linux-kernel - Re: [rfc][patch] store-free path walking

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Message-ID: <alpine.LFD.2.01.0910071349190.3432@localhost.localdomain>
Date:	Wed, 7 Oct 2009 13:51:07 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Nick Piggin <npiggin@...e.de>, Jens Axboe <jens.axboe@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	Ravikiran G Thirumalai <kiran@...lex86.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [rfc][patch] store-free path walking



On Wed, 7 Oct 2009, Andi Kleen wrote:
> 
> With some strategic prefetches it might be cheap enough to use 
> two cache lines. Just fetch it with the other.

I _seriously_ doubt that.

This is one of the biggest (and hottest) hash tables in the whole kernel.

No amount of prefetching will help the fact that you effectively double 
your cache footprint / working set if you have to fetch two cachelines in 
the hot case lookup rather than one.

			Linus
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