linux-kernel - Re: [PATCH tip:x86/mm 1/3] x86: A fast way to check capabilities of the current cpu

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Message-ID: <20110330160756.GL17523@htj.dyndns.org>
Date:	Wed, 30 Mar 2011 18:07:56 +0200
From:	Tejun Heo <tj@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Christoph Lameter <cl@...ux.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: [PATCH tip:x86/mm 1/3] x86: A fast way to check capabilities
 of the current cpu

Hello,

On Wed, Mar 30, 2011 at 08:58:23AM -0700, H. Peter Anvin wrote:
> >> Add this_cpu_has() which determines if the current cpu has a certain
> >> ability using a segment prefix and a bit test operation.
> > 
> > 
> > Hmm: if the CPU capability is really tested in a performance critical
> > path, wouldn't it even be better to just use static_branch() now? 
> > 
> 
> We have static_cpu_has() for this specific purpose (it actually predates
> static_branch()).

These patches have performance benefits but I don't think it would be
noticeable.  I think it's more of code cleanup.

Thanks.

-- 
tejun
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