From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031208AbXDSIeT (ORCPT ); Thu, 19 Apr 2007 04:34:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1031220AbXDSIeT (ORCPT ); Thu, 19 Apr 2007 04:34:19 -0400 Received: from cantor2.suse.de ([195.135.220.15]:44102 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031208AbXDSIeR (ORCPT ); Thu, 19 Apr 2007 04:34:17 -0400 Date: Thu, 19 Apr 2007 10:33:43 +0200 From: Nick Piggin To: Ingo Molnar Cc: Andrew Morton , Linus Torvalds , Matt Mackall , William Lee Irwin III , Peter Williams , Mike Galbraith , Con Kolivas , ck list , Bill Huey , linux-kernel@vger.kernel.org, Arjan van de Ven , Thomas Gleixner Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS] Message-ID: <20070419083343.GA14885@wotan.suse.de> References: <20070417070155.GF1057@wotan.suse.de> <20070417213954.GE11166@waste.org> <20070418031511.GA18452@wotan.suse.de> <20070418043831.GR11115@waste.org> <20070418050024.GF18452@wotan.suse.de> <20070418055525.GS11115@waste.org> <20070419031807.GA24512@wotan.suse.de> <20070418221432.e4dbcf4f.akpm@linux-foundation.org> <20070419063810.GA22418@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070419063810.GA22418@elte.hu> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 19, 2007 at 08:38:10AM +0200, Ingo Molnar wrote: > > * Andrew Morton wrote: > > > > And yes, by fairly, I mean fairly among all threads as a base > > > resource class, because that's what Linux has always done > > > > Yes, there are potential compatibility problems. Example: a machine > > with 100 busy httpd processes and suddenly a big gzip starts up from > > console or cron. > > > > Under current kernels, that gzip will take ages and the httpds will > > take a 1% slowdown, which may well be exactly the behaviour which is > > desired. > > > > If we were to schedule by UID then the gzip suddenly gets 50% of the > > CPU and those httpd's all take a 50% hit, which could be quite > > serious. > > > > That's simple to fix via nicing, but people have to know to do that, > > and there will be a transition period where some disruption is > > possible. > > hmmmm. How about the following then: default to nice -10 for all > (SCHED_NORMAL) kernel threads and all root-owned tasks. Root _is_ > special: root already has disk space reserved to it, root has special > memory allocation allowances, etc. I dont see a reason why we couldnt by > default make all root tasks have nice -10. This would be instantly loved > by sysadmins i suspect ;-) I have no problem with doing fancy new fairness classes and things. But considering that we _need_ to have per-thread fairness and that is also what the current scheduler has and what we need to do well for obvious reasons, the best path to take is to get per-thread scheduling up to a point where it is able to replace the current scheduler, then look at more complex things after that.