linux-kernel - Re: [patch 4/7] Immediate Values

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Message-ID: <46F15ED4.40002@zytor.com>
Date:	Wed, 19 Sep 2007 10:39:32 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@....de>, Chuck Ebbert <cebbert@...hat.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [patch 4/7] Immediate Values - i386 Optimization

Jeremy Fitzhardinge wrote:
> 
> Cross-cache-line, sure.  But what about just not sizeof aligned?  If its
> enough to avoid cross-cache-line, then that's simpler.
> 

Not really.  It pretty much comes down to the same problem.

> Which is something I was going to comment on: Mathieu, you try to align
> the constant itself, but you don't prevent the instruction overall from
> crossing a cache line.  Given how delicate all this stuff is, it seems
> like a good idea to do that.

Given how delicate all his stuff is, it would be interesting to know the
magnitude of the expected payoff, which I personally don't remember seeing.

	-hpa

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