Inlined:
On 2022-09-28 14:49, Andrey Grodzovsky wrote:
> When many entities are competing for the same run queue
> on the same scheduler, we observe an unusually long wait
> times and some jobs get starved. This has been observed on GPUVis.
>
> The issue is due to the Round Robin policy used by schedulers
> to pick up the next entity's job queue for execution. Under stress
> of many entities and long job queues within entity some
> jobs could be stuck for very long time in it's entity's
> queue before being popped from the queue and executed
> while for other entities with smaller job queues a job
> might execute earlier even though that job arrived later
> then the job in the long queue.
>
> Fix:
> Add FIFO selection policy to entities in run queue, chose next entity
> on run queue in such order that if job on one entity arrived
> earlier then job on another entity the first job will start
> executing earlier regardless of the length of the entity's job
> queue.
>
> v2:
> Switch to rb tree structure for entities based on TS of
> oldest job waiting in the job queue of an entity. Improves next
> entity extraction to O(1). Entity TS update
> O(log N) where N is the number of entities in the run-queue
>
> Drop default option in module control parameter.
>
> v3:
> Various cosmetical fixes and minor refactoring of fifo update function.
> (Luben)
"Cosmetic"
>
> v4:
> Switch drm_sched_rq_select_entity_fifo to in order search (Luben)
>
> v5: Fix up drm_sched_rq_select_entity_fifo loop
v5 is actually a major major update of the whole patch and working of the patch.
It fixes the entity selection from ready-first, timestamp-second, to
oldest-first
and ready-second, i.e. oldest-ready entity, as I suggested. The v5 blurb should
read:
v5: Fix drm_sched_rq_select_entity_fifo loop from reordering and timestamping on
every selection, and picking the last ready first, timestamp-second, to picking
the oldest-ready entity. No reinsertion. (Luben)
>
> Signed-off-by: Andrey Grodzovsky <andrey.grodzov...@amd.com>
> Tested-by: Li Yunxiang (Teddy) <yunxiang...@amd.com>
> ---
> drivers/gpu/drm/scheduler/sched_entity.c | 26 ++++++-
> drivers/gpu/drm/scheduler/sched_main.c | 99 +++++++++++++++++++++++-
> include/drm/gpu_scheduler.h | 32 ++++++++
> 3 files changed, 151 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c
> b/drivers/gpu/drm/scheduler/sched_entity.c
> index 6b25b2f4f5a3..f3ffce3c9304 100644
> --- a/drivers/gpu/drm/scheduler/sched_entity.c
> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> @@ -73,6 +73,7 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
> entity->priority = priority;
> entity->sched_list = num_sched_list > 1 ? sched_list : NULL;
> entity->last_scheduled = NULL;
> + RB_CLEAR_NODE(&entity->rb_tree_node);
>
> if(num_sched_list)
> entity->rq = &sched_list[0]->sched_rq[entity->priority];
> @@ -417,14 +418,16 @@ struct drm_sched_job *drm_sched_entity_pop_job(struct
> drm_sched_entity *entity)
>
> sched_job = to_drm_sched_job(spsc_queue_peek(&entity->job_queue));
> if (!sched_job)
> - return NULL;
> + goto skip;
>
> while ((entity->dependency =
> drm_sched_job_dependency(sched_job, entity))) {
> trace_drm_sched_job_wait_dep(sched_job, entity->dependency);
>
> - if (drm_sched_entity_add_dependency_cb(entity))
> - return NULL;
> + if (drm_sched_entity_add_dependency_cb(entity)) {
> + sched_job = NULL;
> + goto skip;
> + }
> }
>
> /* skip jobs from entity that marked guilty */
> @@ -443,6 +446,16 @@ struct drm_sched_job *drm_sched_entity_pop_job(struct
> drm_sched_entity *entity)
> smp_wmb();
>
> spsc_queue_pop(&entity->job_queue);
> +
> + /*
> + * It's when head job is extracted we can access the next job (or empty)
> + * queue and update the entity location in the min heap accordingly.
