From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757121AbZECXZb (ORCPT ); Sun, 3 May 2009 19:25:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756983AbZECXZA (ORCPT ); Sun, 3 May 2009 19:25:00 -0400 Received: from yw-out-2324.google.com ([74.125.46.28]:5853 "EHLO yw-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756935AbZECXY7 convert rfc822-to-8bit (ORCPT ); Sun, 3 May 2009 19:24:59 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:from:date :x-google-sender-auth:message-id:subject:to:cc:content-type :content-transfer-encoding; b=E/3QuqoVRUFPibmSxjqaIBPY0m1Y2fHQzsqbnt91tRL0lTxWb6rjz/Rd3i3e4EDR8O J5Y1YS25Q9umILTIGNf90gJF9nUPuqg1xtNjtNnm/qwknwlSM3aMgCEEcufS40EmStWA kQFxhupYx+d1pf7TFUTjGR1E0pHCrB5lIxju8= MIME-Version: 1.0 In-Reply-To: <49FDEFD1.8020608@nico22.de> References: <49FDEFD1.8020608@nico22.de> From: Ray Lee Date: Sun, 3 May 2009 16:24:43 -0700 X-Google-Sender-Auth: d6d1f896cb752c8f Message-ID: <2c0942db0905031624p350f37c8i1efa1b2654e7b7fe@mail.gmail.com> Subject: Re: CFS not suitable for desktop computers To: =?UTF-8?Q?Nico_Sch=C3=BCmann?= , Ingo Molnar , Peter Zijlstra Cc: linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, May 3, 2009 at 12:26 PM, Nico Schümann wrote: > Dear Linux developers, > > I have been using Linux for some years now and for me, the best thing about > 2.6 was that Linux ran desktop applications just smoothly. I was able to > compile in the background, while all applications under X11 were just usable > as if the machine was in idle mode. This was due to the priority of gcc > being set to 30, for instance. > > Then, somewhere around 2.6.19 or 2.6.21, I do not remember exactly, the CFS > was introduced, which removed all those "latency-based" scheduling policies. > Now that I use 2.6.29 (I did not write earlier because I though it was a > regression issue) I have to say: Linux is not as perfectly usable as before. > End users do not want to experiment with nice levels and stuff, they just > want that the system stays responsible even if there is a cpu-consuming > process in the _background_. For me, this had been the greatest benefit from > using Linux . > > Now what can we do, so that foreground applications are smoothly usable > during hard cpu load? Is there any way to restore the old behaviour that > cpu-consuming processes get a lower priority? It had always worked until > this new scheduler was introduced. My experience is exactly the opposite. Before CFS, my system was completely unusable unless I manually controlled all nice levels in the system for the big jobs. With CFS, everything just works, no twiddling of nice levels necessary. To get a useful response from the developers (who really do care about latency issues), you should run a workload that causes unacceptable behavior, and follow the suggestions below (taken from an old email from Ingo Molnar): ---------- could you run this script while such a slowdown is really prominent: http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh and send me the output it generates? The output is the most useful if you do this on a kernel that has CONFIG_SCHED_DEBUG=y and CONFIG_SCHEDSTATS=y enabled. ---------- The problem may not be related to the scheduler at all, you realize, but rather some other regression in another subsystem, such as the IO scheduler or X or a driver, but hopefully the above script will be a good starting point for those with the big brains to figure out what's wrong.