linux-kernel - Re: [PATCH RFC] x86: avoid atomic operation in test_and_set_bit

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Message-ID: <20110325105055.GA7281@aftab>
Date:	Fri, 25 Mar 2011 11:50:55 +0100
From:	Borislav Petkov <bp@...64.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jack Steiner <steiner@....com>,
	Jan Beulich <JBeulich@...ell.com>,
	Borislav Petkov <bp@...64.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...nel.dk>,
	"x86@...nel.org" <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>, "tee@....com" <tee@....com>,
	Nikanth Karthikesan <knikanth@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Robert Richter <robert.richter@....com>
Subject: Re: [PATCH RFC] x86: avoid atomic operation in
 test_and_set_bit_lock if possible

On Fri, Mar 25, 2011 at 05:59:31AM -0400, Ingo Molnar wrote:
> > [...] but you probably need to make a full pass to make sure we dont have a 
> > MSR failure -this should return false in this case.
>
> Wanted to keep this patch simple - we are not really hitting MSR
> failure cases in practice, and by getting the message the user is at
> least warned that *something* is amiss.

AFAIR, Robert was telling me couple of months ago about some braindead
BIOSes doing power management by using at least one perf counter. A
radical approach like that might interfere with that BIOS since it will
try to reprogram the counter continuously and f*ck up OS PMU use.

Anyway, adding Robert for clarification.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
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Registration: Dornach, Gemeinde Aschheim, Landkreis Muenchen
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