From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933143AbXCAIx5 (ORCPT ); Thu, 1 Mar 2007 03:53:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933149AbXCAIx5 (ORCPT ); Thu, 1 Mar 2007 03:53:57 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:38506 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933143AbXCAIx4 (ORCPT ); Thu, 1 Mar 2007 03:53:56 -0500 Date: Thu, 1 Mar 2007 09:46:57 +0100 From: Ingo Molnar To: Mike Galbraith Cc: Con Kolivas , Michal Piotrowski , Thomas Gleixner , Adrian Bunk , Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: 2.6.21-rc1: known regressions (v2) (part 2) Message-ID: <20070301084657.GA31728@elte.hu> References: <200702281007.16316.kernel@kolivas.org> <1172636499.6534.101.camel@Homer.simpson.net> <200703010901.41715.kernel@kolivas.org> <1172707341.7027.95.camel@Homer.simpson.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1172707341.7027.95.camel@Homer.simpson.net> User-Agent: Mutt/1.4.2.2i X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.1.7 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Mike Galbraith wrote: > I see no real difference between the two assertions. Nice is just a > mechanism to set priority, so I applied your assertion to a different > range of priorities than nice covers, and returned it to show that the > code contradicts itself. It can't be bad for a nice 1 task to run > with a nice 0 task, but OK for a minimum RT task to run with a maximum > RT task. Iff HT without corrective measures breaks nice, then it > breaks realtime priorities as well. i'm starting to lean towards your view that we should not artificially keep tasks from running, when there's a free CPU available. We should still keep the 'other half' of SMT scheduling: the immediate pushing of tasks to a related core, but this bit of 'do not run tasks on this CPU' dependent-sleeper logic is i think a bit fragile. Plus these days SMT siblings do not tend to influence each other in such a negative way as older P4 ones where a HT sibling would slow down the other sibling significantly. plus with an increasing number of siblings (which seems like an inevitable thing on the hardware side), the dependent-sleeper logic becomes less and less scalable. We'd have to cross-check every other 'related' CPU's current priority to decide what to run. if then there should be a mechanism /in the hardware/ to set the priority of a CPU - and then the hardware could decide how to prioritize between siblings. Doing this in software is really hard. Ingo