Re: [PATCH] sched: Optimize pick_next_task for idle_sched_class too
From: Pavan Kondeti
Date: Thu Feb 23 2017 - 05:34:38 EST
Hi Peter,
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 49ce1cb..51ca21e 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3321,15 +3321,14 @@ static inline void schedule_debug(struct task_struct *prev)
> static inline struct task_struct *
> pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> {
> - const struct sched_class *class = &fair_sched_class;
> + const struct sched_class *class;
> struct task_struct *p;
>
> /*
> * Optimization: we know that if all tasks are in
> * the fair class we can call that function directly:
> */
> - if (likely(prev->sched_class == class &&
> - rq->nr_running == rq->cfs.h_nr_running)) {
> + if (likely(rq->nr_running == rq->cfs.h_nr_running)) {
> p = fair_sched_class.pick_next_task(rq, prev, rf);
> if (unlikely(p == RETRY_TASK))
> goto again;
Would this delay pulling RT tasks from other CPUs? Lets say this CPU
has 2 fair tasks and 1 RT task. The RT task is sleeping now. Earlier,
we attempt to pull RT tasks from other CPUs in pick_next_task_rt(),
which is not done anymore.
Thanks,
Pavan
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