingo@kernel.org>, Vince Weaver <vincent.weaver@maine.edu>,
        Jiri Olsa <jolsa@redhat.com>, "Liang, Kan" <kan.liang@intel.com>,
        LKML <linux-kernel@vger.kernel.org>, Andrew Hunter <ahh@google.com>,
        Maria Dimakopoulou <maria.n.dimakopoulou@gmail.com>
Subject: Re: [PATCH v2 01/11] perf,x86: Fix event/group validation
Message-ID: <20150526132221.GP3644@twins.programming.kicks-ass.net>
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On Tue, May 26, 2015 at 05:25:59AM -0700, Stephane Eranian wrote:
> > IIRC the problem was that the copy from c2 into c1:
> >
> >         if (c1 && (c1->flags & PERF_X86_EVENT_DYNAMIC)) {
> >                 bitmap_copy(c1->idxmsk, c2->idxmsk, X86_PMC_IDX_MAX);
> >                 c1->weight = c2->weight;
> >                 c2 = c1;
> >         }
> >
> > is incomplete. For instance, flags is not copied, and some code down the
> > line might check that and get wrong flags.
> >
> Ok, now I remember this code. It has to do with incremental scheduling.
> Suppose E1, E2, E3 events where E1 is exclusive. The first call is
> for scheduling E1. It gets to get_event_constraint() which "allocates" a
> dynamic constraint. The second call  tries to schedule E1, E2. But the
> second time for E1, you already have the dynamic constraint allocated, so
> this code is reusing the constraint storage and just updates the bitmask
> and weight.
> 
> Now, that the storage is not actually dynamic (kmalloc'd), but taken from a
> fixed size array in cpuc, I believe we can simplify this and "re-allocate"
> the constraint for each incremental call to intel_get_event_constraints().
> Do you agree?

That would probably work, the whole incremental thing seems superfluous
to me.
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