On Tue, 2025-10-14 at 11:04 +0100, Tvrtko Ursulin wrote:
>
> On 14/10/2025 09:52, Philipp Stanner wrote:
> > On Tue, 2025-10-14 at 08:26 +0100, Tvrtko Ursulin wrote:
> > >
> > > On 14/10/2025 07:53, Philipp Stanner wrote:
> > > > On Sat, 2025-10-11 at 15:19 +0100, Tvrtko Ursulin wrote:
> > > > >
> > > > > On 10/10/2025 11:49, Philipp Stanner wrote:
> > > > > > On Wed, 2025-10-08 at 09:53 +0100, Tvrtko Ursulin wrote:
> > > > > > > Move the code dealing with entities entering and exiting run
> > > > > > > queues to
> > > > > > > helpers to logically separate it from jobs entering and exiting
> > > > > > > entities.
> > > > > > >
> > > > > > > Signed-off-by: Tvrtko Ursulin <[email protected]>
> > > > > > > Cc: Christian König <[email protected]>
> > > > > > > Cc: Danilo Krummrich <[email protected]>
> > > > > > > Cc: Matthew Brost <[email protected]>
> > > > > > > Cc: Philipp Stanner <[email protected]>
> > > > > > > ---
> > > > > > > drivers/gpu/drm/scheduler/sched_entity.c | 64
> > > > > > > ++-------------
> > > > > > > drivers/gpu/drm/scheduler/sched_internal.h | 8 +-
> > > > > > > drivers/gpu/drm/scheduler/sched_main.c | 95
> > > > > > > +++++++++++++++++++---
> > > > > > > 3 files changed, 91 insertions(+), 76 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/gpu/drm/scheduler/sched_entity.c
> > > > > > > b/drivers/gpu/drm/scheduler/sched_entity.c
> > > > > > > index 4852006f2308..7a0a52ba87bf 100644
> > > > > > > --- a/drivers/gpu/drm/scheduler/sched_entity.c
> > > > > > > +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> > > > > > > @@ -456,24 +456,9 @@ drm_sched_job_dependency(struct
> > > > > > > drm_sched_job *job,
> > > > > > > return NULL;
> > > > > > > }
> > > > > > >
> > > > > > > -static ktime_t
> > > > > > > -drm_sched_rq_get_rr_ts(struct drm_sched_rq *rq, struct
> > > > > > > drm_sched_entity *entity)
> > > > > > > -{
> > > > > > > - ktime_t ts;
> > > > > > > -
> > > > > > > - lockdep_assert_held(&entity->lock);
> > > > > > > - lockdep_assert_held(&rq->lock);
> > > > > > > -
> > > > > > > - ts = ktime_add_ns(rq->rr_ts, 1);
> > > > > > > - entity->rr_ts = ts;
> > > > > > > - rq->rr_ts = ts;
> > > > > > > -
> > > > > > > - return ts;
> > > > > > > -}
> > > > > > > -
> > > > > > > struct drm_sched_job *drm_sched_entity_pop_job(struct
> > > > > > > drm_sched_entity *entity)
> > > > > > > {
> > > > > > > - struct drm_sched_job *sched_job, *next_job;
> > > > > > > + struct drm_sched_job *sched_job;
> > > > > >
> > > > > > `next_job` has been added in a previous job. Have you tried whether
> > > > > > patch-order can be reversed?
> > > > > >
> > > > > > Just asking; I don't want to cause unnecessary work here
> > > > >
> > > > > You are correct that there would be some knock on effect on a few
> > > > > other
> > > > > patches in the series but it is definitely doable. Because for certain
> > > > > argument can be made it would be logical to have it like that. Both
> > > > > this
> > > > > patch and "drm/sched: Move run queue related code into a separate
> > > > > file"
> > > > > would be then moved ahead of "drm/sched: Implement RR via FIFO". If
> > > > > you
> > > > > prefer it like that I can reshuffle no problem.
> > > >
> > > > I mean, it seems to make the overall git diff smaller, which is nice?
> > > >
> > > > If you don't see a significant reason against it, I'd say it's a good
> > > > idea.
> > >
> > > Okay deal. It isn't anything significant, just re-ordering patches with
> > > compile testing patches to ensure every step still builds.
>
> Completed locally.
>
> > > > > > >
> > > > > > > sched_job = drm_sched_entity_queue_peek(entity);
> > > > > > > if (!sched_job)
> > > > > > > @@ -502,26 +487,7 @@ struct drm_sched_job
> > > > > > > *drm_sched_entity_pop_job(struct drm_sched_entity *entity)
> > > > > > >
> > > > > > > spsc_queue_pop(&entity->job_queue);
> > > > > > >
> > > > > > > - /*
> > > > > > > - * Update the entity's location in the min heap according to
> > > > > > > - * the timestamp of the next job, if any.
