lkml.org 
[lkml]   [2021]   [Oct]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] sched/core: forced idle accounting
On Mon, Oct 11, 2021 at 10:33 AM Hao Luo <haoluo@google.com> wrote:
>
> On Thu, Oct 7, 2021 at 5:08 PM Josh Don <joshdon@google.com> wrote:
> > -void sched_core_dequeue(struct rq *rq, struct task_struct *p)
> > +void sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags)
> > {
> > rq->core->core_task_seq++;
> >
> > - if (!sched_core_enqueued(p))
> > - return;
> > + if (sched_core_enqueued(p)) {
> > + rb_erase(&p->core_node, &rq->core_tree);
> > + RB_CLEAR_NODE(&p->core_node);
> > + }
> >
> > - rb_erase(&p->core_node, &rq->core_tree);
> > - RB_CLEAR_NODE(&p->core_node);
> > + /*
> > + * Migrating the last task off the cpu, with the cpu in forced idle
> > + * state. Reschedule to create an accounting edge for forced idle,
> > + * and re-examine whether the core is still in forced idle state.
> > + */
> > + if (!(flags & DEQUEUE_SAVE) && rq->nr_running == 1 &&
> > + rq->core->core_forceidle && rq->curr == rq->idle)
> > + resched_curr(rq);
>
> Resched_curr is probably an unwanted side effect of dequeue. Maybe we
> could extract the check and resched_curr out into a function, and call
> the function outside of sched_core_dequeue(). In that way, the
> interface of dequeue doesn't need to change.

This resched is an atypical case; normal load balancing won't steal
the last runnable task off a cpu. The main reasons this resched could
trigger are: migration due to affinity change, and migration due to
sched core doing a cookie_steal. Could bubble this up to
deactivate_task(), but seems less brittle to keep this in dequeue()
with the check against DEQUEUE_SAVE (since this creates an important
accounting edge). Thoughts?

> > /*
> > @@ -5765,7 +5782,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> > for_each_cpu_wrap(i, smt_mask, cpu) {
> > rq_i = cpu_rq(i);
> >
> > - if (i != cpu)
> > + if (i != cpu && (rq_i != rq->core || !core_clock_updated))
> > update_rq_clock(rq_i);
>
> Do you mean (rq_i != rq->core && !core_clock_updated)? I thought
> rq->core has core_clock updated always.

rq->clock is updated on entry to pick_next_task(). rq->core is only
updated if rq == rq->core, or if we've done the clock update for
rq->core above.

\
 
 \ /
  Last update: 2021-10-12 02:33    [W:0.106 / U:4.844 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site