Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758169AbZJHNMs (ORCPT ); Thu, 8 Oct 2009 09:12:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758122AbZJHNMr (ORCPT ); Thu, 8 Oct 2009 09:12:47 -0400 Received: from mail-fx0-f227.google.com ([209.85.220.227]:50148 "EHLO mail-fx0-f227.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758100AbZJHNMq (ORCPT ); Thu, 8 Oct 2009 09:12:46 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; b=SOY7wZdRV4FZunYXjZAAO6m7OK/urFL/ZXZuse7W/SvDfbDFQytl5B21XGhGaSm3G7 zs68S8ctlk17wbyz5mJE2X6DUHyCKF/ajcaPljAWzLpffXwrpYoIo1351ir91HfP364o Zrm4R70Ly/Uepgy9XmhZePhzzZ/dJEnBfOfEc= MIME-Version: 1.0 In-Reply-To: References: <20091006101414.GM5216@kernel.dk> <20091007164622.GX30316@wotan.suse.de> <87eipfymcv.fsf@basil.nowhere.org> <20091007210651.GB1656@one.firstfloor.org> Date: Thu, 8 Oct 2009 15:12:08 +0200 Message-ID: <1158166a0910080612h29d93d50y875d5305cd4d985f@mail.gmail.com> Subject: Re: [rfc][patch] store-free path walking From: Denys Vlasenko To: Linus Torvalds Cc: Andi Kleen , Nick Piggin , Jens Axboe , Linux Kernel Mailing List , linux-fsdevel@vger.kernel.org, Ravikiran G Thirumalai , Peter Zijlstra Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1210 Lines: 26 On Wed, Oct 7, 2009 at 11:57 PM, Linus Torvalds wrote: > This, btw, is exactly the kind of thing we saw with some of the > non-temporal work, when we used nontemporal stores to copy pages on COW > faults, or when doing pre-zeroing of pages. You get rid of some of the > hot-spots in the kernel, and you then replace them with user space taking > the cache misses in random spots instead. The kernel profile looks better, > and system time may go down, but actual performace never went down - you > just moved your cache miss cost from one place to another. A few years ago when K7s were not ancient yet, after hearing argument for and against non-temporal stores, I decided to finally figure it for myself. I tested kernel build workload on two kernels with the only one difference - clear_page with and without non-temporal stores. "Non-temporal stores" kernel was faster, not slower. Just a little bit, but reproducibly. -- vda -- 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/