Re: [PATCH v2 3/9] drm/sched: Add DRM_SCHED_POLICY_SINGLE_ENTITY scheduling policy

[Danilo Krummrich <dakr@xxxxxxxxxx>]

On 8/29/23 19:37, Danilo Krummrich wrote:
> On 8/11/23 04:31, Matthew Brost wrote:
> > DRM_SCHED_POLICY_SINGLE_ENTITY creates a 1 to 1 relationship between
> > scheduler and entity. No priorities or run queue used in this mode.
> > Intended for devices with firmware schedulers.
> >
> > v2:
> >    - Drop sched / rq union (Luben)
> >
> > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> > ---
> >   drivers/gpu/drm/scheduler/sched_entity.c | 69 ++++++++++++++++++------
> >   drivers/gpu/drm/scheduler/sched_fence.c  |  2 +-
> >   drivers/gpu/drm/scheduler/sched_main.c   | 63 +++++++++++++++++++---
> >   include/drm/gpu_scheduler.h              |  8 +++
> >   4 files changed, 119 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> > index 65a972b52eda..1dec97caaba3 100644
> > --- a/drivers/gpu/drm/scheduler/sched_entity.c
> > +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> > @@ -83,6 +83,7 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
> >       memset(entity, 0, sizeof(struct drm_sched_entity));
> >       INIT_LIST_HEAD(&entity->list);
> >       entity->rq = NULL;
> > +    entity->single_sched = NULL;
> >       entity->guilty = guilty;
> >       entity->num_sched_list = num_sched_list;
> >       entity->priority = priority;
> > @@ -90,8 +91,17 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
> >       RCU_INIT_POINTER(entity->last_scheduled, NULL);
> >       RB_CLEAR_NODE(&entity->rb_tree_node);
> > -    if(num_sched_list)
> > -        entity->rq = &sched_list[0]->sched_rq[entity->priority];
> > +    if (num_sched_list) {
> > +        if (sched_list[0]->sched_policy !=
> > +            DRM_SCHED_POLICY_SINGLE_ENTITY) {
> > +            entity->rq = &sched_list[0]->sched_rq[entity->priority];
> > +        } else {
> > +            if (num_sched_list != 1 || sched_list[0]->single_entity)
> > +                return -EINVAL;
> > +            sched_list[0]->single_entity = entity;
> > +            entity->single_sched = sched_list[0];
> > +        }
> > +    }
> >       init_completion(&entity->entity_idle);
> > @@ -124,7 +134,8 @@ void drm_sched_entity_modify_sched(struct drm_sched_entity *entity,
> >                       struct drm_gpu_scheduler **sched_list,
> >                       unsigned int num_sched_list)
> >   {
> > -    WARN_ON(!num_sched_list || !sched_list);
> > +    WARN_ON(!num_sched_list || !sched_list ||
> > +        !!entity->single_sched);
> >       entity->sched_list = sched_list;
> >       entity->num_sched_list = num_sched_list;
> > @@ -231,13 +242,15 @@ static void drm_sched_entity_kill(struct drm_sched_entity *entity)
> >   {
> >       struct drm_sched_job *job;
> >       struct dma_fence *prev;
> > +    bool single_entity = !!entity->single_sched;
> > -    if (!entity->rq)
> > +    if (!entity->rq && !single_entity)
> >           return;
> >       spin_lock(&entity->rq_lock);
> >       entity->stopped = true;
> > -    drm_sched_rq_remove_entity(entity->rq, entity);
> > +    if (!single_entity)
> > +        drm_sched_rq_remove_entity(entity->rq, entity);
>
> Looks like nothing prevents drm_sched_run_job_work() to fetch more jobs from the entity,
> hence if this is called for an entity still having queued up jobs and a still running
> scheduler, drm_sched_entity_kill() and drm_sched_run_job_work() would race for jobs, right?

I worked around this with:

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 9a5e9b7032da..0687da57757d 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -1025,7 +1025,8 @@ drm_sched_select_entity(struct drm_gpu_scheduler *sched, bool dequeue)
                return NULL;
 
        if (sched->single_entity) {
-               if (drm_sched_entity_is_ready(sched->single_entity))
+               if (drm_sched_entity_is_ready(sched->single_entity) &&
+                   !READ_ONCE(sched->single_entity->stopped))
                        return sched->single_entity;
 
                return NULL;

> Not sure if this is by intention because we don't expect the driver to drm_sched_entity_fini()
> as long as there are still queued up jobs. At least this is inconsistant to what
> drm_sched_entity_kill() does without DRM_SCHED_POLICY_SINGLE_ENTITY and should either be fixed
> or documented if we agree nothing else makes sense.
