Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751685AbdHaL7B (ORCPT ); Thu, 31 Aug 2017 07:59:01 -0400 Received: from foss.arm.com ([217.140.101.70]:55116 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751456AbdHaL6c (ORCPT ); Thu, 31 Aug 2017 07:58:32 -0400 From: Brendan Jackman To: Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org Cc: Dietmar Eggemann , Vincent Guittot , Josef Bacik , Morten Rasmussen Subject: [PATCH v3 4/5] sched/fair: Fix use of find_idlest_group when no groups are allowed Date: Thu, 31 Aug 2017 12:58:01 +0100 Message-Id: <20170831115802.26365-5-brendan.jackman@arm.com> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20170831115802.26365-1-brendan.jackman@arm.com> References: <20170831115802.26365-1-brendan.jackman@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1684 Lines: 47 When p is allowed on none of the CPUs in the sched_domain, we currently return NULL from find_idlest_group, and pointlessly continue the search on lower sched_domain levels (where p is also not allowed) before returning prev_cpu regardless (as we have not updated new_cpu). Add an explicit check for this case, and a comment to find_idlest_group. Now when find_idlest_group returns NULL, it always means that the local group is allowed and idlest. Signed-off-by: Brendan Jackman Cc: Dietmar Eggemann Cc: Vincent Guittot Cc: Josef Bacik Cc: Ingo Molnar Cc: Morten Rasmussen Cc: Peter Zijlstra Reviewed-by: Vincent Guittot --- kernel/sched/fair.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0ce75bb..2608091 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5380,6 +5380,8 @@ static unsigned long capacity_spare_wake(int cpu, struct task_struct *p) /* * find_idlest_group finds and returns the least busy CPU group within the * domain. + * + * Assumes p is allowed on at least one CPU in sd. */ static struct sched_group * find_idlest_group(struct sched_domain *sd, struct task_struct *p, @@ -5567,6 +5569,9 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p { int new_cpu = prev_cpu; + if (!cpumask_intersects(sched_domain_span(sd), &p->cpus_allowed)) + return prev_cpu; + while (sd) { struct sched_group *group; struct sched_domain *tmp; -- 2.7.4