From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753353AbYIEMaz (ORCPT ); Fri, 5 Sep 2008 08:30:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752154AbYIEMar (ORCPT ); Fri, 5 Sep 2008 08:30:47 -0400 Received: from E23SMTP04.au.ibm.com ([202.81.18.173]:55276 "EHLO e23smtp04.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751659AbYIEMaq (ORCPT ); Fri, 5 Sep 2008 08:30:46 -0400 Date: Fri, 5 Sep 2008 18:00:04 +0530 From: Gautham R Shenoy To: Peter Zijlstra , Vaidyanathan Srinivasan , Balbir Singh , Ingo Molnar Cc: linux-kernel@vger.kernel.org, Dipankar Sarma Subject: [PATCH] sched: Fix __load_balance_iterator() for cfq with only one task Message-ID: <20080905123004.GD6238@in.ibm.com> Reply-To: ego@in.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org sched: Fix __load_balance_iterator() for cfq with only one task. From: Gautham R Shenoy The __load_balance_iterator() returns a NULL when there's only one sched_entity which is a task. It is caused by the following code-path. /* Skip over entities that are not tasks */ do { se = list_entry(next, struct sched_entity, group_node); next = next->next; } while (next != &cfs_rq->tasks && !entity_is_task(se)); if (next == &cfs_rq->tasks) return NULL; ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This will return NULL even when se is a task. As a side-effect, there was a regression in sched_mc behavior since 2.6.25, since iter_move_one_task() when it calls load_balance_start_fair(), would not get any tasks to move! Fix this by checking if the last entity was a task or not. Signed-off-by: Gautham R Shenoy Cc: Peter Zijlstra Cc: Vaidyanathan Srinivasan Cc: Ingo Molnar --- kernel/sched_fair.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index fb8994c..f1c96e3 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -1451,7 +1451,7 @@ __load_balance_iterator(struct cfs_rq *cfs_rq, struct list_head *next) next = next->next; } while (next != &cfs_rq->tasks && !entity_is_task(se)); - if (next == &cfs_rq->tasks) + if (next == &cfs_rq->tasks && !entity_is_task(se)) return NULL; cfs_rq->balance_iterator = next; -- Thanks and Regards gautham