Re: [PATCH v2] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE
Date: Fri Sep 09 2016 - 04:19:33 EST
--in-reply-to doesn't work?
v1 is :
on 09/09/2016 04:13 PM, Cheng Chao wrote:
> For CONFIG_PREEMPT_NONE=y, when sched_exec() needs migration, sched_exec()
> calls stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg).
> 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.
> But in fact, all above works are almost useless(wasteful),the reason is
> migration_cpu_stop() can not migrate. why? migration_cpu_stop() needs the
> task is TASK_ON_RQ_QUEUED before it calls __migrate_task().
> This patch keeps the task TASK_RUNNING instead of TASK_UNINTERRUPTIBLE,
> so the migration_cpu_stop() can do useful works.
> Signed-off-by: Cheng Chao <chengchao@xxxxxxxxxxx>
> 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();
> return done.ret;