Date: Fri, 25 Mar 2011 11:50:55 +0100
From: Borislav Petkov <bp@amd64.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Eric Dumazet <eric.dumazet@gmail.com>, Andi Kleen <andi@firstfloor.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jack Steiner <steiner@sgi.com>, Jan Beulich <JBeulich@novell.com>,
        Borislav Petkov <bp@amd64.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Nick Piggin <npiggin@kernel.dk>, "x86@kernel.org" <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, "tee@sgi.com" <tee@sgi.com>,
        Nikanth Karthikesan <knikanth@suse.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Robert Richter <robert.richter@amd.com>
Subject: Re: [PATCH RFC] x86: avoid atomic operation in
 test_and_set_bit_lock if possible
Message-ID: <20110325105055.GA7281@aftab>
References: <1300999682.2714.23.camel@edumazet-laptop>
 <20110324205422.GB2393@elte.hu>
 <1301000557.2714.33.camel@edumazet-laptop>
 <m2oc50kxg0.fsf@firstfloor.org>
 <AANLkTimib3TqemF9L=VNkcXT3uFam1gYmVtuA3wrAv1j@mail.gmail.com>
 <20110324235654.GM21838@one.firstfloor.org>
 <1301032040.2714.569.camel@edumazet-laptop>
 <20110325093228.GB13640@elte.hu>
 <1301046298.3268.4.camel@edumazet-laptop>
 <20110325095931.GA31903@elte.hu>
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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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