> > > > > > > - */
> > > > > > > - next_job = drm_sched_entity_queue_peek(entity);
> > > > > > > - if (next_job) {
> > > > > > > - struct drm_sched_rq *rq;
> > > > > > > - ktime_t ts;
> > > > > > > -
> > > > > > > - spin_lock(&entity->lock);
> > > > > > > - rq = entity->rq;
> > > > > > > - spin_lock(&rq->lock);
> > > > > > > - if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
> > > > > > > - ts = next_job->submit_ts;
> > > > > > > - else
> > > > > > > - ts = drm_sched_rq_get_rr_ts(rq, entity);
> > > > > > > - drm_sched_rq_update_fifo_locked(entity, rq, ts);
> > > > > > > - spin_unlock(&rq->lock);
> > > > > > > - spin_unlock(&entity->lock);
> > > > > > > - }
> > > > > > > + drm_sched_rq_pop_entity(entity);
> > > > > > >
> > > > > > > /* Jobs and entities might have different lifecycles.
> > > > > > > Since we're
> > > > > > > * removing the job from the entities queue, set the
> > > > > > > jobs entity pointer
> > > > > > > @@ -611,30 +577,10 @@ void drm_sched_entity_push_job(struct
> > > > > > > drm_sched_job *sched_job)
> > > > > > > /* first job wakes up scheduler */
> > > > > > > if (first) {
> > > > > > > struct drm_gpu_scheduler *sched;
> > > > > > > - struct drm_sched_rq *rq;
> > > > > > >
> > > > > > > - /* Add the entity to the run queue */
> > > > > > > - spin_lock(&entity->lock);
> > > > > > > - if (entity->stopped) {
> > > > > > > - spin_unlock(&entity->lock);
> > > > > > > -
> > > > > > > - DRM_ERROR("Trying to push to a killed
> > > > > > > entity\n");
> > > > > > > - return;
> > > > > > > - }
> > > > > > > -
> > > > > > > - rq = entity->rq;
> > > > > > > - sched = rq->sched;
> > > > > > > -
> > > > > > > - spin_lock(&rq->lock);
> > > > > > > - drm_sched_rq_add_entity(rq, entity);
> > > > > > > - if (drm_sched_policy == DRM_SCHED_POLICY_RR)
> > > > > > > - submit_ts = entity->rr_ts;
> > > > > > > - drm_sched_rq_update_fifo_locked(entity, rq, submit_ts);
> > > > > > > -
> > > > > > > - spin_unlock(&rq->lock);
> > > > > > > - spin_unlock(&entity->lock);
> > > > > > > -
> > > > > > > - drm_sched_wakeup(sched);
> > > > > > > + sched = drm_sched_rq_add_entity(entity, submit_ts);
> > > > > > > + if (sched)
> > > > > > > + drm_sched_wakeup(sched);
> > > > > > > }
> > > > > > > }
> > > > > > > EXPORT_SYMBOL(drm_sched_entity_push_job);
> > > > > > > diff --git a/drivers/gpu/drm/scheduler/sched_internal.h
> > > > > > > b/drivers/gpu/drm/scheduler/sched_internal.h
> > > > > > > index 7ea5a6736f98..8269c5392a82 100644
> > > > > > > --- a/drivers/gpu/drm/scheduler/sched_internal.h
> > > > > > > +++ b/drivers/gpu/drm/scheduler/sched_internal.h
> > > > > > > @@ -12,13 +12,11 @@ extern int drm_sched_policy;
> > > > > > >
> > > > > > > void drm_sched_wakeup(struct drm_gpu_scheduler *sched);
> > > > > > >
> > > > > > > -void drm_sched_rq_add_entity(struct drm_sched_rq *rq,
> > > > > > > - struct drm_sched_entity *entity);
> > > > > > > +struct drm_gpu_scheduler *
> > > > > > > +drm_sched_rq_add_entity(struct drm_sched_entity *entity, ktime_t
> > > > > > > ts);
> > > > > > > void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
> > > > > > > struct drm_sched_entity
> > > > > > > *entity);
> > > > > > > -
> > > > > > > -void drm_sched_rq_update_fifo_locked(struct drm_sched_entity
> > > > > > > *entity,
> > > > > > > - struct drm_sched_rq *rq, ktime_t
> > > > > > > ts);
> > > > > > > +void drm_sched_rq_pop_entity(struct drm_sched_entity *entity);
> > > > > > >
> > > > > > > void drm_sched_entity_select_rq(struct drm_sched_entity
> > > > > > > *entity);
> > > > > > > struct drm_sched_job *drm_sched_entity_pop_job(struct
> > > > > > > drm_sched_entity *entity);
> > > > > > > diff --git a/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > > b/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > > index 8e62541b439a..e5d02c28665c 100644
> > > > > > > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > > > > > > @@ -151,9 +151,9 @@ static void
> > > > > > > drm_sched_rq_remove_fifo_locked(struct drm_sched_entity *entity,
> > > > > > > }
> > > > > > > }
> > > > > > >
> > > > > > > -void drm_sched_rq_update_fifo_locked(struct drm_sched_entity
> > > > > > > *entity,
> > > > > > > - struct drm_sched_rq *rq,
> > > > > > > - ktime_t ts)
> > > > > > > +static void drm_sched_rq_update_fifo_locked(struct
> > > > > > > drm_sched_entity *entity,
> > > > > > > + struct drm_sched_rq *rq,
> > > > > > > + ktime_t ts)
> > > > > > > {
> > > > > > > /*
> > > > > > > * Both locks need to be grabbed, one to protect from
> > > > > > > entity->rq change
> > > > > > > @@ -191,22 +191,45 @@ static void drm_sched_rq_init(struct
> > > > > > > drm_sched_rq *rq,
> > > > > > > /**
> > > > > > > * drm_sched_rq_add_entity - add an entity
> > > > > > > *
> > > > > > > - * @rq: scheduler run queue
> > > > > > > * @entity: scheduler entity
> > > > > > > + * @ts: submission timestamp
> > > > > > > *
> > > > > > > * Adds a scheduler entity to the run queue.
> > > > > > > + *
> > > > > > > + * Returns a DRM scheduler pre-selected to handle this entity.
> > > > > > > */
> > > > > > > -void drm_sched_rq_add_entity(struct drm_sched_rq *rq,
> > > > > > > - struct drm_sched_entity *entity)
> > > > > > > +struct drm_gpu_scheduler *
> > > > > > > +drm_sched_rq_add_entity(struct drm_sched_entity *entity, ktime_t
> > > > > > > ts)
> > > > > > > {
> > > > > >
> > > > > > I'm not sure if it's a good idea to have the scheduler returned from
> > > > > > that function. That doesn't make a whole lot of sense semantically.
> > > > > >
> > > > > > At the very least the function's docstring, maybe even its name,
> > > > > > should
> > > > > > be adjusted to detail why this makes sense. The commit message, too.
> > > > > > It's not trivially understood.
> > > > > >
> > > > > > I think I get why it's being done, but writing it down black on
> > > > > > white
> > > > > > gives us something to grasp.
> > > > > >
> > > > > > Sth like "adds an entity to a runqueue, selects to appropriate
> > > > > > scheduler and returns it for the purpose of XYZ"
> > > > >
> > > > > Yeah. Remeber your unlocked rq access slide and the discussion around
> > > > > it?
> > > >
> > > > Sure. Is that related, though? The slide was about many readers being
> > > > totally unlocked. The current drm_sched_entity_push_job() locks readers
> > > > correctly if I'm not mistaken.
> > > >
> > > > >
> > > > > Currently we have this:
> > > > >
> > > > > drm_sched_entity_push_job()
> > > > > {
> > > > > ...
> > > > > spin_lock(&entity->lock);
> > > > > ...
> > > > > rq = entity->rq;
> > > > > sched = rq->sched;
> > > > > ...
> > > > > spin_unlock(&rq->lock);
> > > > > spin_unlock(&entity->lock);
> > > > >
> > > > > drm_sched_wakeup(sched);
> > > > >
> > > > > Ie. we know entity->rq and rq->sched are guaranteed to be stable and
> > > > > present at this point because job is already in the queue and
> > > > > drm_sched_entity_select_rq() guarantees that.
> > > > >
> > > > > In this patch I moved all this block into drm_sched_rq_add_entity()
> > > > > but
> > > > > I wanted to leave drm_sched_wakeup() outside. Because I thought it is
> > > > > not the job of the run queue handling, and semantically the logic was
> > > > > "only once added to the entity we know the rq and scheduler for
> > > > > certain". That would open the door for future improvements and late
> > > > > rq/scheduler selection.
> > > > >
> > > > > But now I think it is premature and it would be better I simply move
> > > > > the
> > > > > wakekup inside drm_sched_rq_add_entity() together with all the rest.
> > > > >
> > > > > Does that sound like a plan for now?
