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Date: Mon, 29 Mar 2010 15:20:57 +0100
Message-ID: <bd4cb8901003290720j3ab10830vf449e59c40c1e5c0@mail.gmail.com>
Subject: Re: [RFC,PATCH 2/2] perf, x86: Utilize the LBRs for machine/oops 
	debugging
From: Stephane Eranian <eranian@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@elte.hu, Linus Torvalds <torvalds@osdl.org>,
       linux-kernel@vger.kernel.org
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On Mon, Mar 29, 2010 at 3:13 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, 2010-03-29 at 13:47 +0100, Stephane Eranian wrote:
>> On Mon, Mar 29, 2010 at 1:20 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
>> > The LBRs are relatively cheap to keep enabled and provide some history
>> > to OOPSen, also some CPUs are reported to keep them over soft-reset,
>> > which allows us to use them to debug things like tripple faults.
>> >
>> > Therefore introduce a boot option: lbr_debug=on, which always enable
>> > the LBRs and will print the LBRs on CPU init and die().
>> >
>>
>> When this is enabled, it will prevent changing the LBR configuration to
>> record only selected branches. Unless you are willing to accept filtered
>> content in the kernel dump.
>
> Sure, but since we don't support that silly config reg anyway that's
> pretty much not an issue ;-)
>
I will provide a patch to make it available. This is needed for certain
measurements.