>
> I think it also touches my question on how to tear down the scheduler once a ring is removed
> or deinitialized.
>
> I know XE is going its own way in this respect, but I also feel like we're leaving drivers
> potentially being interested in DRM_SCHED_POLICY_SINGLE_ENTITY a bit alone on that. I think
> we should probably give drivers a bit more guidance on how to do that.
>
> Currently, I see two approaches.
>
> (1) Do what XE does, which means letting the scheduler run dry, which includes both the
>      entity's job queue and the schedulers pending_list. While jobs from the entity's queue
>      aren't pushing any more work to the ring on tear down, but just "flow through" to get
>      freed up eventually. (Hopefully I got that right.)
>
> (2) Kill the entity to cleanup jobs from the entity's queue, stop the scheduler and either
>      just wait for pending jobs or signal them right away and finally free them up.
>
> Actually there'd also be (3), which could be a mix of both, discard the entity's queued jobs,
> but let the pending_list run dry.
>
> I'm not saying we should provide a whole bunch of infrastructure for drivers, e.g. for (1)
> as you've mentioned already as well, there is probably not much to generalize anyway. However,
> I think we should document the options drivers have to tear things down and do enough to
> enable drivers using any option (as long as we agree it is reasonable).
>
> For Nouveau specifically, I'd probably like to go with (3).
>
> - Danilo
>
> >       spin_unlock(&entity->rq_lock);
> >       /* Make sure this entity is not used by the scheduler at the moment */
> > @@ -259,6 +272,20 @@ static void drm_sched_entity_kill(struct drm_sched_entity *entity)
> >       dma_fence_put(prev);
> >   }
> > +/**
> > + * drm_sched_entity_to_scheduler - Schedule entity to GPU scheduler
> > + * @entity: scheduler entity
> > + *
> > + * Returns GPU scheduler for the entity
> > + */
> > +struct drm_gpu_scheduler *
> > +drm_sched_entity_to_scheduler(struct drm_sched_entity *entity)
> > +{
> > +    bool single_entity = !!entity->single_sched;
> > +
> > +    return single_entity ? entity->single_sched : entity->rq->sched;
> > +}
> > +
> >   /**
> >    * drm_sched_entity_flush - Flush a context entity
> >    *
> > @@ -276,11 +303,12 @@ long drm_sched_entity_flush(struct drm_sched_entity *entity, long timeout)
> >       struct drm_gpu_scheduler *sched;
> >       struct task_struct *last_user;
> >       long ret = timeout;
> > +    bool single_entity = !!entity->single_sched;
> > -    if (!entity->rq)
> > +    if (!entity->rq && !single_entity)
> >           return 0;
> > -    sched = entity->rq->sched;
> > +    sched = drm_sched_entity_to_scheduler(entity);
> >       /**
> >        * The client will not queue more IBs during this fini, consume existing
> >        * queued IBs or discard them on SIGKILL
> > @@ -373,7 +401,7 @@ static void drm_sched_entity_wakeup(struct dma_fence *f,
> >           container_of(cb, struct drm_sched_entity, cb);
> >       drm_sched_entity_clear_dep(f, cb);
> > -    drm_sched_wakeup_if_can_queue(entity->rq->sched);
> > +    drm_sched_wakeup_if_can_queue(drm_sched_entity_to_scheduler(entity));
> >   }
> >   /**
> > @@ -387,6 +415,8 @@ static void drm_sched_entity_wakeup(struct dma_fence *f,
> >   void drm_sched_entity_set_priority(struct drm_sched_entity *entity,
> >                      enum drm_sched_priority priority)
> >   {
> > +    WARN_ON(!!entity->single_sched);
> > +
> >       spin_lock(&entity->rq_lock);
> >       entity->priority = priority;
> >       spin_unlock(&entity->rq_lock);
> > @@ -399,7 +429,7 @@ EXPORT_SYMBOL(drm_sched_entity_set_priority);
> >    */
> >   static bool drm_sched_entity_add_dependency_cb(struct drm_sched_entity *entity)
> >   {
> > -    struct drm_gpu_scheduler *sched = entity->rq->sched;
> > +    struct drm_gpu_scheduler *sched = drm_sched_entity_to_scheduler(entity);
> >       struct dma_fence *fence = entity->dependency;
> >       struct drm_sched_fence *s_fence;
> > @@ -501,7 +531,8 @@ struct drm_sched_job *drm_sched_entity_pop_job(struct drm_sched_entity *entity)
> >        * Update the entity's location in the min heap according to
> >        * the timestamp of the next job, if any.
