From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934831AbcIVOAI (ORCPT ); Thu, 22 Sep 2016 10:00:08 -0400 Received: from terminus.zytor.com ([198.137.202.10]:56666 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933098AbcIVOAD (ORCPT ); Thu, 22 Sep 2016 10:00:03 -0400 Date: Thu, 22 Sep 2016 06:59:24 -0700 From: tip-bot for Cheng Chao Message-ID: Cc: linux-kernel@vger.kernel.org, oleg@redhat.com, tglx@linutronix.de, mingo@kernel.org, hpa@zytor.com, torvalds@linux-foundation.org, cs.os.kernel@gmail.com, peterz@infradead.org Reply-To: peterz@infradead.org, cs.os.kernel@gmail.com, torvalds@linux-foundation.org, mingo@kernel.org, hpa@zytor.com, tglx@linutronix.de, oleg@redhat.com, linux-kernel@vger.kernel.org In-Reply-To: <1473818510-6779-1-git-send-email-cs.os.kernel@gmail.com> References: <1473818510-6779-1-git-send-email-cs.os.kernel@gmail.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] stop_machine: Avoid a sleep and wakeup in stop_one_cpu() Git-Commit-ID: bf89a304722f6904009499a31dc68ab9a5c9742e X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: bf89a304722f6904009499a31dc68ab9a5c9742e Gitweb: http://git.kernel.org/tip/bf89a304722f6904009499a31dc68ab9a5c9742e Author: Cheng Chao AuthorDate: Wed, 14 Sep 2016 10:01:50 +0800 Committer: Ingo Molnar CommitDate: Thu, 22 Sep 2016 14:53:45 +0200 stop_machine: Avoid a sleep and wakeup in stop_one_cpu() In case @cpu == smp_proccessor_id(), we can avoid a sleep+wakeup cycle by doing a preemption. Callers such as sched_exec() can benefit from this change. Signed-off-by: Cheng Chao Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: akpm@linux-foundation.org Cc: chris@chris-wilson.co.uk Cc: tj@kernel.org Link: http://lkml.kernel.org/r/1473818510-6779-1-git-send-email-cs.os.kernel@gmail.com Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 8 ++++++-- kernel/stop_machine.c | 5 +++++ 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c5f020c..ff4e3c0 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1063,8 +1063,12 @@ static int migration_cpu_stop(void *data) * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because * we're holding p->pi_lock. */ - if (task_rq(p) == rq && task_on_rq_queued(p)) - rq = __migrate_task(rq, p, arg->dest_cpu); + if (task_rq(p) == rq) { + if (task_on_rq_queued(p)) + rq = __migrate_task(rq, p, arg->dest_cpu); + else + p->wake_cpu = arg->dest_cpu; + } raw_spin_unlock(&rq->lock); raw_spin_unlock(&p->pi_lock); diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 4a1ca5f..082e71f 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -126,6 +126,11 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg) cpu_stop_init_done(&done, 1); if (!cpu_stop_queue_work(cpu, &work)) return -ENOENT; + /* + * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup + * cycle by doing a preemption: + */ + cond_resched(); wait_for_completion(&done.completion); return done.ret; }