> + */
> +skip:
> + if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
> + drm_sched_rq_update_fifo(entity,
> + (sched_job ? sched_job->submit_ts :
> ktime_get()));
> +
> return sched_job;
> }
>
> @@ -502,11 +515,13 @@ void drm_sched_entity_push_job(struct drm_sched_job
> *sched_job)
> {
> struct drm_sched_entity *entity = sched_job->entity;
> bool first;
> + ktime_t ts = ktime_get();
>
> trace_drm_sched_job(sched_job, entity);
> atomic_inc(entity->rq->sched->score);
> WRITE_ONCE(entity->last_user, current->group_leader);
> first = spsc_queue_push(&entity->job_queue, &sched_job->queue_node);
> + sched_job->submit_ts = ts;
>
> /* first job wakes up scheduler */
> if (first) {
> @@ -518,8 +533,13 @@ void drm_sched_entity_push_job(struct drm_sched_job
> *sched_job)
> DRM_ERROR("Trying to push to a killed entity\n");
> return;
> }
> +
> drm_sched_rq_add_entity(entity->rq, entity);
> spin_unlock(&entity->rq_lock);
> +
> + if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
> + drm_sched_rq_update_fifo(entity, ts);
> +
> drm_sched_wakeup(entity->rq->sched);
> }
> }
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c
> b/drivers/gpu/drm/scheduler/sched_main.c
> index 4f2395d1a791..5349fc049384 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -62,6 +62,58 @@
> #define to_drm_sched_job(sched_job) \
> container_of((sched_job), struct drm_sched_job, queue_node)
>
> +int drm_sched_policy = DRM_SCHED_POLICY_RR;
> +
> +/**
> + * DOC: sched_policy (int)
> + * Used to override default entities scheduling policy in a run queue.
> + */
> +MODULE_PARM_DESC(sched_policy,
> + "specify schedule policy for entities on a runqueue
> (DRM_SCHED_POLICY_RR = Round Robin (default), DRM_SCHED_POLICY_FIFO = use
> FIFO");
> +module_param_named(sched_policy, drm_sched_policy, int, 0444);
> +
> +static __always_inline bool drm_sched_entity_compare_before(struct rb_node
> *a,
> + const struct
> rb_node *b)
> +{
> + struct drm_sched_entity *ent_a = rb_entry((a), struct
> drm_sched_entity, rb_tree_node);
> + struct drm_sched_entity *ent_b = rb_entry((b), struct
> drm_sched_entity, rb_tree_node);
> +
> + return ktime_before(ent_a->oldest_job_waiting,
> ent_b->oldest_job_waiting);
> +}
> +
> +static inline void drm_sched_rq_remove_fifo_locked(struct drm_sched_entity
> *entity)
> +{
> + struct drm_sched_rq *rq = entity->rq;
> +
> + if (!RB_EMPTY_NODE(&entity->rb_tree_node)) {
> + rb_erase_cached(&entity->rb_tree_node, &rq->rb_tree_root);
> + RB_CLEAR_NODE(&entity->rb_tree_node);
> + }
> +}
> +
> +void drm_sched_rq_update_fifo(struct drm_sched_entity *entity, ktime_t ts)
> +{
> + struct drm_sched_rq *rq;
> +
> + /*
> + * 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
> + * other to update the rb tree structure.
> + */
> + spin_lock(&entity->rq_lock);
> + spin_lock(&entity->rq->lock);
> +
> + rq = entity->rq;
> +
> + entity->oldest_job_waiting = ts;
> +
> + rb_add_cached(&entity->rb_tree_node, &rq->rb_tree_root,
> + drm_sched_entity_compare_before);
> +
> + spin_unlock(&entity->rq->lock);
> + spin_unlock(&entity->rq_lock);
> +}
> +
> /**
> * drm_sched_rq_init - initialize a given run queue struct
> *
> @@ -75,6 +127,7 @@ static void drm_sched_rq_init(struct drm_gpu_scheduler
> *sched,
> {
> spin_lock_init(&rq->lock);
> INIT_LIST_HEAD(&rq->entities);
> + rq->rb_tree_root = RB_ROOT_CACHED;
> rq->current_entity = NULL;
> rq->sched = sched;
> }
> @@ -92,9 +145,12 @@ void drm_sched_rq_add_entity(struct drm_sched_rq *rq,
> {
> if (!list_empty(&entity->list))
> return;
> +
> spin_lock(&rq->lock);
> +
> atomic_inc(rq->sched->score);
> list_add_tail(&entity->list, &rq->entities);
> +
> spin_unlock(&rq->lock);
> }
>
> @@ -111,23 +167,30 @@ void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
> {
> if (list_empty(&entity->list))
> return;
> +
> spin_lock(&rq->lock);
> +
> atomic_dec(rq->sched->score);
> list_del_init(&entity->list);
> +
> if (rq->current_entity == entity)
> rq->current_entity = NULL;
> +
> + if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
> + drm_sched_rq_remove_fifo_locked(entity);
> +
> spin_unlock(&rq->lock);
> }
>
> /**
> - * drm_sched_rq_select_entity - Select an entity which could provide a job
> to run
> + * drm_sched_rq_select_entity_rr - Select an entity which could provide a
> job to run
> *
> * @rq: scheduler run queue to check.
> *
> * Try to find a ready entity, returns NULL if none found.
