linux-kernel - Re: [PATCH] i386-pda UP optimization

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Message-ID: <20061115172003.GA20403@elte.hu>
Date:	Wed, 15 Nov 2006 18:20:03 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <ak@...e.de>
Cc:	Eric Dumazet <dada1@...mosbay.com>, akpm@...l.org,
	Arjan van de Ven <arjan@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i386-pda UP optimization


* Andi Kleen <ak@...e.de> wrote:

> On Wednesday 15 November 2006 12:27, Eric Dumazet wrote:
> > Seeing %gs prefixes used now by i386 port, I recalled seeing strange 
> > oprofile results on Opteron machines.
> > 
> > I really think %gs prefixes can be expensive in some (most ?) cases, 
> > even if the Intel/AMD docs say they are free.
> 
> They aren't free, just very cheap.

Eric's test shows a 5% slowdown. That's far from cheap.

	Ingo
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