From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: RFC: THE OFFLINE SCHEDULER Date: Wed, 26 Aug 2009 23:08:12 +0200 Message-ID: <20090826210812.GA22765@elte.hu> References: <1251297910.1791.22.camel@maxim-laptop> <1251298443.4791.7.camel@raz> <1251300625.18584.18.camel@twins> <1251302598.18584.31.camel@twins> <20090826180407.GA13632@elte.hu> <20090826193252.GA14721@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Peter Zijlstra , raz ben yehuda , Maxim Levitsky , Chris Friesen , Mike Galbraith , riel@redhat.com, andrew motron , wiseman@macs.biu.ac.il, lkml , linux-rt-users@vger.kernel.org To: Christoph Lameter Return-path: Received: from mx3.mail.elte.hu ([157.181.1.138]:46727 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751548AbZHZVIl (ORCPT ); Wed, 26 Aug 2009 17:08:41 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: * Christoph Lameter wrote: > > to have sharp teeth nor any apparent poison fangs) - i simply > > concur with the reasons Peter listed that it is a technically > > inferior solution. > > Ok so you are saying that the reduction of OS latencies will make > the processor completely available and have no disturbances like > OFFLINE scheduling? I'm saying that your lack of trying to reduce even low-hanging-fruit latency sources that were pointed out to you fundamentally destroys your credibility in claiming that they are unfixable for all practical purposes. Or, to come up with a car analogy: it's a bit as if at a repair shop you complained that your car has a scratch on its cooler grid that annoys you, and you insisted that it be outfitted with a new diesel engine which needs no cooler grid (throwing away the nice Hemi block it has currently) - and ignored the mechanic's opinion that he loves the Hemi and that to him the scratch looks very much like bird-sh*t and that a proper car wash might do the trick too ;-) > Peter has not given a solution to the problem. Nor have you. What do you mean by 'has given a solution' - a patch? Peter mentioned a few things that you can try to reduce the worst-case latency of the timer tick. Peter also implemented the hr-tick solution (CONFIG_SCHED_HRTICK) - it's mostly upstream but disabled because it had problems - if you are interested in improving this area you can fix and complete it. That would benefit ordinary Linux users too, not just rare isolation apps. Ingo