linux-kernel - Re: [PATCH] perf_events: fix event scheduling issues introduced by transactional API (take 2)

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Message-ID: <AANLkTiluTGxqQN4OU9ETAjb1SUD4ry-pewAtuzE1r54U@mail.gmail.com>
Date:	Tue, 25 May 2010 18:20:15 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	eranian@...il.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	paulus@...ba.org, davem@...emloft.net, fweisbec@...il.com,
	acme@...radead.org, ming.m.lin@...el.com,
	perfmon2-devel@...ts.sf.net
Subject: Re: [PATCH] perf_events: fix event scheduling issues introduced by 
	transactional API (take 2)

On Tue, May 25, 2010 at 6:18 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2010-05-25 at 18:10 +0200, Stephane Eranian wrote:
>> > Index: linux-2.6/kernel/perf_event.c
>> > ===================================================================
>> > --- linux-2.6.orig/kernel/perf_event.c
>> > +++ linux-2.6/kernel/perf_event.c
>> > @@ -668,15 +668,9 @@ group_sched_in(struct perf_event *group_
>> >                }
>> >        }
>> >
>> > -       if (!txn)
>> > +       if (!txn || !pmu->commit_txn(pmu))
>> >                return 0;
>> >
>> > -       ret = pmu->commit_txn(pmu);
>> > -       if (!ret) {
>> > -               pmu->cancel_txn(pmu);
>> > -               return 0;
>> > -       }
>> > -
>> >  group_error:
>> >        /*
>> >         * Groups can be scheduled in as one unit only, so undo any
>> >
>> Looks okay.
>>
>> I believe you can also drop the txn test in group_sched_in() after group_error:,
>> given you have the if !(txn) return 0.
>
> Can't we still get in the group_error: branch with either scenario?
>
You're right. We must keep it because of failure in the siblings' loop.
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