linux-kernel - Re: [PATCH 1/2] x86: fix keeping track of AMD C1E

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Date:	Fri, 16 Jul 2010 15:28:33 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <borislav.petkov@....com>
CC:	Michal Schmidt <mschmidt@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Herrmann3, Andreas" <Andreas.Herrmann3@....com>,
	Shaohua Li <shaohua.li@...el.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 1/2] x86: fix keeping track of AMD C1E

On 07/16/2010 09:25 AM, Borislav Petkov wrote:
> 
> I don't see the need for two things denoting C1E for the very simple
> reason: when C1E gets enabled on a machine, one of the bits gets set in
> the MSR on each core simultaneously. So if one core sees one of the bits
> set, all the remaining cores are seeing them too. The first core that
> sees one of the bits in the MSR, sets c1e_detected.
> 
> So next time any core does cpu_idle() => c1e_idle(), it switches to
> timer broadcast on it since it might go into C1E if all the others
> follow.
> 
> Frankly, I can't think of a case where we'd need to two things - I
> could be missing something. But this workaround is a couple of years
> old, maybe Thomas might give us more insight into whether there's a
> particular reason for the cpuid flag and the c1e_detected variable.
> Thomas?
> 

I'm not saying there should be two things (and that's clearly wrong no
matter what), but rather it's not clear to me that the one thing should
be a variable.

	-hpa
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