From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751330AbWBQCvt (ORCPT ); Thu, 16 Feb 2006 21:51:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751335AbWBQCvt (ORCPT ); Thu, 16 Feb 2006 21:51:49 -0500 Received: from omta01sl.mx.bigpond.com ([144.140.92.153]:24269 "EHLO omta01sl.mx.bigpond.com") by vger.kernel.org with ESMTP id S1751330AbWBQCvs (ORCPT ); Thu, 16 Feb 2006 21:51:48 -0500 Message-ID: <43F53A42.2090909@bigpond.net.au> Date: Fri, 17 Feb 2006 13:51:46 +1100 From: Peter Williams User-Agent: Mozilla Thunderbird 1.0.7-1.1.fc4 (X11/20050929) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andrew Morton CC: "Siddha, Suresh B" , Linux Kernel Mailing List , npiggin@suse.de, Ingo Molnar , Steven Rostedt , Linus Torvalds , Con Kolivas Subject: Re: [PATCH] Fix smpnice high priority task hopping problem References: <43F3C9C6.5080606@bigpond.net.au> <20060216171357.A27025@unix-os.sc.intel.com> <43F53553.50904@bigpond.net.au> In-Reply-To: <43F53553.50904@bigpond.net.au> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Authentication-Info: Submitted using SMTP AUTH PLAIN at omta01sl.mx.bigpond.com from [147.10.133.38] using ID pwil3058@bigpond.net.au at Fri, 17 Feb 2006 02:51:46 +0000 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Peter Williams wrote: > Siddha, Suresh B wrote: > >> Andrew, Please don't apply this patch. This breaks the existing HT >> (and multi-core) scheduler optimizations. >> >> Peter, on a DP system with HT, if we have only two runnable processes >> and they end up running on the two threads of the same package, with >> your patch, migration thread will never move one of those processes to >> the idle package.. > > > On a normal system, would either of them be moved anyway? > >> >> To fix my reported problem, we need to make sure that >> find_busiest_group() >> doesn't find an imbalance.. > > > I disagree. If this causes a problem with your "optimizations" then I > think that you need to fix the "optimizations". > > There's a rational argument (IMHO) that this patch should be applied > even in the absence of the smpnice patches as it prevents > active_load_balance() doing unnecessary work. If this isn't good for > hypo threading then hypo threading is a special case and needs to handle > it as such. OK. The good news is that (my testing shows that) the "sched: fix smpnice abnormal nice anomalies" fixes the imbalance problem and the consequent CPU hopping. BUT I still think that this patch (modified if necessary to handle any HT special cases) should be applied. On a normal system, it will (as I've already said) stop active_load_balance() from doing a lot of unnecessary work INCLUDING holding the run queue locks for TWO run queues for no good reason. Peter -- Peter Williams pwil3058@bigpond.net.au "Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce