Re: [PATCH] drm/scheduler: set current_entity to next when remove from rq

[Christian König]

Am 27.10.22 um 10:07 schrieb Luben Tuikov:
> On 2022-10-27 03:01, Luben Tuikov wrote:
> > On 2022-10-25 13:50, Luben Tuikov wrote:
> > > Looking...
> > >
> > > Regards,
> > > Luben
> > >
> > > On 2022-10-25 09:35, Alex Deucher wrote:
> > > > + Luben
> > > >
> > > > On Tue, Oct 25, 2022 at 2:55 AM brolerliew <brolerliew@xxxxxxxxx> wrote:
> > > > > When entity move from one rq to another, current_entity will be set to NULL
> > > > > if it is the moving entity. This make entities close to rq head got
> > > > > selected more frequently, especially when doing load balance between
> > > > > multiple drm_gpu_scheduler.
> > > > >
> > > > > Make current_entity to next when removing from rq.
> > > > >
> > > > > Signed-off-by: brolerliew <brolerliew@xxxxxxxxx>
> > > > > ---
> > > > >   drivers/gpu/drm/scheduler/sched_main.c | 5 +++--
> > > > >   1 file changed, 3 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> > > > > index 2fab218d7082..00b22cc50f08 100644
> > > > > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > > > > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > > > > @@ -168,10 +168,11 @@ void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
> > > > >          spin_lock(&rq->lock);
> > > > >
> > > > >          atomic_dec(rq->sched->score);
> > > > > -       list_del_init(&entity->list);
> > > > >
> > > > >          if (rq->current_entity == entity)
> > > > > -               rq->current_entity = NULL;
> > > > > +               rq->current_entity = list_next_entry(entity, list);
> > > > > +
> > > > > +       list_del_init(&entity->list);
> > > > >
> > > > >          if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
> > > > >                  drm_sched_rq_remove_fifo_locked(entity);
> > > > > --
> > > > > 2.34.1
> > Looks good. I'll pick it up into some other changes I've in tow, and repost
> > along with my changes, as they're somewhat related.
> Actually, the more I look at it, the more I think that we do want to set
> rq->current_entity to NULL in that function, in order to pick the next best entity
> (or scheduler for that matter), the next time around. See sched_entity.c,
> and drm_sched_rq_select_entity() where we start evaluating from the _next_
> entity.
>
> So, it is best to leave it to set it to NULL, for now.

Apart from that this patch here could cause a crash when the entity is 
the last one in the list.

In this case current current_entity would be set to an incorrect upcast 
of the head of the list.

Regards,
Christian.

> Regards,
> Luben