From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752629AbaHTJr7 (ORCPT ); Wed, 20 Aug 2014 05:47:59 -0400 Received: from relay.parallels.com ([195.214.232.42]:59192 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751569AbaHTJrz (ORCPT ); Wed, 20 Aug 2014 05:47:55 -0400 Message-ID: <1408528070.23412.89.camel@tkhai> Subject: [PATCH v5 3/5] sched: Remove double_rq_lock() from __migrate_task() From: Kirill Tkhai To: CC: Peter Zijlstra , Paul Turner , Oleg Nesterov , Steven Rostedt , "Mike Galbraith" , Kirill Tkhai , "Tim Chen" , Ingo Molnar , "Nicolas Pitre" Date: Wed, 20 Aug 2014 13:47:50 +0400 In-Reply-To: <20140820092458.27076.30955.stgit@tkhai> References: <20140820092458.27076.30955.stgit@tkhai> Organization: Parallels Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.5-2+b3 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Originating-IP: [10.30.26.172] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Avoid double_rq_lock() and use TASK_ON_RQ_MIGRATING for __migrate_task(). The advantage is (obviously) not holding two 'rq->lock's at the same time and thereby increasing parallelism. The important point to note is that because we acquire dst->lock immediately after releasing src->lock the potential wait time of task_rq_lock() callers on TASK_ON_RQ_MIGRATING is not longer than it would have been in the double rq lock scenario. Signed-off-by: Kirill Tkhai --- kernel/sched/core.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index cef1a13..a50393b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4663,20 +4663,20 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr); */ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu) { - struct rq *rq_dest, *rq_src; + struct rq *rq; int ret = 0; if (unlikely(!cpu_active(dest_cpu))) return ret; - rq_src = cpu_rq(src_cpu); - rq_dest = cpu_rq(dest_cpu); + rq = cpu_rq(src_cpu); raw_spin_lock(&p->pi_lock); - double_rq_lock(rq_src, rq_dest); + raw_spin_lock(&rq->lock); /* Already moved. */ if (task_cpu(p) != src_cpu) goto done; + /* Affinity changed (again). */ if (!cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p))) goto fail; @@ -4686,15 +4686,22 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu) * placed properly. */ if (task_on_rq_queued(p)) { - dequeue_task(rq_src, p, 0); + dequeue_task(rq, p, 0); + p->on_rq = TASK_ON_RQ_MIGRATING; set_task_cpu(p, dest_cpu); - enqueue_task(rq_dest, p, 0); - check_preempt_curr(rq_dest, p, 0); + raw_spin_unlock(&rq->lock); + + rq = cpu_rq(dest_cpu); + raw_spin_lock(&rq->lock); + BUG_ON(task_rq(p) != rq); + p->on_rq = TASK_ON_RQ_QUEUED; + enqueue_task(rq, p, 0); + check_preempt_curr(rq, p, 0); } done: ret = 1; fail: - double_rq_unlock(rq_src, rq_dest); + raw_spin_unlock(&rq->lock); raw_spin_unlock(&p->pi_lock); return ret; }