linux-kernel - RE: [patch] x86, perf_counter, bts: add bts to perf

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Date:	Fri, 7 Aug 2009 08:29:05 +0100
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	"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>
Subject: RE: [patch] x86, perf_counter, bts: add bts to perf_counter

>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@...e.hu]
>Sent: Tuesday, August 04, 2009 1:36 PM
>To: Peter Zijlstra
>Cc: Metzger, Markus T; tglx@...utronix.de; hpa@...or.com; markus.t.metzger@...il.com; linux-
>kernel@...r.kernel.org
>Subject: Re: [patch] x86, perf_counter, bts: add bts to perf_counter
>
>
>* Ingo Molnar <mingo@...e.hu> wrote:
>
>> > Over all looks very nice, some comments below (could be
>> > addressed in a delta patch).
>>
>> ok - thanks guys - i'll test this some and push it out into the
>> perfcounters tree. Will apply the delta patch too once it's done.
>
>the kernel hard-locks if i try to use it:
>
> titan:~/tip/tools/perf> perf record -f -e branches -c 1 ~/hackbench 1
>
>with the attached 64-bit (def-)config, on a Core2 test-box, latest
>-tip.

Ingo, thanks for reporting the issue!

I forgot to set the BTINT bit.

I now also set pending_kill = POLL_IN as perf_counter_overflow() would do when draining BTS.

I incorporated Peter's review comments, except that I would not enforce sample_period == 1
when branch tracing is requested. There might be users who want to sample the IP every 100.000'th
branch for profiling reasons.

regards,
markus.

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