From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753605AbYHPQZn (ORCPT ); Sat, 16 Aug 2008 12:25:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752289AbYHPQZf (ORCPT ); Sat, 16 Aug 2008 12:25:35 -0400 Received: from server03.ke-net.com ([84.19.168.8]:49683 "EHLO server03.ke-net.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752204AbYHPQZe (ORCPT ); Sat, 16 Aug 2008 12:25:34 -0400 Subject: Re: SCHED_FIFO and SCHED_RR broken by cfs From: Stefani Seibold To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@redhat.com In-Reply-To: <1218898413.10800.252.camel@twins> References: <1218880552.11912.9.camel@matrix> <1218898413.10800.252.camel@twins> Content-Type: text/plain Date: Sat, 16 Aug 2008 18:26:37 +0200 Message-Id: <1218903997.3665.6.camel@matrix> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I haved tried your suggestion on my 2.6.26 pentium notebook. Nothing is changing. After applying 'echo -1> /proc/sys/kernel/sched_rt_runtime_us' the SCHED_FIFO jitter are still higher than with SCHED_OTHER. Here are the results of my notebook time chrt -f 99 /tmp/a.out time chrt -o 0 /tmp/a.out average: 212 average: 13 min. jitter: 0 usec min. jitter: 0 usec max. jitter: 50013 usec max. jitter: 33 usec The kernel was startet with init=/bin/bash, so no other process is running. Thanx for supporting me. Am Samstag, den 16.08.2008, 16:53 +0200 schrieb Peter Zijlstra: > On Sat, 2008-08-16 at 11:55 +0200, Stefani Seibold wrote: > > Hi kernel hackers, > > > > it seems that the new completely fair scheduler breaks the SCHED_RR and > > SCHED_FIFO realtime scheduler. > > > > In my opinion a high priority real time user process with SCHED_FIFO > > should be only interrupted by the kernel or a process with an higher > > priority. So a user process running under SCHED_FIFO and priority 99 > > should never be interrupted by any other process. This was true under > > kernel 2.6.20. > > > > On my pentium/celeron III/400 MHz system with kernel 2.6.20 a busy loop > > using the "time stamp counter" of the x86 cpu for delaying, this was > > very accurate. The max. jitter of the delaying was about 5 microseconds. > > > > With the new kernel 2.6.26 the jitter is about 51177 microseconds or in > > other words 51 milliseconds or more the 10000 times greater than kernel > > 2.6.20. This huge latency is far away from realtime. > > > > Below are the results of the attached test program. Maybe somebody else > > can confirm this results. All measurements was done with no other > > process running, only the busybox 1.11.1 shell and the init process was > > there. > > Has nothing to do with CFS, but everything to do with the fact that we > now have a 95% bandwidth control by default. > > Does doing: > > echo -1 > /proc/sys/kernel/sched_rt_runtime_us > > fix it? > > So, up to 95% cpu usage (per sched_rt_period_us) FIFO and RR behave like > they always did, once they cross that line, they'll be throttled. > > 95% seemed like a sane default in that it leaves a little room to > recover from a run-away rt process (esp handy now that !root users can > also use RT scheduling classes), and should be enough for most > applications as they usually don't consume all that much time. > > >