> >        */
> > -    if (entity->rq->sched->sched_policy == DRM_SCHED_POLICY_FIFO) {
> > +    if (drm_sched_entity_to_scheduler(entity)->sched_policy ==
> > +        DRM_SCHED_POLICY_FIFO) {
> >           struct drm_sched_job *next;
> >           next = to_drm_sched_job(spsc_queue_peek(&entity->job_queue));
> > @@ -524,6 +555,8 @@ void drm_sched_entity_select_rq(struct drm_sched_entity *entity)
> >       struct drm_gpu_scheduler *sched;
> >       struct drm_sched_rq *rq;
> > +    WARN_ON(!!entity->single_sched);
> > +
> >       /* single possible engine and already selected */
> >       if (!entity->sched_list)
> >           return;
> > @@ -573,12 +606,13 @@ void drm_sched_entity_select_rq(struct drm_sched_entity *entity)
> >   void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
> >   {
> >       struct drm_sched_entity *entity = sched_job->entity;
> > -    bool first, fifo = entity->rq->sched->sched_policy ==
> > -        DRM_SCHED_POLICY_FIFO;
> > +    bool single_entity = !!entity->single_sched;
> > +    bool first;
> >       ktime_t submit_ts;
> >       trace_drm_sched_job(sched_job, entity);
> > -    atomic_inc(entity->rq->sched->score);
> > +    if (!single_entity)
> > +        atomic_inc(entity->rq->sched->score);
> >       WRITE_ONCE(entity->last_user, current->group_leader);
> >       /*
> > @@ -591,6 +625,10 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
> >       /* first job wakes up scheduler */
> >       if (first) {
> > +        struct drm_gpu_scheduler *sched =
> > +            drm_sched_entity_to_scheduler(entity);
> > +        bool fifo = sched->sched_policy == DRM_SCHED_POLICY_FIFO;
> > +
> >           /* Add the entity to the run queue */
> >           spin_lock(&entity->rq_lock);
> >           if (entity->stopped) {
> > @@ -600,13 +638,14 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
> >               return;
> >           }
> > -        drm_sched_rq_add_entity(entity->rq, entity);
> > +        if (!single_entity)
> > +            drm_sched_rq_add_entity(entity->rq, entity);
> >           spin_unlock(&entity->rq_lock);
> >           if (fifo)
> >               drm_sched_rq_update_fifo(entity, submit_ts);
> > -        drm_sched_wakeup_if_can_queue(entity->rq->sched);
> > +        drm_sched_wakeup_if_can_queue(sched);
> >       }
> >   }
> >   EXPORT_SYMBOL(drm_sched_entity_push_job);
> > diff --git a/drivers/gpu/drm/scheduler/sched_fence.c b/drivers/gpu/drm/scheduler/sched_fence.c
> > index 06cedfe4b486..f6b926f5e188 100644
> > --- a/drivers/gpu/drm/scheduler/sched_fence.c
> > +++ b/drivers/gpu/drm/scheduler/sched_fence.c
> > @@ -225,7 +225,7 @@ void drm_sched_fence_init(struct drm_sched_fence *fence,
> >   {
> >       unsigned seq;
> > -    fence->sched = entity->rq->sched;
> > +    fence->sched = drm_sched_entity_to_scheduler(entity);
> >       seq = atomic_inc_return(&entity->fence_seq);
> >       dma_fence_init(&fence->scheduled, &drm_sched_fence_ops_scheduled,
> >                  &fence->lock, entity->fence_context, seq);
> > diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> > index 545d5298c086..cede47afc800 100644
> > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > @@ -32,7 +32,8 @@
> >    * backend operations to the scheduler like submitting a job to hardware run queue,
> >    * returning the dependencies of a job etc.
> >    *
> > - * The organisation of the scheduler is the following:
> > + * The organisation of the scheduler is the following for scheduling policies
> > + * DRM_SCHED_POLICY_RR and DRM_SCHED_POLICY_FIFO:
> >    *
> >    * 1. Each hw run queue has one scheduler
> >    * 2. Each scheduler has multiple run queues with different priorities
> > @@ -43,6 +44,23 @@
> >    *
> >    * The jobs in a entity are always scheduled in the order that they were pushed.
> >    *
> > + * The organisation of the scheduler is the following for scheduling policy
> > + * DRM_SCHED_POLICY_SINGLE_ENTITY:
> > + *
> > + * 1. One to one relationship between scheduler and entity
> > + * 2. No priorities implemented per scheduler (single job queue)
> > + * 3. No run queues in scheduler rather jobs are directly dequeued from entity
> > + * 4. The entity maintains a queue of jobs that will be scheduled on the
> > + * hardware
> > + *
> > + * The jobs in a entity are always scheduled in the order that they were pushed
> > + * regardless of scheduling policy.
