Messages in this thread | | | Date | Fri, 17 Jan 2014 15:26:44 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 4/4] sched: Idle task shortcut optimization |
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On Fri, Jan 17, 2014 at 10:04:04AM +0100, Daniel Lezcano wrote: > @@ -2679,11 +2715,8 @@ need_resched: > > pre_schedule(rq, prev); > > - if (unlikely(!rq->nr_running)) > - rq->idle_stamp = idle_balance(rq) ? 0 : rq_clock(rq); > - > put_prev_task(rq, prev); > - next = pick_next_task(rq); > + next = pick_next_task_or_idle(rq); > clear_tsk_need_resched(prev); > clear_preempt_need_resched(); > rq->skip_clock_update = 0;
I have vague memories that we need to have idle_balance() before put_prev_task(), but I can't recollect why this would be so.
That said, if I resurrect these patches:
https://lkml.org/lkml/2012/6/14/271
I suppose we could write something like:
struct task_struct *pick_next_task(struct rq *rq, struct task_struct *prev) { const struct sched_class *class; struct task_struct *p;
again: if (likely(rq->nr_running)) {
if (likely(rq->nr_running == rq->cfs.h_nr_running)) return fair_sched_class.pick_next_task(rq, prev);
for_each_class(class) { p = class->pick_next_task(rq, prev); if (p) return p; } }
if (idle_balance(rq)) goto again;
rq->idle_stamp = rq_clock(rq);
return idle_sched_class.pick_next_task(rq, prev); }
Which keeps idle_balance() before put_prev_task(), and by using idle_sched_clas.pick_next_task() doesn't rape the idle class interface like you did :-)
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