linux-kernel - Re: [PATCH] perf_counter: Fix a race on perf_counter

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Date:	Tue, 18 Aug 2009 16:00:22 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Metzger, Markus T" <markus.t.metzger@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"markus.t.metzger@...il.com" <markus.t.metzger@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH] perf_counter: Fix a race on perf_counter_ctx


* Metzger, Markus T <markus.t.metzger@...el.com> wrote:

> Well, that would push out the limit a bit, but it would still be 
> quite fragile.
> 
> Currently, I'm not sure that this (i.e. that the interrupt 
> handling takes too long) is the underlying problem of the hangs 
> that I'm seeing.

I havent seen a plausible theory yet about why an actual lockup 
would happen on your box.

Does the timer IRQ perhaps slow down to such a degree that it can 
never make progress and gets re-triggered again and again? We saw 
such things with the function tracer.

Did the sampling of kernel-mode tasks ever work with the old BTS 
code?

	Ingo
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