Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750816AbWBMQNS (ORCPT ); Mon, 13 Feb 2006 11:13:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750819AbWBMQNS (ORCPT ); Mon, 13 Feb 2006 11:13:18 -0500 Received: from mtagate1.de.ibm.com ([195.212.29.150]:45252 "EHLO mtagate1.de.ibm.com") by vger.kernel.org with ESMTP id S1750816AbWBMQNQ (ORCPT ); Mon, 13 Feb 2006 11:13:16 -0500 Date: Mon, 13 Feb 2006 17:13:03 +0100 From: Heiko Carstens To: Ingo Molnar Cc: Hannes Reinecke , linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: calibrate_migration_costs takes ages on s390 Message-ID: <20060213161303.GA9315@osiris.boeblingen.de.ibm.com> References: <20060213102634.GA4677@osiris.boeblingen.de.ibm.com> <20060213104645.GA17173@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060213104645.GA17173@elte.hu> User-Agent: mutt-ng/devel (Linux) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1706 Lines: 36 > > The boot sequence on s390 sometimes takes ages and we spend a very > > long time (up to one or two minutes) in calibrate_migration_costs. The > > time spent there differs from boot to boot. Also the calculated costs > > differ a lot. I've seen differences by up to a factor of 15 (yes, > > factor not percent). Also I doubt that making these measurements make > > much sense on a completely virtualized architecture where you cannot > > tell how much cpu time you will get anyway. Is there any workaround or > > fix available so we can avoid seeing this? > > which is the precise kernel version used? We toned down calibration a > bit recently. 2.6.16-rc3. > The immediate workaround would be to use the migration_cost=0 boot > parameter. > > Generally, i agree that it makes sense to not calibrate at all on > virtual platforms. Does the patch below help? It gives virtual > platforms a way to provide a default migration cost and thus avoid the > boot-time calibration altogether. (I have tested it on x86, it does the > expected thing.) This needs to hit v2.6.16 too. Yes, calibrate_migration_costs is very fast now. But it turned out that this was just hiding the real problem: if we have CONFIG_PREEMPT disabled the kernel gets (sometimes) unbelievably slow. I think this happened somewhere between rc1 and rc3. Maybe Hannes knows more exactly when this happened the first time, since I always run with CONFIG_PREEMPT enabled. Heiko - 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/