Re: [PATCH 1/1] sched/fair: Update min_vruntime in more relaxed way

[Yiwei Lin]

On 11/16/23 19:16, Abel Wu wrote:
> On 11/16/23 6:54 PM, Yiwei Lin Wrote:
> > As EEVDF adopts lag-based solution which is irrespective of
> > min_vruntime like CFS before, min_vruntime is only used as
> > an offset to avoid overflow on evaluation of avg_vruntime now.
> > Rely on the fact we will always update_curr() before change
> > to cfs_rq, it seems to make sense if we just
> > update_min_vruntime() with update_curr() to reduce the cost.
> >
> > Signed-off-by: Yiwei Lin <s921975628@xxxxxxxxx>
> > ---
> >   kernel/sched/fair.c | 20 +-------------------
> >   1 file changed, 1 insertion(+), 19 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 07f555857..5c40adfae 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3815,17 +3815,8 @@ static void reweight_entity(struct cfs_rq 
> > *cfs_rq, struct sched_entity *se,
> >       enqueue_load_avg(cfs_rq, se);
> >       if (se->on_rq) {
> >           update_load_add(&cfs_rq->load, se->load.weight);
> > -        if (!curr) {
> > -            /*
> > -             * The entity's vruntime has been adjusted, so let's check
> > -             * whether the rq-wide min_vruntime needs updated too. 
> > Since
> > -             * the calculations above require stable min_vruntime 
> > rather
> > -             * than up-to-date one, we do the update at the end of the
> > -             * reweight process.
> > -             */
> > +        if (!curr)
> >               __enqueue_entity(cfs_rq, se);
> > -            update_min_vruntime(cfs_rq);
> > -        }
> >       }
> >   }
> >   @@ -5347,15 +5338,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct 
> > sched_entity *se, int flags)
> >         update_cfs_group(se);
> >   -    /*
> > -     * Now advance min_vruntime if @se was the entity holding it back,
> > -     * except when: DEQUEUE_SAVE && !DEQUEUE_MOVE, in this case 
> > we'll be
> > -     * put back on, and if we advance min_vruntime, we'll be placed 
> > back
> > -     * further than we started -- ie. we'll be penalized.
> > -     */
> > -    if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) != DEQUEUE_SAVE)
> > -        update_min_vruntime(cfs_rq);
> > -
> >       if (cfs_rq->nr_running == 0)
> >           update_idle_cfs_rq_clock_pelt(cfs_rq);
> >   }
>
> For now, core pick of core scheduling relies on min_vruntime to be fresh,
> so please just fix commit eab03c23c2a1 to preserve its original behavior
> by moving update_min_vruntime() to proper position. And behavior change
> can be posted separated.

Sorry for not noticing the requirement on core scheduling and applying 
bad solution. I should take a closer look for the influence when 
changing the approach to update_min_vruntime().

I'll send another patch which just move update_min_vruntime() to the 
right place later on.

> BTW it seems unnecessary to include a cover-letter for a single patch.
Got it! Still learning how to work with the kernel mailing list. Thanks 
for the kind suggestion!
> Thanks,
>     Abel