From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751294AbWBPAji (ORCPT ); Wed, 15 Feb 2006 19:39:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751322AbWBPAjh (ORCPT ); Wed, 15 Feb 2006 19:39:37 -0500 Received: from omta03sl.mx.bigpond.com ([144.140.92.155]:27203 "EHLO omta03sl.mx.bigpond.com") by vger.kernel.org with ESMTP id S1751294AbWBPAjh (ORCPT ); Wed, 15 Feb 2006 19:39:37 -0500 Message-ID: <43F3C9C6.5080606@bigpond.net.au> Date: Thu, 16 Feb 2006 11:39:34 +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: Linux Kernel Mailing List , "Siddha, Suresh B" , npiggin@suse.de, Ingo Molnar , Steven Rostedt , Linus Torvalds , Con Kolivas Subject: [PATCH] Fix smpnice high priority task hopping problem Content-Type: multipart/mixed; boundary="------------010201090002030004050900" X-Authentication-Info: Submitted using SMTP AUTH PLAIN at omta03sl.mx.bigpond.com from [147.10.133.38] using ID pwil3058@bigpond.net.au at Thu, 16 Feb 2006 00:39:34 +0000 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------010201090002030004050900 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Suresh B. Siddha has reported: "on a lightly loaded system, this will result in higher priority job hopping around from one processor to another processor.. This is because of the code in find_busiest_group() which assumes that SCHED_LOAD_SCALE represents a unit process load and with nice_to_bias calculations this is no longer true (in the presence of non nice-0 tasks)" Analysis of this problem as revealed that the smpnice code results in the weighted load being larger than 1 and this triggers the active load balancing code. However, in active_load_balance(), the migration thread fails to take into account itself when deciding if there are any tasks to be migrated from its run queue. I.e. even if there is only one other task on the run queue other than itself it will still migrate that other task. The attached patch fixes that anomaly. Signed-off-by: Peter Williams Peter -- Peter Williams pwil3058@bigpond.net.au "Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce --------------010201090002030004050900 Content-Type: text/plain; name="fix-smpnice-task-hopping-problem" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="fix-smpnice-task-hopping-problem" Index: MM-2.6.X/kernel/sched.c =================================================================== --- MM-2.6.X.orig/kernel/sched.c 2006-02-16 10:51:52.000000000 +1100 +++ MM-2.6.X/kernel/sched.c 2006-02-16 11:02:45.000000000 +1100 @@ -2406,7 +2406,7 @@ static void active_load_balance(runqueue runqueue_t *target_rq; int target_cpu = busiest_rq->push_cpu; - if (busiest_rq->nr_running <= 1) + if (busiest_rq->nr_running <= 2) /* no task to move */ return; --------------010201090002030004050900--