Messages in this thread | | | Date | Wed, 14 Sep 2016 17:53:45 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v4] stop_machine: Avoid a sleep and wakeup in the stop_one_cpu() |
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On 09/14, Cheng Chao wrote: > > --- 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; > + }
Cough ;) again, I leave this to Peter...
But imo this change should be documented or perhaps even separated. It looks fine to me, but this has nothing to do with "we can avoid a sleep+wakeup by doing a preemption" from the changelog.
This is another improvement, and a small note in the changelog can unconfuse the reader of git blame/log.
Oleg.
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