Re: [PATCH 2/2][v3] sched: Extract the task putting code from pick_next_task()

From: Vincent Guittot
Date: Tue Apr 21 2020 - 10:53:21 EST


On Tue, 21 Apr 2020 at 12:50, Chen Yu <yu.c.chen@xxxxxxxxx> wrote:
>
> Introduce a new function put_prev_task_balance() to do the balance
> when necessary, and then put previous task back to the run queue.
> This function is extracted from pick_next_task() to prepare for
> future usage by other type of task picking logic.
>
> No functional change.
>
> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx>
> Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>

Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

> ---
> v3: According to Steven's suggestion, fix the comment
> to change put_next_task() to put_prev_task()
>
> Rename finish_prev_task() to put_prev_task_balance()
> as this reflects what we do before picking a new task.
>
> Per Valentin's suggestion, put the declaration of
> struct sched_class within the ifdef, given it isn't
> used outside of it.
> ---
> kernel/sched/core.c | 39 +++++++++++++++++++++++----------------
> 1 file changed, 23 insertions(+), 16 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3a61a3b8eaa9..c9d7880f6bf2 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3904,6 +3904,28 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt)
> schedstat_inc(this_rq()->sched_count);
> }
>
> +static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
> + struct rq_flags *rf)
> +{
> +#ifdef CONFIG_SMP
> + const struct sched_class *class;
> + /*
> + * We must do the balancing pass before put_prev_task(), such
> + * that when we release the rq->lock the task is in the same
> + * state as before we took rq->lock.
> + *
> + * We can terminate the balance pass as soon as we know there is
> + * a runnable task of @class priority or higher.
> + */
> + for_class_range(class, prev->sched_class, &idle_sched_class) {
> + if (class->balance(rq, prev, rf))
> + break;
> + }
> +#endif
> +
> + put_prev_task(rq, prev);
> +}
> +
> /*
> * Pick up the highest-prio task:
> */
> @@ -3937,22 +3959,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> }
>
> restart:
> -#ifdef CONFIG_SMP
> - /*
> - * We must do the balancing pass before put_next_task(), such
> - * that when we release the rq->lock the task is in the same
> - * state as before we took rq->lock.
> - *
> - * We can terminate the balance pass as soon as we know there is
> - * a runnable task of @class priority or higher.
> - */
> - for_class_range(class, prev->sched_class, &idle_sched_class) {
> - if (class->balance(rq, prev, rf))
> - break;
> - }
> -#endif
> -
> - put_prev_task(rq, prev);
> + put_prev_task_balance(rq, prev, rf);
>
> for_each_class(class) {
> p = class->pick_next_task(rq);
> --
> 2.17.1
>