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SubjectRe: [PATCH] sched: next buddy hint on sleep and preempt path
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On Tue, 2011-03-01 at 21:43 -0800, Paul Turner wrote:
> On Tue, Mar 1, 2011 at 3:33 PM, Venkatesh Pallipadi <venki@google.com> wrote:

> > for_each_sched_entity(se) {
> > cfs_rq = cfs_rq_of(se);
> > dequeue_entity(cfs_rq, se, flags);
> >
> > /* Don't dequeue parent if it has other entities besides us */
> > - if (cfs_rq->load.weight)
> > + if (cfs_rq->load.weight) {
> > + /*
> > + * Bias pick_next to pick a task from this cfs_rq, as
> > + * p is sleeping when it is within its sched_slice.
> > + */
> > + if (task_flags & DEQUEUE_SLEEP && se->parent)
> > + set_next_buddy(se->parent);
>
> re-using the last_buddy would seem like a more natural fit here; also
> doesn't have a clobber race with a wakeup

Hm, that would break last_buddy no? A preempted task won't get the CPU
back after light preempting thread deactivates. (it's disabled atm
unless heavily overloaded anyway, but..)

This wants a tweak either way though.

static inline struct task_struct *task_of(struct sched_entity *se)
{
#ifdef CONFIG_SCHED_DEBUG
WARN_ON_ONCE(!entity_is_task(se));
#endif
return container_of(se, struct task_struct, se);
}

static void set_next_buddy(struct sched_entity *se)
{
if (likely(task_of(se)->policy != SCHED_IDLE)) {
for_each_sched_entity(se)
cfs_rq_of(se)->next = se;
}
}



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