Re: [PATCH 4/9] sched: Clean up idle task SMP logic

Vincent Guittot
2014-01-21T17:27:35Z

On 21 January 2014 12:17, Peter Zijlstra <peterz@infradead.org> wrote:
> The idle post_schedule hook is just a vile waste of time, fix it proper.
>
> Cc: alex.shi@linaro.org
> Cc: mingo@kernel.org
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Tested-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> Link: http://lkml.kernel.org/r/20140117140939.GH11314@laptop.programming.kicks-ass.net
> ---
> kernel/sched/fair.c | 5 +++--
> kernel/sched/idle_task.c | 21 ++++++---------------
> 2 files changed, 9 insertions(+), 17 deletions(-)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2416,7 +2416,8 @@ void idle_exit_fair(struct rq *this_rq)
> update_rq_runnable_avg(this_rq, 0);
> }
>
> -#else
> +#else /* CONFIG_SMP */
> +
> static inline void update_entity_load_avg(struct sched_entity *se,
> int update_cfs_rq) {}
> static inline void update_rq_runnable_avg(struct rq *rq, int runnable) {}
> @@ -2428,7 +2429,7 @@ static inline void dequeue_entity_load_a
> int sleep) {}
> static inline void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq,
> int force_update) {}
> -#endif
> +#endif /* CONFIG_SMP */
>
> static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
> {
> --- a/kernel/sched/idle_task.c
> +++ b/kernel/sched/idle_task.c
> @@ -13,18 +13,8 @@ select_task_rq_idle(struct task_struct *
> {
> return task_cpu(p); /* IDLE tasks as never migrated */
> }
> -
> -static void pre_schedule_idle(struct rq *rq, struct task_struct *prev)
> -{
> - idle_exit_fair(rq);
> - rq_last_tick_reset(rq);
> -}
> -
> -static void post_schedule_idle(struct rq *rq)
> -{
> - idle_enter_fair(rq);
> -}
> #endif /* CONFIG_SMP */
> +
> /*
> * Idle tasks are unconditionally rescheduled:
> */
> @@ -37,8 +27,7 @@ static struct task_struct *pick_next_tas
> {
> schedstat_inc(rq, sched_goidle);
> #ifdef CONFIG_SMP
> - /* Trigger the post schedule to do an idle_enter for CFS */
> - rq->post_schedule = 1;
> + idle_enter_fair(rq);

If i have correctly followed the new function path that is introduced
by the patchset, idle_enter_fair is called after idle_balance whereas
it must be called before in order to update the
runnable_avg_sum/period of the rq before evaluating the interest of
pulling cfs task

Regards,
vincent

> #endif
> return rq->idle;
> }
> @@ -58,6 +47,10 @@ dequeue_task_idle(struct rq *rq, struct
>
> static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
> {
> +#ifdef CONFIG_SMP
> + idle_exit_fair(rq);
> + rq_last_tick_reset(rq);
> +#endif
> }
>
> static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
> @@ -101,8 +94,6 @@ const struct sched_class idle_sched_clas
>
> #ifdef CONFIG_SMP
> .select_task_rq = select_task_rq_idle,
> - .pre_schedule = pre_schedule_idle,
> - .post_schedule = post_schedule_idle,
> #endif
>
> .set_curr_task = set_curr_task_idle,
>
>