linux-kernel - Re: perf_events: proposed fix for broken intr throttling (repost)

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Message-ID: <CABPqkBQ_MFdi1gc7Tje=u0n+RLd1gzo1mHb9e6i20T8JPNrpwA@mail.gmail.com>
Date:	Wed, 4 Jan 2012 23:02:42 +0000
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, gleb@...hat.com,
	asharma@...com, vince@...ter.net, wcohen@...hat.com
Subject: Re: perf_events: proposed fix for broken intr throttling (repost)

On Wed, Jan 4, 2012 at 10:49 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, 2012-01-04 at 21:33 +0000, Stephane Eranian wrote:
>> > I don't think it needs that, I do dislike the unconditional iterate all
>> > events thing though. Maybe we can set some per-cpu state indicating
>> > someone got throttled (rare under normal operation -- you'd hope) and
>> > only iterate to unthrottle when we find this set.
>> >
>> Could try that too.
>>
>> > I think the event scheduling resulting from migration will already
>> > re-enable the event, avoiding the loss of unthrottle due to that..
>> > although it would be good to verify that.
>> >
>> Yes, you're not dead forever, but still it is not acceptable as is.
>
> Oh for sure, I didn't mean it like that. What I was getting at is a
> counter getting throttled on one cpu, setting the per-cpu variable,
> getting migrated and not getting unthrottled due to now living on
> another cpu which doesn't have the per-cpu thing set.
>
Yes, that is true.
I think that throttled counter needs to live in ctx and not per-cpu.
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