linux-kernel - Re: [tip:perfcounters/core] x86, perf_counter, bts: Optimize BTS overflow handling

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Message-ID: <20090921073232.GC24467@elte.hu>
Date:	Mon, 21 Sep 2009 09:32:32 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Metzger, Markus T" <markus.t.metzger@...el.com>
Cc:	"hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:perfcounters/core] x86, perf_counter, bts: Optimize BTS
	overflow handling


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

> >-----Original Message-----
> >From: tip tree robot [mailto:bounces.tip@....at.zytor.com] On Behalf Of tip-bot for Markus Metzger
> >Sent: Friday, September 18, 2009 9:19 PM
> >To: linux-tip-commits@...r.kernel.org
> >Cc: linux-kernel@...r.kernel.org; hpa@...or.com; mingo@...hat.com; a.p.zijlstra@...llo.nl; Metzger,
> >Markus T; tglx@...utronix.de; mingo@...e.hu
> >Subject: [tip:perfcounters/core] x86, perf_counter, bts: Optimize BTS overflow handling
> >
> >Commit-ID:  5622f295b53fb60dbf9bed3e2c89d182490a8b7f
> >Gitweb:     http://git.kernel.org/tip/5622f295b53fb60dbf9bed3e2c89d182490a8b7f
> >Author:     Markus Metzger <markus.t.metzger@...el.com>
> >AuthorDate: Tue, 15 Sep 2009 13:00:23 +0200
> >Committer:  Ingo Molnar <mingo@...e.hu>
> >CommitDate: Fri, 18 Sep 2009 20:43:20 +0200
> >
> >x86, perf_counter, bts: Optimize BTS overflow handling
> >
> >Draining the BTS buffer on a buffer overflow interrupt takes too
> >long resulting in a kernel lockup when tracing the kernel.
> >
> >Restructure perf_counter sampling into sample creation and sample
> >output.
> >
> >Prepare a single reference sample for BTS sampling and update the
> >from and to address fields when draining the BTS buffer. Drain the
> >entire BTS buffer between a single perf_output_begin() /
> >perf_output_end() pair.
> >
> >Signed-off-by: Markus Metzger <markus.t.metzger@...el.com>
> >Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> >LKML-Reference: <20090915130023.A16204@...ona.ch.intel.com>
> >Signed-off-by: Ingo Molnar <mingo@...e.hu>
> 
> 
> Ingo,
> 
> This change should speed up BTS overflow handling enough to support
> branch tracing the kernel.
> Would you please drop 1653192f510bd8114b7b133d7289e6e5c3e95046
> that disabled kernel tracing to work around the issue.

Please send a proper patch that re-enables the (previously unreliable) 
aspect of BTS tracing, with a changelog that explains that the feature 
now works and with an indication that you've tested it.

	Ingo
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