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Groups > linux.kernel > #1479989
| From | Oleg Nesterov <oleg@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v2] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE |
| Date | 2016-09-09 15:20 +0200 |
| Message-ID | <sftSO-3gY-17@gated-at.bofh.it> (permalink) |
| References | <sfpct-qw-3@gated-at.bofh.it> <sfpct-qw-1@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 09/09, Cheng Chao wrote: > > If the migration_cpu_stop() can not migrate,why do we call stop_one_cpu()? > It just makes the task TASK_UNINTERRUPTIBLE, wakes up the stopper thread, > executes migration_cpu_stop(), and the stopper thread wakes up the task. and this finally migrates the target, ttwu() does another select_task_rq(). > This patch keeps the task TASK_RUNNING instead of TASK_UNINTERRUPTIBLE, > so the migration_cpu_stop() can do useful works. yes, this avoids the extra wakeup/select_task_rq. So this is the minor optimization. > Signed-off-by: Cheng Chao <chengchao@kedacom.com> > --- > kernel/stop_machine.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c > index 4a1ca5f..41aea5e 100644 > --- a/kernel/stop_machine.c > +++ b/kernel/stop_machine.c > @@ -126,6 +126,17 @@ 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; > + > +#if defined(CONFIG_PREEMPT_NONE) > + /* > + * Makes the stopper thread run as soon as possible. > + * And if the caller is TASK_RUNNING, keeps the caller TASK_RUNNING. > + * It's special useful for some callers which are expected to be > + * TASK_ON_RQ_QUEUED. > + * sched_exec does benefit from this improvement. > + */ > + schedule(); Well. This can help in general, wait_for_completion() won't block, but only if we queue the work on the same CPU. Otherwise this schedule() adds the unnecessary pessimization. That is why I suggested to use _cond_resched() instead of schedule(). But let me repeat, I leave this to maintainers. Oleg.
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[PATCH v2] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Cheng Chao <chengchao@kedacom.com> - 2016-09-09 10:20 +0200
Re: [PATCH v2] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE chengchao <chengchao@kedacom.com> - 2016-09-09 10:20 +0200
Re: [PATCH v2] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Oleg Nesterov <oleg@redhat.com> - 2016-09-09 15:20 +0200
Re: [PATCH v2] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Peter Zijlstra <peterz@infradead.org> - 2016-09-09 18:30 +0200
[PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Cheng Chao <cs.os.kernel@gmail.com> - 2016-09-10 11:00 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Cheng Chao <cs.os.kernel@gmail.com> - 2016-09-10 12:00 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Peter Zijlstra <peterz@infradead.org> - 2016-09-10 18:40 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Oleg Nesterov <oleg@redhat.com> - 2016-09-12 13:10 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Cheng Chao <cs.os.kernel@gmail.com> - 2016-09-13 04:50 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Peter Zijlstra <peterz@infradead.org> - 2016-09-12 13:40 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Peter Zijlstra <peterz@infradead.org> - 2016-09-12 13:50 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Oleg Nesterov <oleg@redhat.com> - 2016-09-12 15:10 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Peter Zijlstra <peterz@infradead.org> - 2016-09-12 17:10 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Oleg Nesterov <oleg@redhat.com> - 2016-09-13 18:20 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Peter Zijlstra <peterz@infradead.org> - 2016-09-13 18:40 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Cheng Chao <cs.os.kernel@gmail.com> - 2016-09-14 04:10 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Peter Zijlstra <peterz@infradead.org> - 2016-09-14 10:00 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Oleg Nesterov <oleg@redhat.com> - 2016-09-14 17:50 +0200
[tip:sched/core] sched/core: Optimize __schedule() tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2016-09-22 16:10 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Cheng Chao <cs.os.kernel@gmail.com> - 2016-09-13 06:10 +0200
Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Peter Zijlstra <peterz@infradead.org> - 2016-09-13 10:50 +0200
[PATCH v4] stop_machine: Avoid a sleep and wakeup in the stop_one_cpu() Cheng Chao <cs.os.kernel@gmail.com> - 2016-09-14 04:10 +0200
Re: [PATCH v4] stop_machine: Avoid a sleep and wakeup in the stop_one_cpu() Oleg Nesterov <oleg@redhat.com> - 2016-09-14 18:00 +0200
Re: [PATCH v4] stop_machine: Avoid a sleep and wakeup in the stop_one_cpu() Cheng Chao <cs.os.kernel@gmail.com> - 2016-09-18 04:10 +0200
[tip:sched/core] stop_machine: Avoid a sleep and wakeup in stop_one_cpu() tip-bot for Cheng Chao <tipbot@zytor.com> - 2016-09-22 16:10 +0200
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