> > > >
> > > > Hmmm. What I'm wondering most about if it really is a good idea to have
> > > > drm_sched_wakeup() in rq_add_entity().
> > > >
> > > > Do you think that makes semantically more sense than just reading:
> > > >
> > > > drm_sched_entity_push_job()
> > > > {
> > > > foo
> > > > bar
> > > > more_foo
> > > >
> > > > /* New job was added. Right time to wake up scheduler. */
> > > > drm_sched_wakeup();
> > >
> > > Problem here always is you need a sched pointer so question is simply
> > > how and where to get it.
> > >
> > > > I think both can make sense, but the above / current version seems to
> > > > make more sense to me.
> > >
> > > Current as in this patch or current as in the upstream codebase?
> > >
> > > In all cases the knowledge it is safe to use sched after unlocking is
> > > implicit.
> > >
> > > I see only two options:
> > >
> > > current)
> > >
> > > drm_sched_entity_push_job()
> > > {
> > > ...
> > > spin_unlock(&rq->lock);
> > > spin_unlock(&entity->lock);
> > >
> > > drm_sched_wakeup(sched);
> > >
> > > a)
> > >
> > > drm_sched_entity_push_job()
> > > {
> > > ...
> > > sched = drm_sched_rq_add_entity(entity, submit_ts);
> > > if (sched)
> > > drm_sched_wakeup(sched);
> > >
> > > b)
> > >
> > > drm_sched_rq_add_entity()
> > > {
> > > ...
> > > spin_unlock(&rq->lock);
> > > spin_unlock(&entity->lock);
> > >
> > > drm_sched_wakeup(sched);
> > >
> > >
> > > drm_sched_entity_push_job()
> > > {
> > > ...
> > > drm_sched_rq_add_entity(entity, submit_ts);
> > >
> > >
> > > b) is the same as today, a) perhaps a bit premature. Which do you prefer?
> >
> > Alright, I looked through everything now.
> >
> > The thing is just that I believe that it's a semantically confusing and
> > unclean concept of having drm_sched_rq_add_entity() return a scheduler
> > – except for when the entity is stopped. Then "there is no scheduler"
> > actually means "there is a scheduler, but that entity is stopped"
> >
> > In an ideal world:
> >
> > a) drm_sched_entity_push_job() wakes up the scheduler (as in your code,
> > and as in the current mainline code) and
> >
> > b) drm_sched_entity_push_job() is the one who checks whether the entity
> > is stopped. rq_add_entity() should just, well, add an entity to a
> > runqueue.
> >
> > Option b) then would need locks again and could race. So that's not so
> > cool.
> >
> > Possible solutions I can see is:
> >
> > 1. Have drm_sched_rq_add_entity() return an ERR_PTR instead of NULL.
>
> Maybe I am misunderstanding the idea, but what would be the benefit of
> this option?
>
> To clarify, I have:
>
> drm_sched_rq_add_entity()
> {
> ...
> if (entity->stopped) {
> ...
> return NULL;
>
> drm_sched_entity_push_job()
> {
> ...
> sched = drm_sched_rq_add_entity(entity);
> if (sched)
> drm_sched_wakeup(sched);
>
> And you propose:
>
> drm_sched_rq_add_entity()
> {
> ...
> if (entity->stopped) {
> ...
> return ERR_PTR(-ESOMETHING);
>
> drm_sched_entity_push_job()
> {
> ...
> sched = drm_sched_rq_add_entity(entity);
> if (!IS_ERR(sched))
> drm_sched_wakeup(sched);
>
>
> ?
Let's phrase it differently:
My issue is that
sched = func()
if (!sched) {
reads as "there is no scheduler". Whereas it should read as "there was
an error adding the entity".
How about this:
int drm_sched_entity_push_job(struct sched *scheddy)
{
if (stopped)
return -ENODEV; /* or other code, IDK */
*scheddy = XYZ;
…
ret = rq_add_entity(rq, entity, &sched)
if (ret == 0)
drm_sched_wakeup(sched);
Opinions? Matthew, Danilo, Christian?
:)
:(
P.
>
> > 2. Rename rq_add_entity()
>
> You mean to something signify it is also doing the wakeup? Or simply
> drm_sched_rq_add_first_entity()?
>
> > 3. Potentially leave it as is? I guess that doesn't work for your rq-
> > simplification?
>
> Leave drm_sched_wakeup in push job? Yeah that doesn't work for moving
> the rq handling into own helpers.
> > Option 1 would almost be my preference. What do you think?
>
> Lets see if I understand the option 1. I am fine with that one as
> described, and also with option 2.
>
> Regards,
>
> Tvrtko
