Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759978AbZJGUxJ (ORCPT ); Wed, 7 Oct 2009 16:53:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758180AbZJGUxI (ORCPT ); Wed, 7 Oct 2009 16:53:08 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:53851 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756706AbZJGUxH (ORCPT ); Wed, 7 Oct 2009 16:53:07 -0400 Date: Wed, 7 Oct 2009 13:51:07 -0700 (PDT) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Andi Kleen cc: Nick Piggin , Jens Axboe , Linux Kernel Mailing List , linux-fsdevel@vger.kernel.org, Ravikiran G Thirumalai , Peter Zijlstra Subject: Re: [rfc][patch] store-free path walking In-Reply-To: <87eipfymcv.fsf@basil.nowhere.org> Message-ID: References: <20091006064919.GB30316@wotan.suse.de> <20091006101414.GM5216@kernel.dk> <20091006122623.GE30316@wotan.suse.de> <20091006124941.GS5216@kernel.dk> <20091007085849.GN30316@wotan.suse.de> <20091007164622.GX30316@wotan.suse.de> <87eipfymcv.fsf@basil.nowhere.org> User-Agent: Alpine 2.01 (LFD 1184 2008-12-16) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 701 Lines: 21 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/