From: Cheng Chao <cs.os.kernel@gmail.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: mingo@kernel.org, peterz@infradead.org, tj@kernel.org,
akpm@linux-foundation.org, chris@chris-wilson.co.uk,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE
Date: Tue, 13 Sep 2016 10:45:27 +0800 [thread overview]
Message-ID: <1d49dc6f-50ca-7126-27ff-a60a6fb63ffe@gmail.com> (raw)
In-Reply-To: <20160912110307.GA2417@redhat.com>
on 09/12/2016 07:03 PM, Oleg Nesterov wrote:
> On 09/10, Cheng Chao wrote:
>>
>> @@ -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();
>> +#endif
>> wait_for_completion(&done.completion);
>> return done.ret;
>> }
>
> Cheng, I already tried twice to suggest to conditionalize this schedule,
> because it can only help if cpu == smp_processor_id, and you didn't reply.
> I still think _cond_resched() makes more sense.
>
> I won't really argue if you prefer it this way. But did you see my emails?
>
I read them, thanks. because Peter didn't receive my mails before, it took me much time
to fix my mailbox, so I didn't reply on time.
Ok, even if cpu != smp_processor_id(), to call schedule() instead _cond_resched() can
give the caller a chance not to sleep. when the caller runs on the cpu again, it may
likely find the completion is already done.
then the stopper thread cpu_stop_signal_done() and the caller wait_for_completion() will
actually run very soon.
I think it is trivial improvement. using cond_resched()/_cond_resched() is better for
readability, I choose the cond_resched().
thanks again.
> Oleg.
>
next prev parent reply other threads:[~2016-09-13 2:45 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <OF73BCE1E4.D2224FEC-ON48258025.0022CFA7-48258025.0022E3DC@kedacom.com>
2016-09-09 8:13 ` [PATCH v2] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Cheng Chao
2016-09-09 8:19 ` chengchao
2016-09-09 13:14 ` Oleg Nesterov
2016-09-09 16:24 ` Peter Zijlstra
2016-09-10 8:52 ` [PATCH v3] " Cheng Chao
2016-09-10 9:51 ` Cheng Chao
2016-09-10 16:33 ` Peter Zijlstra
2016-09-12 11:03 ` Oleg Nesterov
2016-09-13 2:45 ` Cheng Chao [this message]
2016-09-12 11:37 ` Peter Zijlstra
2016-09-12 11:41 ` Peter Zijlstra
2016-09-12 13:05 ` Oleg Nesterov
2016-09-12 15:01 ` Peter Zijlstra
2016-09-13 16:14 ` Oleg Nesterov
2016-09-13 16:37 ` Peter Zijlstra
2016-09-14 2:07 ` Cheng Chao
2016-09-14 7:50 ` Peter Zijlstra
2016-09-14 15:45 ` Oleg Nesterov
2016-09-22 13:59 ` [tip:sched/core] sched/core: Optimize __schedule() tip-bot for Peter Zijlstra
2016-09-13 4:03 ` [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Cheng Chao
2016-09-13 8:45 ` Peter Zijlstra
2016-09-14 2:01 ` [PATCH v4] stop_machine: Avoid a sleep and wakeup in the stop_one_cpu() Cheng Chao
2016-09-14 15:53 ` Oleg Nesterov
2016-09-18 2:07 ` Cheng Chao
2016-09-22 13:59 ` [tip:sched/core] stop_machine: Avoid a sleep and wakeup in stop_one_cpu() tip-bot for Cheng Chao
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