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@xxxxxxx>
>>> Tested-by: Li Yunxiang (Teddy) <Yunxiang.Li@xxxxxxx>
>>> ---
>>> 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,
