Hi Peter,
On Thu, Feb 23, 2017 at 7:24 PM, Peter Zijlstra <pet...@infradead.org> wrote:
> On Thu, Feb 23, 2017 at 04:04:22PM +0530, Pavan Kondeti wrote:
>> 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.
>
> It should not; the two places of interrests are when we leave the RT
> class to run anything lower (fair,idle), at which point we'll pull,
> or when an RT tasks wakes up, at which point it'll push.
Can you kindly show me where we are pulling when a RT task goes to
sleep? Apart from class/prio change, I see pull happening only from
pick_next_task_rt().
Thanks,
Pavan
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