> > + *
> > + * A policy of DRM_SCHED_POLICY_RR or DRM_SCHED_POLICY_FIFO is expected to used
> > + * when the KMD is scheduling directly on the hardware while a scheduling policy
> > + * of DRM_SCHED_POLICY_SINGLE_ENTITY is expected to be used when there is a
> > + * firmware scheduler.
> > + *
> >    * Note that once a job was taken from the entities queue and pushed to the
> >    * hardware, i.e. the pending queue, the entity must not be referenced anymore
> >    * through the jobs entity pointer.
> > @@ -96,6 +114,8 @@ static inline void drm_sched_rq_remove_fifo_locked(struct drm_sched_entity *enti
> >   void drm_sched_rq_update_fifo(struct drm_sched_entity *entity, ktime_t ts)
> >   {
> > +    WARN_ON(!!entity->single_sched);
> > +
> >       /*
> >        * Both locks need to be grabbed, one to protect from entity->rq change
> >        * for entity from within concurrent drm_sched_entity_select_rq and the
> > @@ -126,6 +146,8 @@ void drm_sched_rq_update_fifo(struct drm_sched_entity *entity, ktime_t ts)
> >   static void drm_sched_rq_init(struct drm_gpu_scheduler *sched,
> >                     struct drm_sched_rq *rq)
> >   {
> > +    WARN_ON(sched->sched_policy == DRM_SCHED_POLICY_SINGLE_ENTITY);
> > +
> >       spin_lock_init(&rq->lock);
> >       INIT_LIST_HEAD(&rq->entities);
> >       rq->rb_tree_root = RB_ROOT_CACHED;
> > @@ -144,6 +166,8 @@ static void drm_sched_rq_init(struct drm_gpu_scheduler *sched,
> >   void drm_sched_rq_add_entity(struct drm_sched_rq *rq,
> >                    struct drm_sched_entity *entity)
> >   {
> > +    WARN_ON(!!entity->single_sched);
> > +
> >       if (!list_empty(&entity->list))
> >           return;
> > @@ -166,6 +190,8 @@ void drm_sched_rq_add_entity(struct drm_sched_rq *rq,
> >   void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
> >                   struct drm_sched_entity *entity)
> >   {
> > +    WARN_ON(!!entity->single_sched);
> > +
> >       if (list_empty(&entity->list))
> >           return;
> > @@ -641,7 +667,7 @@ int drm_sched_job_init(struct drm_sched_job *job,
> >                  struct drm_sched_entity *entity,
> >                  void *owner)
> >   {
> > -    if (!entity->rq)
> > +    if (!entity->rq && !entity->single_sched)
> >           return -ENOENT;
> >       job->entity = entity;
> > @@ -674,13 +700,16 @@ void drm_sched_job_arm(struct drm_sched_job *job)
> >   {
> >       struct drm_gpu_scheduler *sched;
> >       struct drm_sched_entity *entity = job->entity;
> > +    bool single_entity = !!entity->single_sched;
> >       BUG_ON(!entity);
> > -    drm_sched_entity_select_rq(entity);
> > -    sched = entity->rq->sched;
> > +    if (!single_entity)
> > +        drm_sched_entity_select_rq(entity);
> > +    sched = drm_sched_entity_to_scheduler(entity);
> >       job->sched = sched;
> > -    job->s_priority = entity->rq - sched->sched_rq;
> > +    if (!single_entity)
> > +        job->s_priority = entity->rq - sched->sched_rq;
> >       job->id = atomic64_inc_return(&sched->job_id_count);
> >       drm_sched_fence_init(job->s_fence, job->entity);
> > @@ -896,6 +925,13 @@ drm_sched_select_entity(struct drm_gpu_scheduler *sched)
> >       if (!drm_sched_can_queue(sched))
> >           return NULL;
> > +    if (sched->single_entity) {
> > +        if (drm_sched_entity_is_ready(sched->single_entity))
> > +            return sched->single_entity;
> > +
> > +        return NULL;
> > +    }
> > +
> >       /* Kernel run queue has higher priority than normal run queue*/
> >       for (i = DRM_SCHED_PRIORITY_COUNT - 1; i >= DRM_SCHED_PRIORITY_MIN; i--) {
> >           entity = sched->sched_policy == DRM_SCHED_POLICY_FIFO ?
