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Date: Thu, 7 Apr 2011 18:42:45 +0200
From: Andi Kleen <andi@firstfloor.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@mit.edu>, x86@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        Andi Kleen <andi@firstfloor.org>, linux-kernel@vger.kernel.org
Subject: Re: [RFT/PATCH v2 2/6] x86-64: Optimize vread_tsc's barriers
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> But before that, I would check that the second lfence is needed AT
> ALL. I don't know whether we ever tried the "only barrier before"
> version, because quite frankly, if you call this thing in a loop, then

> a single barrier will still mean that there are barriers in between
> iterations. So...

The testers will call it in a loop, but real users (e.g. using it for
a logging timestamp) may not.

I'm sure a single barrier would have fixed the testers, as you point out,
but the goal wasn't to only fix testers.

-Andi
-- 
ak@linux.intel.com -- Speaking for myself only.