> */
> static struct drm_sched_entity *
> -drm_sched_rq_select_entity(struct drm_sched_rq *rq)
> +drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq)
> {
> struct drm_sched_entity *entity;
>
> @@ -163,6 +226,34 @@ drm_sched_rq_select_entity(struct drm_sched_rq *rq)
> return NULL;
> }
>
> +/**
> + * drm_sched_rq_select_entity_fifo - Select an entity which provides a job
> to run
> + *
> + * @rq: scheduler run queue to check.
> + *
> + * Find oldest waiting ready entity, returns NULL if none found.
> + */
> +static struct drm_sched_entity *
> +drm_sched_rq_select_entity_fifo(struct drm_sched_rq *rq)
> +{
> + struct rb_node *rb;
> +
> + spin_lock(&rq->lock);
> + for (rb = rb_first_cached(&rq->rb_tree_root); rb; rb = rb_next(rb)) {
> + struct drm_sched_entity *entity;
> +
> + entity = rb_entry(rb, struct drm_sched_entity, rb_tree_node);
> + if (drm_sched_entity_is_ready(entity)) {
> + rq->current_entity = entity;
> + reinit_completion(&entity->entity_idle);
> + break;
> + }
> + }
> + spin_unlock(&rq->lock);
> +
> + return rb ? rb_entry(rb, struct drm_sched_entity, rb_tree_node) : NULL;
> +}
Yay!
With the changes to v5 blurb and testing this patch is:
Reviewed-by: Luben Tuikov <luben.tui...@amd.com>
Regards,
Luben
> +
> /**
> * drm_sched_job_done - complete a job
> * @s_job: pointer to the job which is done
> @@ -803,7 +894,9 @@ drm_sched_select_entity(struct drm_gpu_scheduler *sched)
>
> /* Kernel run queue has higher priority than normal run queue*/
> for (i = DRM_SCHED_PRIORITY_COUNT - 1; i >= DRM_SCHED_PRIORITY_MIN;
> i--) {
> - entity = drm_sched_rq_select_entity(&sched->sched_rq[i]);
> + entity = drm_sched_policy != DRM_SCHED_POLICY_FIFO ?
> +
> drm_sched_rq_select_entity_rr(&sched->sched_rq[i]) :
> +
> drm_sched_rq_select_entity_fifo(&sched->sched_rq[i]);
> if (entity)
> break;
> }
> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> index 599855c6a672..1f7d9dd1a444 100644
> --- a/include/drm/gpu_scheduler.h
> +++ b/include/drm/gpu_scheduler.h
> @@ -50,6 +50,12 @@ enum drm_sched_priority {
> DRM_SCHED_PRIORITY_UNSET = -2
> };
>
> +/* Used to chose between FIFO and RR jobs scheduling */
> +extern int drm_sched_policy;
> +
> +#define DRM_SCHED_POLICY_RR 0
> +#define DRM_SCHED_POLICY_FIFO 1
> +
> /**
> * struct drm_sched_entity - A wrapper around a job queue (typically
> * attached to the DRM file_priv).
> @@ -196,6 +202,21 @@ struct drm_sched_entity {
> * drm_sched_entity_fini().
> */
> struct completion entity_idle;
> +
> + /**
> + * @oldest_job_waiting:
> + *
> + * Marks earliest job waiting in SW queue
> + */
> + ktime_t oldest_job_waiting;
> +
> + /**
> + * @rb_tree_node:
> + *
> + * The node used to insert this entity into time based priority queue
> + */
> + struct rb_node rb_tree_node;
> +
> };
>
> /**
> @@ -205,6 +226,7 @@ struct drm_sched_entity {
> * @sched: the scheduler to which this rq belongs to.
> * @entities: list of the entities to be scheduled.
> * @current_entity: the entity which is to be scheduled.
> + * @rb_tree_root: root of time based priory queue of entities for FIFO
> scheduling
> *
> * Run queue is a set of entities scheduling command submissions for
> * one specific ring. It implements the scheduling policy that selects
> @@ -215,6 +237,7 @@ struct drm_sched_rq {
> struct drm_gpu_scheduler *sched;
> struct list_head entities;
> struct drm_sched_entity *current_entity;
> + struct rb_root_cached rb_tree_root;
> };
>
> /**
> @@ -314,6 +337,13 @@ struct drm_sched_job {
>
> /** @last_dependency: tracks @dependencies as they signal */
> unsigned long last_dependency;
> +
> + /**
> + * @submit_ts:
> + *
> + * When the job was pushed into the entity queue.
> + */
> + ktime_t submit_ts;
> };
>
> static inline bool drm_sched_invalidate_job(struct drm_sched_job *s_job,
> @@ -503,6 +533,8 @@ 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);
>
> +void drm_sched_rq_update_fifo(struct drm_sched_entity *entity, ktime_t ts);
> +
> int drm_sched_entity_init(struct drm_sched_entity *entity,
> enum drm_sched_priority priority,
> struct drm_gpu_scheduler **sched_list,
