linux-kernel - Re: [PATCH]: Fix SMP-reordering race in mark_buffer

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Date:	Wed, 2 Apr 2008 14:35:25 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
cc:	viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH]: Fix SMP-reordering race in mark_buffer_dirty

On Wed, 2 Apr 2008, Linus Torvalds wrote:
> 
> Core 2 is the outlier in having a noticeably faster "mfence" than atomic 
> instructions

Side note: mfence is probably faster than 6 cycles on Core 2. I've seen it 
be basically zero-cost. Try adding a few memory ops around it - the timing 
will probably change. Core 2 has this odd behaviour that it sometimes does 
worse on the *really* trivial things that don't happen in real life.

			Linus
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