Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753504AbZJIHr6 (ORCPT ); Fri, 9 Oct 2009 03:47:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753010AbZJIHr6 (ORCPT ); Fri, 9 Oct 2009 03:47:58 -0400 Received: from cantor2.suse.de ([195.135.220.15]:42827 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752917AbZJIHr5 (ORCPT ); Fri, 9 Oct 2009 03:47:57 -0400 Date: Fri, 9 Oct 2009 09:47:19 +0200 From: Nick Piggin To: Denys Vlasenko Cc: Linus Torvalds , Andi Kleen , Jens Axboe , Linux Kernel Mailing List , linux-fsdevel@vger.kernel.org, Ravikiran G Thirumalai , Peter Zijlstra Subject: Re: [rfc][patch] store-free path walking Message-ID: <20091009074719.GE2983@wotan.suse.de> References: <20091007164622.GX30316@wotan.suse.de> <87eipfymcv.fsf@basil.nowhere.org> <20091007210651.GB1656@one.firstfloor.org> <1158166a0910080612h29d93d50y875d5305cd4d985f@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1158166a0910080612h29d93d50y875d5305cd4d985f@mail.gmail.com> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1723 Lines: 34 On Thu, Oct 08, 2009 at 03:12:08PM +0200, Denys Vlasenko wrote: > 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. It is going to be highly dependent on architecture and workload and exactly where you use the nontemporal stores of course. I would say with non-temporal stores in clear_page (a case where we can often expect the memory to be used again quickly because it is anonymous process memory), then we are quite likely to cause _more_ activity on the memory controller and dimms which cost far more power than cache access. -- 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/