From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755812AbcIRCHm (ORCPT ); Sat, 17 Sep 2016 22:07:42 -0400 Received: from mail-pa0-f68.google.com ([209.85.220.68]:33717 "EHLO mail-pa0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755345AbcIRCHe (ORCPT ); Sat, 17 Sep 2016 22:07:34 -0400 Subject: Re: [PATCH v4] stop_machine: Avoid a sleep and wakeup in the stop_one_cpu() To: peterz@infradead.org References: <1473497532-5440-1-git-send-email-cs.os.kernel@gmail.com> <1473818510-6779-1-git-send-email-cs.os.kernel@gmail.com> Cc: mingo@kernel.org, oleg@redhat.com, tj@kernel.org, akpm@linux-foundation.org, chris@chris-wilson.co.uk, linux-kernel@vger.kernel.org From: Cheng Chao Message-ID: <61f8640f-1530-467b-fb9e-ba8028c075ab@gmail.com> Date: Sun, 18 Sep 2016 10:07:30 +0800 User-Agent: Mozilla/5.0 (X11; Linux i686; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: <1473818510-6779-1-git-send-email-cs.os.kernel@gmail.com> Content-Type: text/plain; charset=gbk Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, What should I do next? Thanks. Cheng on 09/14/2016 10:01 AM, Cheng Chao wrote: > In case @cpu == smp_proccessor_id(), we can avoid a sleep+wakeup > by doing a preemption. > > the caller such as sched_exec can benefit from this change. > > Signed-off-by: Cheng Chao > Cc: Oleg Nesterov > Cc: Peter Zijlstra > --- > 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 a0086a5..283b662 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..1a24890 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 > + * by doing a preemption. > + */ > + cond_resched(); > wait_for_completion(&done.completion); > return done.ret; > } >