From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 5 Jun 2002 14:08:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 5 Jun 2002 14:08:39 -0400 Received: from gateway-1237.mvista.com ([12.44.186.158]:29943 "EHLO av.mvista.com") by vger.kernel.org with ESMTP id ; Wed, 5 Jun 2002 14:07:19 -0400 Message-ID: <3CFE52D8.1A36682F@mvista.com> Date: Wed, 05 Jun 2002 11:05:12 -0700 From: george anzinger Organization: Monta Vista Software X-Mailer: Mozilla 4.77 [en] (X11; U; Linux 2.2.12-20b i686) X-Accept-Language: en MIME-Version: 1.0 To: Andi Kleen CC: Ian Collinson , "'Andrew Morton'" , Robert Love , Mike Kravetz , linux-kernel@vger.kernel.org, andrea@suse.de Subject: Re: realtime scheduling problems with 2.4 linux kernel >= 2.4.10 In-Reply-To: <20020605141755.A1410@averell> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andi Kleen wrote: > > On Wed, Jun 05, 2002 at 01:53:06PM +0200, Ian Collinson wrote: > > > > > Are there any potentially negative consequences of this fix, apart from > > those already mentioned? > > I don't think so. > > It could still fail when you install a prio=99, SCHED_FIFO process. > > > I certainly vote for this feature being preserved, as it is extremely useful > > for debugging realtime priority apps. FYI, we narrowed it down to breaking > > in either 2.4.10-pre11 or pre12. > > That was when the low latency console changes went in. Before that console > switches could interrupt scheduling for a long time, causing problems > for other realtime people. The change was to move the expensive parts > of the console switch to keventd. So that means that, with the above change to prio 99, we reintroduce the latency problem, only now it is in a task (keventd) and not an interrupt? (I know, I know, the work has to be done somewhere. At least this way we can control what priority level it is done at. I.e. this is a step in the right direction. I just what folks to be aware of the latency issue and where it is.) For what its worth, you can change the priority of keventd AFTER a system is up. Robert Love's real time tools contain a program (rt I think) that will do this for you. Just follow the URL for preemption in my sig. file and look around. -- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Real time sched: http://sourceforge.net/projects/rtsched/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml