Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753799AbZJGVWr (ORCPT ); Wed, 7 Oct 2009 17:22:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752944AbZJGVWr (ORCPT ); Wed, 7 Oct 2009 17:22:47 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:34704 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753694AbZJGVWp (ORCPT ); Wed, 7 Oct 2009 17:22:45 -0400 Date: Wed, 7 Oct 2009 14:20:50 -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: <20091007210651.GB1656@one.firstfloor.org> Message-ID: References: <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> <20091007210651.GB1656@one.firstfloor.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: 951 Lines: 28 On Wed, 7 Oct 2009, Andi Kleen wrote: > > It won't double it, because there are many more cache lines from > all kinds of other things in these paths. Not all that many. The big part of the D$ is the hash table lookup in this path. > The point was just to hide the latency of fetching two at different > times. The actual cache foot print is not that important, as long as > it's not excessive You're full of sh*t. Every extra line you fetch pushes out another line. No amount of prefetching will hide that. So stop spreading idiotic fairytales. The best optimization is to not do the work at all. It really is that simple. Prefetching as an optimization technique absolutely sucks. 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/