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

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Message-ID: <928CFBE8E7CB0040959E56B4EA41A77EC1CB7775@irsmsx504.ger.corp.intel.com>
Date:	Tue, 18 Aug 2009 14:20:30 +0100
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	"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: Peter Zijlstra [mailto:peterz@...radead.org]
>Sent: Tuesday, August 18, 2009 3:00 PM
>To: Metzger, Markus T
>Cc: Ingo Molnar; 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
>
>On Tue, 2009-08-18 at 14:59 +0200, Peter Zijlstra wrote:
>> On Tue, 2009-08-18 at 13:49 +0100, Metzger, Markus T wrote:
>> > Hi Ingo, Peter,
>> >
>> > Did you say that branch tracing is working for you?
>> >
>> > On my system, the kernel hangs.
>> >
>> > Could it be that it simply takes too long to copy the trace? When I set the number
>> > of samples to 10, everything seems to work OK. When I increase that number to 1000,
>> > the kernel is getting very slow and eventually hangs.
>> >
>> > I get a message "hrtimer: interrupt too slow", and I get a soft lockup bug. The rest
>> > of the message log seems pretty garbled.
>
>How many NMI/s is this generating anyway?

One every 800 or so branches in the current configuration - which results in 800 plus
a few perf_counter_output() calls per interrupt.

regards,
markus.
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