linux-kernel - Re: [PATCH 0/4] i386 - pte update optimizations

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Date:	Fri, 13 Apr 2007 08:00:46 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Zachary Amsden <zach@...are.com>
CC:	"H. Peter Anvin" <hpa@...or.com>, Andrew Morton <akpm@...l.org>,
	Andi Kleen <ak@....de>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Chris Wright <chrisw@...s-sol.org>,
	Hugh Dickins <hugh@...itas.com>,
	David Rientjes <rientjes@...gle.com>,
	Michel Lespinasse <walken@...are.com>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] i386 - pte update optimizations

Zachary Amsden a écrit :
> 
> Yes.  Even then, last time I clocked instructions, xchg was still slower 
> than read / write, although I could be misremembering.  And it's not 
> totally clear that they will always be in cached state, however, and for 
> SMP, we still want to drop the implicit lock in cases where the 
> processor might not know they are cached exclusive, but we know there 
> are no other racing users.  And there are plenty of old processors out 
> there to still make it worthwhile.
> 

Is there one processor that benefit from this patch then ?

I couldnt get a win on my test machines, maybe they are not old enough ;)

umask() doesnt need xchg() atomic semantic. If several threads are using 
umask() concurrently results are not guaranted anyway.

View attachment "umask.patch" of type "text/plain" (442 bytes)