[PATCH v8] drm/sched: Add FIFO sched policy to run queue
Andrey Grodzovsky
andrey.grodzovsky at amd.com
Fri Sep 30 13:31:30 UTC 2022
Thanks for helping with review and good improvement ideas.
Pushed to drm-misc-next.
Andrey
On 2022-09-30 00:12, Luben Tuikov wrote:
> From: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
>
> 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)
>
> v4:
> Switch drm_sched_rq_select_entity_fifo to in order search (Luben)
>
> v5: Fix up drm_sched_rq_select_entity_fifo loop (Luben)
>
> v6: Add missing drm_sched_rq_remove_fifo_locked
>
> v7: Fix ts sampling bug and more cosmetic stuff (Luben)
>
> v8: Fix module parameter string (Luben)
>
> Cc: Luben Tuikov <luben.tuikov at amd.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Direct Rendering Infrastructure - Development <dri-devel at lists.freedesktop.org>
> Cc: AMD Graphics <amd-gfx at lists.freedesktop.org>
> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
> Tested-by: Yunxiang Li (Teddy) <Yunxiang.Li at amd.com>
> Signed-off-by: Luben Tuikov <luben.tuikov at amd.com>
> Reviewed-by: Luben Tuikov <luben.tuikov at amd.com>
> ---
> drivers/gpu/drm/scheduler/sched_entity.c | 20 +++++
> drivers/gpu/drm/scheduler/sched_main.c | 96 +++++++++++++++++++++++-
> include/drm/gpu_scheduler.h | 32 ++++++++
> 3 files changed, 145 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> index 6b25b2f4f5a308..7060e4ed5a3148 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];
> @@ -443,6 +444,19 @@ struct drm_sched_job *drm_sched_entity_pop_job(struct drm_sched_entity *entity)
> smp_wmb();
>
> 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.
> + */
> + if (drm_sched_policy == DRM_SCHED_POLICY_FIFO) {
> + struct drm_sched_job *next;
> +
> + next = to_drm_sched_job(spsc_queue_peek(&entity->job_queue));
> + if (next)
> + drm_sched_rq_update_fifo(entity, next->submit_ts);
> + }
> +
> return sched_job;
> }
>
> @@ -507,6 +521,7 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
> 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 = ktime_get();
>
> /* 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, sched_job->submit_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 4f2395d1a79182..ce86b03e838699 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -62,6 +62,55 @@
> #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, " __stringify(DRM_SCHED_POLICY_RR) " = Round Robin (default), " __stringify(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)
> +{
> + /*
> + * 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);
> +
> + drm_sched_rq_remove_fifo_locked(entity);
> +
> + entity->oldest_job_waiting = ts;
> +
> + rb_add_cached(&entity->rb_tree_node, &entity->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 +124,7 @@ 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 +142,12 @@ 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 +164,30 @@ 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 +223,34 @@ 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;
> +}
> +
> /**
> * drm_sched_job_done - complete a job
> * @s_job: pointer to the job which is done
> @@ -803,7 +891,9 @@ 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_fifo(&sched->sched_rq[i]) :
> + drm_sched_rq_select_entity_rr(&sched->sched_rq[i]);
> if (entity)
> break;
> }
> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> index 599855c6a6727b..1f7d9dd1a44484 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,
>
> base-commit: 2ab69739209c843a47af82c0620036b233c83688
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