linux-kernel - Re: [tip:perf/urgent] perf, x86: Complain louder about BIOSen corrupting CPU/PMU state and continue

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Message-ID: <20110325192303.GB22960@elte.hu>
Date:	Fri, 25 Mar 2011 20:23:03 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>, mingo@...hat.com,
	hpa@...or.com, acme@...hat.com, linux-kernel@...r.kernel.org,
	eric.dumazet@...il.com, efault@....de, fweisbec@...il.com,
	rostedt@...dmis.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/urgent] perf, x86: Complain louder about BIOSen
 corrupting CPU/PMU state and continue

* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> > This might also be something we do want to give a kernel command line
> > option for. As in "bios=allow-annoying-pmu-thing" or whatever.
> 
> I had such a patch, Ingo argued against it and we decided not to do it,
> but we could still.

Basically for many kernel releases we ignored the BIOS corrupting the PMU - so 
one could fairly argue that this patch fixes a perf functionality regression 
for Eric. We'll still warn in the syslog about the BIOS so there's an 
indication that something is going on.

Linus, which variant is the most efficient one in your opinion? I'm leaning 
slightly in favor of this patch in perf/urgent: it restores Eric's system to 
the before-BIOS-corruption-detection state, but also warns about the BIOS 
craziness.

	Ingo
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