Re: [PATCH 5/8] sched/eevdf: Reset lag when waking up on idle cpu

[Vincent Guittot]

On Mon, 21 Sept 2026 at 18:06, Kayra Cizmeci <kayracizmeci@xxxxxxxxx> wrote:
>
> Hi Vincent,
>
> > @@ -908,18 +908,25 @@ void decay_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> >       if (vlag <= 0)
> >               return;
> >
> > -     if (flags & ENQUEUE_MIGRATED)
> > -             return;
> > +     rq = rq_of(cfs_rq);
> >
> > -     /* Compute the sleep time */
> > -     delta_exec = rq_clock_task(rq_of(cfs_rq)) - se->exec_start;
> > -     if (unlikely(delta_exec <= 0))
> > -             return;
> > +     if (rq->curr == rq->idle) {
> > +             /* You can't claim any lag when waking on idle CPU */
> > +             vlag = 0;
> > +     } else if (!(flags & ENQUEUE_MIGRATED)) {
> > +             u64 now = rq_clock_task(rq);
> > +             s64 delta_exec;
> >
> > -     vlag -= calc_delta_fair(delta_exec, se);
> > +             /* Compute the sleep time */
> > +             delta_exec = now - se->exec_start;
> > +             if (unlikely(delta_exec <= 0))
> > +                     return;
> >
> > -     /* vlag can't become negative while sleeping */
> > -     se->vlag = max(0, vlag);
> > +             vlag -= calc_delta_fair(delta_exec, se);
> > +
> > +             /* vlag can't become neg while sleeping */
> > +             se->vlag = max(0, vlag);
> > +     }
> >  }
>
> When if (rq->curr == rq->idle) runs the else if does not. So on that branch
> we just set local vlag to 0. I think you wanted to set se->vlag to 0?

Argh, I messed up when cleaning the patch

yes it should be se->vlag = 0 for idle case

I re-ran tests, and the latency with hackbench decreased a bit

scheduling latency (us) for cyclictest and hackbench
                   tip/sched/core| this patchset
slice                 8ms / 16ms |  8ms  / 16 ms
99th Percentile               75 |    70 (  7 %)
99.9th Percentile            730 |   532 (+27 %)
Maximum                    15996 |  5290 (+67 %)

Thanks

>
>
> Thanks,
> Kayra :>