Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750806AbVJJOE1 (ORCPT ); Mon, 10 Oct 2005 10:04:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750803AbVJJOE1 (ORCPT ); Mon, 10 Oct 2005 10:04:27 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:53987 "EHLO mx3.mail.elte.hu") by vger.kernel.org with ESMTP id S1750806AbVJJOE1 (ORCPT ); Mon, 10 Oct 2005 10:04:27 -0400 Date: Mon, 10 Oct 2005 16:04:20 +0200 From: Ingo Molnar To: Roman Zippel Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, Andrew Morton , george@mvista.com, johnstul@us.ibm.com, paulmck@us.ibm.com, Christoph Hellwig , oleg@tv-sign.ru, tim.bird@am.sony.com Subject: Re: [PATCH] ktimers subsystem 2.6.14-rc2-kt5 Message-ID: <20051010140420.GA30736@elte.hu> References: <20050928224419.1.patchmail@tglx.tec.linutronix.de> <20051001112233.GA18462@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i X-ELTE-SpamScore: 0.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=AWL autolearn=disabled SpamAssassin version=3.0.3 0.0 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1529 Lines: 33 * Roman Zippel wrote: > > > Do you have any numbers (besides maybe microbenchmarks) that show a > > > real advantage by using per cpu data? What kind of usage do you expect > > > here? > > > > it has countless advantages, and these days we basically only design > > per-CPU data structures within the kernel, unless some limitation (such > > as API or hw property) forces us to do otherwise. So i turn around the > > question: what would be your reason for _not_ doing this clean per-CPU > > design for SMP systems? > > Did I say I'm against it? No, I was just hoping someone put some more > thought into it than just "all the other kids are doing it". I was > just curious how well it really scales compared to the simple version, > e.g. what happens if most timer end up on a single cpu or what happens > if we want to start the timer on a different cpu. Is this so wrong > that you have to go into attack mode? :( [ sorry, and i didnt go into 'attack mode'. I believe you'll distinctly notice when i do that :-) ] just think NUMA, and the generic advantages of PER_CPU become obvious. (via PER_CPU the different data structures indexed can properly end up on another domain's RAM, and can thus improve caching characteristics.) Ingo - 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/