linux-kernel - Re: [patch 02/12] Immediate Values

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Message-ID: <20090928223735.74267e3e@infradead.org>
Date:	Mon, 28 Sep 2009 22:37:35 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Jason Baron <jbaron@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Adrian Bunk <bunk@...sta.de>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [patch 02/12] Immediate Values - Architecture Independent Code

On Mon, 28 Sep 2009 21:54:45 +0200
Andi Kleen <andi@...stfloor.org> wrote:

> > btw just to add to this:
> > caches are unified code/data after L1 in general... it then does not
> > matter much if you encode the "almost constant" in the codestream or
> > slightly farther away, in both cases it takes up cache space.
> 
> It does take up cache space, but when it's embedded in the instruction
> stream the CPU has it usually already prefetched (CPUs are very good
> at prefetching instructions). That's often not the case
> with arbitary data accesses like this.

this makes me wonder what happens when a variable is used in multiple
places... that makes the icache overhead multiply right?


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
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