linux-kernel - Re: WARNING: at arch/x86/kernel/cpu/perf

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Date:	Mon, 06 Feb 2012 16:02:48 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>
Subject: Re: WARNING: at arch/x86/kernel/cpu/perf_event.c:989

On Mon, 2012-02-06 at 15:32 +0100, Stephane Eranian wrote:
> I am wondering why we stop and restart the code in perf_adjust_period()
> when it's called from __perf_event_overflow(). Isn't it supposed to be stopped
> already by the model specific interrupt handler. Looks like we do stop/start,
> just to get the reload aspect of start. Is that right? 

Yes it is in order to deal with the case where an excessively long
period is programmed and we want to force load the new period without
having to wait for the old one to complete.

I hit that case several times with the adaptive code and events that
have very uneven rates.

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