[PATCH v4] drm/sched: Add FIFO sched policy to run queue v3
Andrey Grodzovsky
andrey.grodzovsky at amd.com
Wed Sep 28 02:44:00 UTC 2022
Hey, i have problems with my git-send today so i just attached V5 as a
patch here.
Andrey
On 2022-09-27 19:56, Luben Tuikov wrote:
> Inlined:
>
> On 2022-09-22 12:15, Andrey Grodzovsky wrote:
>> On 2022-09-22 11:03, Luben Tuikov wrote:
>>> The title of this patch has "v3", but "v4" in the title prefix.
>>> If you're using "-v" to git-format-patch, please remove the "v3" from the title.
>>>
>>> Inlined:
>>>
>>> On 2022-09-21 14:28, Andrey Grodzovsky wrote:
>>>> When many entities competing for same run queue on
>>>> the same scheduler When many entities have unacceptably long wait
>>>> time for some jobs waiting stuck in the run queue before being picked
>>>> up are observed (seen using GPUVis).
>>> Use this as your opening:
>>>
>>> "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 stack for very long time in it's entity's
>>> "stuck", not "stack".
>>>
>>>> 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)
>>>>
>>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
>>>> Tested-by: Li Yunxiang (Teddy) <Yunxiang.Li at amd.com>
>>>> ---
>>>> drivers/gpu/drm/scheduler/sched_entity.c | 26 +++++-
>>>> drivers/gpu/drm/scheduler/sched_main.c | 107 ++++++++++++++++++++++-
>>>> include/drm/gpu_scheduler.h | 32 +++++++
>>>> 3 files changed, 159 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..565707a1c5c7 100644
>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>>> @@ -62,6 +62,64 @@
>>>> #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);
>>>> + }
>>>> +}
>>>> +
>>>> +static inline void drm_sched_rq_update_fifo_locked(struct drm_sched_entity *entity,
>>>> + ktime_t ts)
>>>> +{
>>>> + struct drm_sched_rq *rq = entity->rq;
>>>> +
>>>> + drm_sched_rq_remove_fifo_locked(entity);
>>>> +
>>>> + entity->oldest_job_waiting = ts;
>>>> +
>>>> + rb_add_cached(&entity->rb_tree_node, &rq->rb_tree_root,
>>>> + drm_sched_entity_compare_before);
>>>> +}
>>>> +
>>>> +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_update_fifo_locked(entity, ts);
>>>> +
>>>> + spin_unlock(&entity->rq->lock);
>>>> + spin_unlock(&entity->rq_lock);
>>>> +}
>>> I thought you were going to drop one of the locks here?
>>> Address this by either updating the comment to explain to future programmers
>>> what is going on here and why the locking is not consistent (2 vs 1 lock),
>>> or drop one of the locks, as per my previous review.
>>
>> Note that after last review drm_sched_rq_update_fifo_locked is not
>> called anywhere
>> besides drm_sched_rq_update_fifo and so becomes obsolete and I will
>> remove it now.
>> In this case the double locking above is consistent and the reason is
>> explained in the
>> comment above.
> WHen you say "it's consistent" you mean it's being done from other places, I suppose.
>
>
>>
>>>> +
>>>> /**
>>>> * drm_sched_rq_init - initialize a given run queue struct
>>>> *
>>>> @@ -75,6 +133,7 @@ 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 +151,12 @@ 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 +173,30 @@ 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 +232,36 @@ 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;
>>>> + bool found = false;
>>>> + struct drm_sched_entity *entity;
>>>> +
>>>> + spin_lock(&rq->lock);
>>>> + for (rb = rb_first_cached(&rq->rb_tree_root); rb; rb = rb_next(rb)) {
>>>> + 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);
>>>> + found = true;
>>>> + break;
>>>> + }
>>>> + }
>>>> + spin_unlock(&rq->lock);
>>>> +
>>>> + return found ? entity : NULL;
>>>> +}
>>> You really don't need "found", and you don't need "entity" to be outside the loop.
>>>
>>> As per my last review, use this (which I've compiled and run):
>>>
>>> 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;
>>> }
>>>
>>> The only way we can exit the loop is,
>>> 1. The loop invariant is false, i.e. rb == NULL, or
>>> 2. The "break;" jump from inside the if () inside the loop.
>>>
>>> Also note that "rb" does NOT need to be initialized, since, the for() statement
>>> is always executed, and the assignment "rb = rb_first_cached(&rq->rb_tree_root);"
>>> initializes it--this is why GCC doesn't complain :-)
>>>
>>> Also note that you don't need to export "entity" as it makes the for() loop relocatable
>>> to another function with only having a dependency on "rb" being defined--the loop
>>> is self-contained.
>>>
>>> At the "return" statement, we know that we've exited the loop, by either the loop
>>> invariant being false, i.e. rb == NULL, or by the "break;" jump, in which case
>>> we know that rb != NULL. This is why the "return;" statement as presented above works
>>> correctly.
>>>
>>> Please use that function in the way it is above, which is minimal and mature.
>>
>> Makes sense, missed the point that at the end rb will be set to NULL
> Yeah, use the loop as I've written it above.
>
> Okay, send out v5.
>
> Regards,
> Luben
>
>> Andrey
>>
>>
>>> Regards,
>>> Luben
>>>
>>>> +
>>>> /**
>>>> * drm_sched_job_done - complete a job
>>>> * @s_job: pointer to the job which is done
>>>> @@ -803,7 +902,9 @@ 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,
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