On 28 Mar 2023 11:26:37 +0200 Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> @@ -4878,22 +4878,55 @@ place_entity(struct cfs_rq *cfs_rq, stru
> if (WARN_ON_ONCE(!load))
> load = 1;
> lag = div_s64(lag, load);
> +
> + vruntime -= lag;
> + }
> +
> + /*
> + * Base the deadline on the 'normal' EEVDF placement policy in an
> + * attempt to not let the bonus crud below wreck things completely.
> + */
> + se->deadline = vruntime;
> +
> + /*
> + * The whole 'sleeper' bonus hack... :-/ This is strictly unfair.
> + *
> + * By giving a sleeping task a little boost, it becomes possible for a
> + * 50% task to compete equally with a 100% task. That is, strictly fair
> + * that setup would result in a 67% / 33% split. Sleeper bonus will
> + * change that to 50% / 50%.
> + *
> + * This thing hurts my brain, because tasks leaving with negative lag
> + * will move 'time' backward, so comparing against a historical
> + * se->vruntime is dodgy as heck.
> + */
> + if (sched_feat(PLACE_BONUS) &&
> + (flags & ENQUEUE_WAKEUP) && !(flags & ENQUEUE_MIGRATED)) {
> + /*
> + * If se->vruntime is ahead of vruntime, something dodgy
> + * happened and we cannot give bonus due to not having valid
> + * history.
> + */
> + if ((s64)(se->vruntime - vruntime) < 0) {
> + vruntime -= se->slice/2;
> + vruntime = max_vruntime(se->vruntime, vruntime);
> + }
> }
>
> - se->vruntime = vruntime - lag;
> + se->vruntime = vruntime;
>
> /*
> * When joining the competition; the exisiting tasks will be,
> * on average, halfway through their slice, as such start tasks
> * off with half a slice to ease into the competition.
> */
> - if (sched_feat(PLACE_DEADLINE_INITIAL) && initial)
> + if (sched_feat(PLACE_DEADLINE_INITIAL) && (flags & ENQUEUE_INITIAL))
> vslice /= 2;
>
> /*
> * EEVDF: vd_i = ve_i + r_i/w_i
> */
> - se->deadline = se->vruntime + vslice;
> + se->deadline += vslice;
> }
Because lag makes no sense for more-than-a-second sleepers, it is simpler to
make them able to preempt the current at the next tick, in line with what fork
can do at best.
