From: "Metzger, Markus T" <markus.t.metzger@intel.com>
To: "mingo@elte.hu" <mingo@elte.hu>
CC: "hpa@zytor.com" <hpa@zytor.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "a.p.zijlstra@chello.nl" <a.p.zijlstra@chello.nl>,
       "Metzger, Markus T" <markus.t.metzger@intel.com>,
       "tglx@linutronix.de" <tglx@linutronix.de>,
       "mingo@redhat.com" <mingo@redhat.com>,
       "linux-tip-commits@vger.kernel.org" 
	<linux-tip-commits@vger.kernel.org>
Date: Mon, 21 Sep 2009 08:25:29 +0100
Subject: RE: [tip:perfcounters/core] x86, perf_counter, bts: Optimize BTS
 overflow handling
Thread-Topic: [tip:perfcounters/core] x86, perf_counter, bts: Optimize BTS
 overflow handling
Thread-Index: Aco4lOCeKJBMUzbGRgOPO3+Cewv2vQB9oFmw
Message-ID: <928CFBE8E7CB0040959E56B4EA41A77EC69BA609@irsmsx504.ger.corp.intel.com>
References: <20090915130023.A16204@sedona.ch.intel.com>
 <tip-5622f295b53fb60dbf9bed3e2c89d182490a8b7f@git.kernel.org>
In-Reply-To: <tip-5622f295b53fb60dbf9bed3e2c89d182490a8b7f@git.kernel.org>
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>-----Original Message-----
>From: tip tree robot [mailto:bounces.tip@hpa.at.zytor.com] On Behalf Of tip-bot for Markus Metzger
>Sent: Friday, September 18, 2009 9:19 PM
>To: linux-tip-commits@vger.kernel.org
>Cc: linux-kernel@vger.kernel.org; hpa@zytor.com; mingo@redhat.com; a.p.zijlstra@chello.nl; Metzger,
>Markus T; tglx@linutronix.de; mingo@elte.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@intel.com>
>AuthorDate: Tue, 15 Sep 2009 13:00:23 +0200
>Committer:  Ingo Molnar <mingo@elte.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@intel.com>
>Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
>LKML-Reference: <20090915130023.A16204@sedona.ch.intel.com>
>Signed-off-by: Ingo Molnar <mingo@elte.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.

thanks and regards,
markus.

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