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

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Message-ID: <928CFBE8E7CB0040959E56B4EA41A77EC1CB77FF@irsmsx504.ger.corp.intel.com>
Date:	Tue, 18 Aug 2009 15:15:14 +0100
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
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

>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@...e.hu]
>Sent: Tuesday, August 18, 2009 4:00 PM
>To: Metzger, Markus T
>Cc: Peter Zijlstra; tglx@...utronix.de; hpa@...or.com; markus.t.metzger@...il.com; linux-
>kernel@...r.kernel.org; Paul Mackerras
>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.

So you do not think that taking too long in the ISR could cause this?

And is it working 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.

How would I test this?


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

The old BTS code used circular buffers.


regards,
markus.

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