linux-kernel - Re: [RFC,PATCH 2/2] perf, x86: Utilize the LBRs for machine/oops debugging

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Message-ID: <1269872024.12097.337.camel@laptop>
Date:	Mon, 29 Mar 2010 16:13:44 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	mingo@...e.hu, Linus Torvalds <torvalds@...l.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC,PATCH 2/2] perf, x86: Utilize the LBRs for machine/oops 
 debugging

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@...llo.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 ;-)

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