From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761896AbXHBVIQ (ORCPT ); Thu, 2 Aug 2007 17:08:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761182AbXHBVFi (ORCPT ); Thu, 2 Aug 2007 17:05:38 -0400 Received: from wudika.de ([213.239.211.247]:48267 "EHLO wudika.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757777AbXHBVFg (ORCPT ); Thu, 2 Aug 2007 17:05:36 -0400 Message-ID: <46B2471C.5060801@felicis.org> Date: Thu, 02 Aug 2007 23:05:32 +0200 From: Martin Roehricht User-Agent: Thunderbird 1.5.0.12 (X11/20070604) MIME-Version: 1.0 To: Ingo Molnar CC: linux-kernel@vger.kernel.org Subject: Re: Scheduling the highest priority task References: <8KLFD-G9-5@gated-at.bofh.it> <46B19CA1.7050204@felicis.org> <20070802114012.GA4067@elte.hu> <46B1F182.3010608@felicis.org> <20070802150350.GA3030@elte.hu> <46B1F4BA.4010107@felicis.org> <20070802151916.GA8688@elte.hu> <46B1FC6D.7010202@felicis.org> <20070802194825.GA23245@elte.hu> In-Reply-To: <20070802194825.GA23245@elte.hu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 02.08.2007 21:48, Ingo Molnar wrote: > * Martin Roehricht wrote: > >> On 08/02/2007 05:19 PM, Ingo Molnar wrote: >> >* Martin Roehricht wrote: >> > >> >>That's fine with me, that within the same priority-queue any task can >> >>be chosen. But assume two tasks with highly different priorities, such >> >>as 105 and 135 are scheduled on the same processor and one of them is >> >>now to be migrated -- shouldn't be the queue with task P=105 >> >>considered first for migration by this code? Both tasks would use >> >>different queues with their own linked lists, right? >> > >> >yes. What makes you believe that the lower priority one (prio 135) is >> >chosen? [ as i said before, that will only be chosen if all tasks in the >> >higher-priority queue (prio 105) are either already running on a CPU or >> >have recently run so that the cache-hot logic skips them. ] >> >> This believe is primarily based on my observations of multiple >> benchmark runs and also on your statement earlier: ģin the SMP >> migration code, the 'old scheduler' indeed picks the lowest priority >> oneĢ. > > oh, sorry, that was meant to be the 'highest priority one' :-/ > > so i think you got it all right, i just typoed that first sentence. Okay, now I think I understood this part of the code correctly. The reason why I observe a continous migration of the _lower_ priority tasks is most probably due to the fact that the higher priority one is currently running, according to: can_migrate_task() in move_tasks(), and therein: if (task_running(rq, p)) return 0; I tracked down via an extended /proc/schedstats that my tasks fall frequently into this pitfall. I basically solved it by making use of the more active push-strategy which is called later by load_balance() once the move_tasks() function did not succeed. So in case I need the higher priority tasks, I return immediately from move_tasks(). Thanks for your help, Martin