Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262627AbVCXKqJ (ORCPT ); Thu, 24 Mar 2005 05:46:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262772AbVCXKqJ (ORCPT ); Thu, 24 Mar 2005 05:46:09 -0500 Received: from mx1.elte.hu ([157.181.1.137]:47019 "EHLO mx1.elte.hu") by vger.kernel.org with ESMTP id S262627AbVCXKqC (ORCPT ); Thu, 24 Mar 2005 05:46:02 -0500 Date: Thu, 24 Mar 2005 11:45:54 +0100 From: Ingo Molnar To: Steven Rostedt Cc: linux-kernel@vger.kernel.org Subject: Re: [patch] Real-Time Preemption, -RT-2.6.12-rc1-V0.7.41-07 Message-ID: <20050324104554.GB20359@elte.hu> References: <20050322092331.GA21465@elte.hu> <20050322093201.GA21945@elte.hu> <20050322100153.GA23143@elte.hu> <20050322112856.GA25129@elte.hu> <20050323061601.GE1294@us.ibm.com> <20050323063317.GB31626@elte.hu> <20050324052854.GA1298@us.ibm.com> <20050324053456.GA14494@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-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1407 Lines: 36 * Steven Rostedt wrote: > I also see this with non rt tasks causing a burst of schedules. > > 1. Process A runs and grabs lock L. then finishes its time slice. > 2. Process B runs and tries to grab Lock L. > 3. Process A runs and releases lock L. > 4. __up_mutex gives process B lock L. > 5. Process A tries to grab lock L. > 6. Process B runs and releases lock L. > 7. __up_mutex gives lock L to process A. > 8. Process B tries to grab lock L again. > 9. Process A runs... > > Here we have more unnecessary schedules. So the condition to grab a lock > should be: > > 1. not owned. > 2. partially owned, and the owner is not RT. > 3. partially owned but the owner is RT and so is the grabber, and the > grabber's priority is >= the owner's priority. yeah, sounds good - but i'd not make any distinction between RT and non-RT tasks - just make the rule #3 distinction based on ->prio. In particular on UP a task should only run when its higher prio, so if a lock is 'partially owned' then the priority rule should always be true. (On SMP it's a bit more complex, there the priority rule could make a real difference.) 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/