> > @@ -1091,6 +1127,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
> >           return -EINVAL;
> >       sched->ops = ops;
> > +    sched->single_entity = NULL;
> >       sched->hw_submission_limit = hw_submission;
> >       sched->name = name;
> >       sched->submit_wq = submit_wq ? : system_wq;
> > @@ -1103,7 +1140,9 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
> >           sched->sched_policy = default_drm_sched_policy;
> >       else
> >           sched->sched_policy = sched_policy;
> > -    for (i = DRM_SCHED_PRIORITY_MIN; i < DRM_SCHED_PRIORITY_COUNT; i++)
> > +    for (i = DRM_SCHED_PRIORITY_MIN; sched_policy !=
> > +         DRM_SCHED_POLICY_SINGLE_ENTITY && i < DRM_SCHED_PRIORITY_COUNT;
> > +         i++)
> >           drm_sched_rq_init(sched, &sched->sched_rq[i]);
> >       init_waitqueue_head(&sched->job_scheduled);
> > @@ -1135,7 +1174,15 @@ void drm_sched_fini(struct drm_gpu_scheduler *sched)
> >       drm_sched_submit_stop(sched);
> > -    for (i = DRM_SCHED_PRIORITY_COUNT - 1; i >= DRM_SCHED_PRIORITY_MIN; i--) {
> > +    if (sched->single_entity) {
> > +        spin_lock(&sched->single_entity->rq_lock);
> > +        sched->single_entity->stopped = true;
> > +        spin_unlock(&sched->single_entity->rq_lock);
> > +    }
> > +
> > +    for (i = DRM_SCHED_PRIORITY_COUNT - 1; sched->sched_policy !=
> > +         DRM_SCHED_POLICY_SINGLE_ENTITY && i >= DRM_SCHED_PRIORITY_MIN;
> > +         i--) {
> >           struct drm_sched_rq *rq = &sched->sched_rq[i];
> >           spin_lock(&rq->lock);
> > @@ -1176,6 +1223,8 @@ void drm_sched_increase_karma(struct drm_sched_job *bad)
> >       struct drm_sched_entity *entity;
> >       struct drm_gpu_scheduler *sched = bad->sched;
> > +    WARN_ON(sched->sched_policy == DRM_SCHED_POLICY_SINGLE_ENTITY);
> > +
> >       /* don't change @bad's karma if it's from KERNEL RQ,
> >        * because sometimes GPU hang would cause kernel jobs (like VM updating jobs)
> >        * corrupt but keep in mind that kernel jobs always considered good.
> > diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> > index 897d52a4ff4f..04eec2d7635f 100644
> > --- a/include/drm/gpu_scheduler.h
> > +++ b/include/drm/gpu_scheduler.h
> > @@ -79,6 +79,7 @@ enum drm_sched_policy {
> >       DRM_SCHED_POLICY_DEFAULT,
> >       DRM_SCHED_POLICY_RR,
> >       DRM_SCHED_POLICY_FIFO,
> > +    DRM_SCHED_POLICY_SINGLE_ENTITY,
> >       DRM_SCHED_POLICY_COUNT,
> >   };
> > @@ -112,6 +113,9 @@ struct drm_sched_entity {
> >        */
> >       struct drm_sched_rq        *rq;
> > +    /** @single_sched: Single scheduler */
> > +    struct drm_gpu_scheduler    *single_sched;
> > +
> >       /**
> >        * @sched_list:
> >        *
> > @@ -473,6 +477,7 @@ struct drm_sched_backend_ops {
> >    * struct drm_gpu_scheduler - scheduler instance-specific data
> >    *
> >    * @ops: backend operations provided by the driver.
> > + * @single_entity: Single entity for the scheduler
> >    * @hw_submission_limit: the max size of the hardware queue.
> >    * @timeout: the time after which a job is removed from the scheduler.
> >    * @name: name of the ring for which this scheduler is being used.
> > @@ -503,6 +508,7 @@ struct drm_sched_backend_ops {
> >    */
> >   struct drm_gpu_scheduler {
> >       const struct drm_sched_backend_ops    *ops;
> > +    struct drm_sched_entity        *single_entity;
> >       uint32_t            hw_submission_limit;
> >       long                timeout;
> >       const char            *name;
> > @@ -585,6 +591,8 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
> >                 struct drm_gpu_scheduler **sched_list,
> >                 unsigned int num_sched_list,
> >                 atomic_t *guilty);
> > +struct drm_gpu_scheduler *
> > +drm_sched_entity_to_scheduler(struct drm_sched_entity *entity);
> >   long drm_sched_entity_flush(struct drm_sched_entity *entity, long timeout);
> >   void drm_sched_entity_fini(struct drm_sched_entity *entity);
> >   void drm_sched_entity_destroy(struct drm_sched_entity *entity);