linux-kernel - Re: [PATCH] [15/58] i386: Rewrite sched

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Date:	Fri, 20 Jul 2007 15:07:56 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
CC:	Andi Kleen <ak@...e.de>, patches@...-64.org,
	linux-kernel@...r.kernel.org, Daniel Walker <dwalker@...sta.com>
Subject: Re: [PATCH] [15/58] i386: Rewrite sched_clock (cmpxchg8b)

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.
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