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    SubjectRe: [PATCH 08/17] sched/fair: Implement an EEVDF like policy
    On Wed, Mar 29, 2023 at 1:12 AM Peter Zijlstra <peterz@infradead.org> wrote:
    >
    > On Tue, Mar 28, 2023 at 06:26:51PM -0700, Josh Don wrote:
    >
    > > > @@ -5088,19 +5307,20 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
    > > > static void
    > > > check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
    > > > {
    > > > - unsigned long ideal_runtime, delta_exec;
    > > > + unsigned long delta_exec;
    > > > struct sched_entity *se;
    > > > s64 delta;
    > > >
    > > > - /*
    > > > - * When many tasks blow up the sched_period; it is possible that
    > > > - * sched_slice() reports unusually large results (when many tasks are
    > > > - * very light for example). Therefore impose a maximum.
    > > > - */
    > > > - ideal_runtime = min_t(u64, sched_slice(cfs_rq, curr), sysctl_sched_latency);
    > > > + if (sched_feat(EEVDF)) {
    > > > + if (pick_eevdf(cfs_rq) != curr)
    > > > + goto preempt;
    > >
    > > This could shortcircuit the loop in pick_eevdf once we find a best
    > > that has less vruntime and sooner deadline than curr, since we know
    > > we'll never pick curr in that case. Might help performance when we
    > > have a large tree for this cfs_rq.
    >
    > Yeah, one of the things I did consider was having this set cfs_rq->next
    > such that the reschedule pick doesn't have to do the pick again. But I
    > figured keep things simple for now.

    Yea that makes sense. I was thinking something similar along the lines
    of cfs_rq->next as another way to avoid duplicate computation. But
    agreed this can be a future optimization.

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