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Date: Fri, 20 Jul 2007 15:07:56 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Mathieu Desnoyers <compudj@krystal.dyndns.org>
CC: Andi Kleen <ak@suse.de>, patches@x86-64.org, linux-kernel@vger.kernel.org,
       Daniel Walker <dwalker@mvista.com>
Subject: Re: [PATCH] [15/58] i386: Rewrite sched_clock (cmpxchg8b)
References: <200707191154.642492000@suse.de> <20070719095459.E60AD14E11@wotan.suse.de> <1184863904.6458.17.camel@dhcp193.mvista.com> <20070720031105.GA8237@Krystal> <20070720034757.GA9093@Krystal> <20070720041839.GA11217@Krystal>
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Mathieu Desnoyers wrote:

> I tried it with and without the LOCK prefix on my Pentium 4.
> 
> Locked cmpxchg8b : 90 cycles
> Non locked cmpxchg8b: 30 cycles
> sti: 166 cycles
> cli: 159 cycles
> 
> So, hrm, even if we use the locked version, it is still much faster than
> the sti/cli. I am thoughtful about the comment in asm-i386/system.h:

Curious: what does it look like if the memory is not in cache? I
found that cmpxchg is relatively slower than other rmw instructions
in that case.

-- 
SUSE Labs, Novell Inc.