From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751342AbWDHALI (ORCPT ); Fri, 7 Apr 2006 20:11:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751368AbWDHALI (ORCPT ); Fri, 7 Apr 2006 20:11:08 -0400 Received: from omta04ps.mx.bigpond.com ([144.140.83.156]:33202 "EHLO omta04ps.mx.bigpond.com") by vger.kernel.org with ESMTP id S1751342AbWDHALH (ORCPT ); Fri, 7 Apr 2006 20:11:07 -0400 Message-ID: <4436FF98.3050604@bigpond.net.au> Date: Sat, 08 Apr 2006 10:11:04 +1000 From: Peter Williams User-Agent: Thunderbird 1.5 (X11/20060313) MIME-Version: 1.0 To: Ingo Molnar CC: Darren Hart , linux-kernel@vger.kernel.org, Thomas Gleixner , "Stultz, John" , "Siddha, Suresh B" , Nick Piggin Subject: Re: RT task scheduling References: <200604052025.05679.darren@dvhart.com> <20060406073753.GA18349@elte.hu> In-Reply-To: <20060406073753.GA18349@elte.hu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Authentication-Info: Submitted using SMTP AUTH PLAIN at omta04ps.mx.bigpond.com from [147.10.133.38] using ID pwil3058@bigpond.net.au at Sat, 8 Apr 2006 00:11:05 +0000 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Ingo Molnar wrote: > * Darren Hart wrote: > >> My last mail specifically addresses preempt-rt, but I'd like to know >> people's thoughts regarding this issue in the mainline kernel. Please >> see my previous post "realtime-preempt scheduling - rt_overload >> behavior" for a testcase that produces unpredictable scheduling >> results. > > the rt_overload feature i intend to push upstream-wards too, i just > didnt separate it out of -rt yet. > > "RT overload scheduling" is a totally orthogonal mechanism to the SMP > load-balancer (and this includes smpnice too) that is more or less > equivalent to having a 'global runqueue' for real-time tasks, without > the SMP overhead associated with that. If there is no "RT overload" [the > common case even on Linux systems that _do_ make use of RT tasks > occasionally], the new mechanism is totally inactive and there's no > overhead. But once there are more RT tasks than CPUs, the scheduler will > do "global" decisions for what RT tasks to run on which CPU. Is this good enough? Isn't it possible with the current try_to_wake_up() implementation (with or without smpnice) for two RT tasks to end up on the same CPU even when there are less RT tasks than CPUs? > To put even > less overhead on the mainstream kernel, i plan to introduce a new > SCHED_FIFO_GLOBAL scheduling policy to trigger this behavior. [it doesnt > make much sense to extend SCHED_RR in that direction.] I wouldn't have thought a new policy was necessary. Why not just do this for all SCHED_FIFO (or even all RT) tasks? BTW Does any body in the real world actually use SCHED_RR? Peter -- Peter Williams pwil3058@bigpond.net.au "Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce