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Date:   Thu, 12 Oct 2023 04:10:20 +0200
From:   Danilo Krummrich <dakr@...hat.com>
To:     Luben Tuikov <luben.tuikov@....com>, airlied@...il.com,
        daniel@...ll.ch, matthew.brost@...el.com,
        boris.brezillon@...labora.com, christian.koenig@....com,
        faith.ekstrand@...labora.com
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH drm-misc-next v2] drm/sched: implement dynamic job-flow
 control



On 10/12/23 03:52, Luben Tuikov wrote:
> Hi,
> 
> Thanks for fixing the title and submitting a v2 of this patch. Comments inlined below.
> 
> On 2023-10-09 18:35, Danilo Krummrich wrote:
>> Currently, job flow control is implemented simply by limiting the number
>> of jobs in flight. Therefore, a scheduler is initialized with a
>> submission limit that corresponds to the number of jobs which can be
>> sent to the hardware.
>>
>> This implies that for each job, drivers need to account for the maximum
>> job size possible in order to not overflow the ring buffer.
>>
>> However, there are drivers, such as Nouveau, where the job size has a
>> rather large range. For such drivers it can easily happen that job
>> submissions not even filling the ring by 1% can block subsequent
>> submissions, which, in the worst case, can lead to the ring run dry.
>>
>> In order to overcome this issue, allow for tracking the actual job size
>> instead of the number of jobs. Therefore, add a field to track a job's
>> submission credits, which represents the number of credits a job
>> contributes to the scheduler's submission limit.
>>
>> Signed-off-by: Danilo Krummrich <dakr@...hat.com>
>> ---
>> Changes in V2:
>> ==============
>>    - fixed up influence on scheduling fairness due to consideration of a job's
>>      size
>>      - If we reach a ready entity in drm_sched_select_entity() but can't actually
>>        queue a job from it due to size limitations, just give up and go to sleep
>>        until woken up due to a pending job finishing, rather than continue to try
>>        other entities.
>>    - added a callback to dynamically update a job's credits (Boris)
>>    - renamed 'units' to 'credits'
>>    - fixed commit message and comments as requested by Luben
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_job.c       |   2 +-
>>   drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c  |   2 +-
>>   drivers/gpu/drm/lima/lima_sched.c             |   2 +-
>>   drivers/gpu/drm/msm/msm_gem_submit.c          |   2 +-
>>   drivers/gpu/drm/nouveau/nouveau_sched.c       |   2 +-
>>   drivers/gpu/drm/panfrost/panfrost_drv.c       |   2 +-
>>   .../gpu/drm/scheduler/gpu_scheduler_trace.h   |   2 +-
>>   drivers/gpu/drm/scheduler/sched_entity.c      |   5 +-
>>   drivers/gpu/drm/scheduler/sched_main.c        | 101 +++++++++++++-----
>>   drivers/gpu/drm/v3d/v3d_gem.c                 |   2 +-
>>   include/drm/gpu_scheduler.h                   |  33 ++++--
>>   11 files changed, 115 insertions(+), 40 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
>> index 78476bc75b4e..d54daaf64bf1 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
>> @@ -115,7 +115,7 @@ int amdgpu_job_alloc(struct amdgpu_device *adev, struct amdgpu_vm *vm,
>>   	if (!entity)
>>   		return 0;
>>   
>> -	return drm_sched_job_init(&(*job)->base, entity, owner);
>> +	return drm_sched_job_init(&(*job)->base, entity, 1, owner);
>>   }
>>   
>>   int amdgpu_job_alloc_with_ib(struct amdgpu_device *adev,
>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c b/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
>> index 45403ea38906..74a446711207 100644
>> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
>> @@ -538,7 +538,7 @@ int etnaviv_ioctl_gem_submit(struct drm_device *dev, void *data,
>>   
>>   	ret = drm_sched_job_init(&submit->sched_job,
>>   				 &ctx->sched_entity[args->pipe],
>> -				 submit->ctx);
>> +				 1, submit->ctx);
>>   	if (ret)
>>   		goto err_submit_put;
>>   
>> diff --git a/drivers/gpu/drm/lima/lima_sched.c b/drivers/gpu/drm/lima/lima_sched.c
>> index 50c2075228aa..5dc6678e1eb9 100644
>> --- a/drivers/gpu/drm/lima/lima_sched.c
>> +++ b/drivers/gpu/drm/lima/lima_sched.c
>> @@ -123,7 +123,7 @@ int lima_sched_task_init(struct lima_sched_task *task,
>>   	for (i = 0; i < num_bos; i++)
>>   		drm_gem_object_get(&bos[i]->base.base);
>>   
>> -	err = drm_sched_job_init(&task->base, &context->base, vm);
>> +	err = drm_sched_job_init(&task->base, &context->base, 1, vm);
>>   	if (err) {
>>   		kfree(task->bos);
>>   		return err;
>> diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
>> index 3f1aa4de3b87..6d230c38e4f5 100644
>> --- a/drivers/gpu/drm/msm/msm_gem_submit.c
>> +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
>> @@ -48,7 +48,7 @@ static struct msm_gem_submit *submit_create(struct drm_device *dev,
>>   		return ERR_PTR(ret);
>>   	}
>>   
>> -	ret = drm_sched_job_init(&submit->base, queue->entity, queue);
>> +	ret = drm_sched_job_init(&submit->base, queue->entity, 1, queue);
>>   	if (ret) {
>>   		kfree(submit->hw_fence);
>>   		kfree(submit);
>> diff --git a/drivers/gpu/drm/nouveau/nouveau_sched.c b/drivers/gpu/drm/nouveau/nouveau_sched.c
>> index f26a814a9920..e991426d86e4 100644
>> --- a/drivers/gpu/drm/nouveau/nouveau_sched.c
>> +++ b/drivers/gpu/drm/nouveau/nouveau_sched.c
>> @@ -89,7 +89,7 @@ nouveau_job_init(struct nouveau_job *job,
>>   
>>   	}
>>   
>> -	ret = drm_sched_job_init(&job->base, &entity->base, NULL);
>> +	ret = drm_sched_job_init(&job->base, &entity->base, 1, NULL);
>>   	if (ret)
>>   		goto err_free_chains;
>>   
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
>> index b834777b409b..54d1c19bea84 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
>> @@ -274,7 +274,7 @@ static int panfrost_ioctl_submit(struct drm_device *dev, void *data,
>>   
>>   	ret = drm_sched_job_init(&job->base,
>>   				 &file_priv->sched_entity[slot],
>> -				 NULL);
>> +				 1, NULL);
>>   	if (ret)
>>   		goto out_put_job;
>>   
>> diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h b/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
>> index 3143ecaaff86..2e4ffdecc5dc 100644
>> --- a/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
>> +++ b/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
>> @@ -51,7 +51,7 @@ DECLARE_EVENT_CLASS(drm_sched_job,
>>   			   __assign_str(name, sched_job->sched->name);
>>   			   __entry->job_count = spsc_queue_count(&entity->job_queue);
>>   			   __entry->hw_job_count = atomic_read(
>> -				   &sched_job->sched->hw_rq_count);
>> +				   &sched_job->sched->submission_count);
>>   			   ),
>>   	    TP_printk("entity=%p, id=%llu, fence=%p, ring=%s, job count:%u, hw job count:%d",
>>   		      __entry->entity, __entry->id,
>> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
>> index 437c50867c99..6395090d5784 100644
>> --- a/drivers/gpu/drm/scheduler/sched_entity.c
>> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
>> @@ -401,7 +401,8 @@ 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(drm_sched_entity_to_scheduler(entity));
>> +	drm_sched_wakeup_if_can_queue(drm_sched_entity_to_scheduler(entity),
>> +				      entity);
>>   }
>>   
>>   /**
>> @@ -645,7 +646,7 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
>>   		if (fifo)
>>   			drm_sched_rq_update_fifo(entity, submit_ts);
>>   
>> -		drm_sched_wakeup_if_can_queue(sched);
>> +		drm_sched_wakeup_if_can_queue(sched, entity);
>>   	}
>>   }
>>   EXPORT_SYMBOL(drm_sched_entity_push_job);
>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
>> index 88ef8be2d3c7..da86dd0782d6 100644
>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>> @@ -93,6 +93,9 @@ int drm_sched_policy_default = DRM_SCHED_POLICY_FIFO;
>>   MODULE_PARM_DESC(sched_policy, "Specify the scheduling policy for entities on a run-queue, " __stringify(DRM_SCHED_POLICY_RR) " = Round Robin, " __stringify(DRM_SCHED_POLICY_FIFO) " = FIFO (default).");
>>   module_param_named(sched_policy, drm_sched_policy_default, int, 0444);
>>   
>> +static bool drm_sched_can_queue(struct drm_gpu_scheduler *sched,
>> +				struct drm_sched_entity *entity);
>> +
>>   static __always_inline bool drm_sched_entity_compare_before(struct rb_node *a,
>>   							    const struct rb_node *b)
>>   {
>> @@ -212,13 +215,15 @@ void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
>>   /**
>>    * drm_sched_rq_select_entity_rr - Select an entity which could provide a job to run
>>    *
>> + * @sched: the gpu scheduler
>>    * @rq: scheduler run queue to check.
>>    * @dequeue: dequeue selected entity
>>    *
>>    * Try to find a ready entity, returns NULL if none found.
>>    */
>>   static struct drm_sched_entity *
>> -drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq, bool dequeue)
>> +drm_sched_rq_select_entity_rr(struct drm_gpu_scheduler *sched,
>> +			      struct drm_sched_rq *rq, bool dequeue)
>>   {
>>   	struct drm_sched_entity *entity;
>>   
>> @@ -228,6 +233,12 @@ drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq, bool dequeue)
>>   	if (entity) {
>>   		list_for_each_entry_continue(entity, &rq->entities, list) {
>>   			if (drm_sched_entity_is_ready(entity)) {
>> +				/* If we can't queue yet, preserve the current
>> +				 * entity in terms of fairness.
>> +				 */
>> +				if (!drm_sched_can_queue(sched, entity))
>> +					goto out;
>> +
>>   				if (dequeue) {
>>   					rq->current_entity = entity;
>>   					reinit_completion(&entity->entity_idle);
>> @@ -239,8 +250,13 @@ drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq, bool dequeue)
>>   	}
>>   
>>   	list_for_each_entry(entity, &rq->entities, list) {
>> -
>>   		if (drm_sched_entity_is_ready(entity)) {
>> +			/* If we can't queue yet, preserve the current entity in
>> +			 * terms of fairness.
>> +			 */
>> +			if (!drm_sched_can_queue(sched, entity))
>> +				goto out;
>> +
>>   			if (dequeue) {
>>   				rq->current_entity = entity;
>>   				reinit_completion(&entity->entity_idle);
>> @@ -253,21 +269,23 @@ drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq, bool dequeue)
>>   			break;
>>   	}
>>   
>> +out:
>>   	spin_unlock(&rq->lock);
>> -
>>   	return NULL;
>>   }
>>   
>>   /**
>>    * drm_sched_rq_select_entity_fifo - Select an entity which provides a job to run
>>    *
>> + * @sched: the gpu scheduler
>>    * @rq: scheduler run queue to check.
>>    * @dequeue: dequeue selected entity
>>    *
>>    * 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, bool dequeue)
>> +drm_sched_rq_select_entity_fifo(struct drm_gpu_scheduler *sched,
>> +				struct drm_sched_rq *rq, bool dequeue)
>>   {
>>   	struct rb_node *rb;
>>   
>> @@ -277,6 +295,15 @@ drm_sched_rq_select_entity_fifo(struct drm_sched_rq *rq, bool dequeue)
>>   
>>   		entity = rb_entry(rb, struct drm_sched_entity, rb_tree_node);
>>   		if (drm_sched_entity_is_ready(entity)) {
>> +			/* If we can't queue yet, don't pick another entity
>> +			 * which's job might fit and wait until we got space for
>> +			 * this one in terms of fairness.
>> +			 */
>> +			if (!drm_sched_can_queue(sched, entity)) {
>> +				spin_unlock(&rq->lock);
>> +				return NULL;
>> +			}
>> +
> 
> I wonder if here it would've been cleaner to just do,
> 
> 			if (!drm_sched_can_queue(sched, entity)) {
> 				rb = NULL;
> 				break;
> 			}
> 
> in order to follow the natural flow of the R-B tree search?
> In other words, the loop invariant becomes false, we exit the loop,
> unlock and return NULL.
> 
> Yeah, let's do that.
> 
>>   			if (dequeue) {
>>   				rq->current_entity = entity;
>>   				reinit_completion(&entity->entity_idle);
>> @@ -302,13 +329,32 @@ static void drm_sched_run_job_queue(struct drm_gpu_scheduler *sched)
>>   /**
>>    * drm_sched_can_queue -- Can we queue more to the hardware?
>>    * @sched: scheduler instance
>> + * @entity: the scheduler entity
>>    *
>> - * Return true if we can push more jobs to the hw, otherwise false.
>> + * Return true if we can push at least one more job from @entity, false
>> + * otherwise.
>>    */
>> -static bool drm_sched_can_queue(struct drm_gpu_scheduler *sched)
>> +static bool drm_sched_can_queue(struct drm_gpu_scheduler *sched,
>> +				struct drm_sched_entity *entity)
>>   {
>> -	return atomic_read(&sched->hw_rq_count) <
>> -		sched->hw_submission_limit;
>> +	struct drm_sched_job *s_job;
>> +
>> +	s_job = to_drm_sched_job(spsc_queue_peek(&entity->job_queue));
>> +	if (!s_job)
>> +		return false;
>> +
>> +	if (sched->ops->update_job_credits) {
>> +		u32 credits = sched->ops->update_job_credits(s_job);
>> +
>> +		if (credits)
>> +			s_job->submission_credits = credits;
>> +	}
>> +
>> +	WARN_ON(s_job->submission_credits > sched->submission_limit);
>> +
>> +	return (sched->submission_limit -
>> +		atomic_read(&sched->submission_count)) >=
>> +		s_job->submission_credits;
>>   }
>>   
>>   /**
>> @@ -325,12 +371,10 @@ drm_sched_select_entity(struct drm_gpu_scheduler *sched, bool dequeue)
>>   	struct drm_sched_entity *entity;
>>   	int i;
>>   
>> -	if (!drm_sched_can_queue(sched))
>> -		return NULL;
>> -
>>   	if (sched->single_entity) {
>>   		if (!READ_ONCE(sched->single_entity->stopped) &&
>> -		    drm_sched_entity_is_ready(sched->single_entity))
>> +		    drm_sched_entity_is_ready(sched->single_entity) &&
>> +		    drm_sched_can_queue(sched, sched->single_entity))
>>   			return sched->single_entity;
> 
> This mixing of the Xe patches and this patch is very, very annoying.
> Here and in RR picking the entity mix-up with "dequeue" which is
> now "peek"...
> 
> I'd like to have applied this patch to drm-misc-next and inspect it further,
> but cannot chase around which version of the Xe patches this patch applies
> to, cleanly, so I'd really rather have had this patch on a clean drm-misc-next
> tree.

I pushed you a branch [1], it's based on drm-misc-next plus V4 of the sched changes for XE series.

I'll reply to the other comments tomorrow.

- Danilo

[1] https://gitlab.freedesktop.org/nouvelles/kernel/-/commits/sched-credits/
> 
>>   
>>   		return NULL;
>> @@ -339,9 +383,11 @@ drm_sched_select_entity(struct drm_gpu_scheduler *sched, bool dequeue)
>>   	/* 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 ?
>> -			drm_sched_rq_select_entity_fifo(&sched->sched_rq[i],
>> +			drm_sched_rq_select_entity_fifo(sched,
>> +							&sched->sched_rq[i],
>>   							dequeue) :
>> -			drm_sched_rq_select_entity_rr(&sched->sched_rq[i],
>> +			drm_sched_rq_select_entity_rr(sched,
>> +						      &sched->sched_rq[i],
>>   						      dequeue);
>>   		if (entity)
>>   			break;
>> @@ -399,7 +445,7 @@ static void drm_sched_job_done(struct drm_sched_job *s_job, int result)
>>   	struct drm_sched_fence *s_fence = s_job->s_fence;
>>   	struct drm_gpu_scheduler *sched = s_fence->sched;
>>   
>> -	atomic_dec(&sched->hw_rq_count);
>> +	atomic_sub(s_job->submission_credits, &sched->submission_count);
>>   	atomic_dec(sched->score);
>>   
>>   	trace_drm_sched_process_job(s_fence);
>> @@ -622,7 +668,8 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
>>   					      &s_job->cb)) {
>>   			dma_fence_put(s_job->s_fence->parent);
>>   			s_job->s_fence->parent = NULL;
>> -			atomic_dec(&sched->hw_rq_count);
>> +			atomic_sub(s_job->submission_credits,
>> +				   &sched->submission_count);
>>   		} else {
>>   			/*
>>   			 * remove job from pending_list.
>> @@ -683,7 +730,7 @@ void drm_sched_start(struct drm_gpu_scheduler *sched, bool full_recovery)
>>   	list_for_each_entry_safe(s_job, tmp, &sched->pending_list, list) {
>>   		struct dma_fence *fence = s_job->s_fence->parent;
>>   
>> -		atomic_inc(&sched->hw_rq_count);
>> +		atomic_add(s_job->submission_credits, &sched->submission_count);
>>   
>>   		if (!full_recovery)
>>   			continue;
>> @@ -764,6 +811,8 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs);
>>    * drm_sched_job_init - init a scheduler job
>>    * @job: scheduler job to init
>>    * @entity: scheduler entity to use
>> + * @submission_credits: the number of credits this job contributes to the
>> + * schdulers submission limit
> 
> Spelling: "schedulers"!
> 
> Please run your patch through scripts/checkpatch.pl --strict and inspect what it says.
> 
>>    * @owner: job owner for debugging
>>    *
>>    * Refer to drm_sched_entity_push_job() documentation
>> @@ -781,6 +830,7 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs);
>>    */
>>   int drm_sched_job_init(struct drm_sched_job *job,
>>   		       struct drm_sched_entity *entity,
>> +		       u32 submission_credits,
>>   		       void *owner)
>>   {
>>   	if (!entity->rq && !entity->single_sched)
>> @@ -792,6 +842,7 @@ int drm_sched_job_init(struct drm_sched_job *job,
>>   		return -ENOMEM;
>>   
>>   	INIT_LIST_HEAD(&job->list);
>> +	job->submission_credits = submission_credits ? submission_credits : 1;
>>   
>>   	xa_init_flags(&job->dependencies, XA_FLAGS_ALLOC);
>>   
>> @@ -1004,12 +1055,14 @@ EXPORT_SYMBOL(drm_sched_job_cleanup);
>>   /**
>>    * drm_sched_wakeup_if_can_queue - Wake up the scheduler
>>    * @sched: scheduler instance
>> + * @entity: the scheduler entity
>>    *
>>    * Wake up the scheduler if we can queue jobs.
>>    */
>> -void drm_sched_wakeup_if_can_queue(struct drm_gpu_scheduler *sched)
>> +void drm_sched_wakeup_if_can_queue(struct drm_gpu_scheduler *sched,
>> +				   struct drm_sched_entity *entity)
>>   {
>> -	if (drm_sched_can_queue(sched))
>> +	if (drm_sched_can_queue(sched, entity))
>>   		drm_sched_run_job_queue(sched);
>>   }
>>   
>> @@ -1147,7 +1200,7 @@ static void drm_sched_run_job_work(struct work_struct *w)
>>   
>>   	s_fence = sched_job->s_fence;
>>   
>> -	atomic_inc(&sched->hw_rq_count);
>> +	atomic_add(sched_job->submission_credits, &sched->submission_count);
>>   	drm_sched_job_begin(sched_job);
>>   
>>   	trace_drm_run_job(sched_job, entity);
>> @@ -1183,7 +1236,7 @@ static void drm_sched_run_job_work(struct work_struct *w)
>>    * @ops: backend operations for this scheduler
>>    * @submit_wq: workqueue to use for submission. If NULL, an ordered wq is
>>    *	       allocated and used
>> - * @hw_submission: number of hw submissions that can be in flight
>> + * @max_submission_credits: number of submission credits that can be in flight
> 
> Let's not use "in flight". Perhaps it is better to say,
> 
>   * @max_submission_credits: number of submission credits this scheduler can hold
>   *                          from all jobs,
> 
>>    * @hang_limit: number of times to allow a job to hang before dropping it
>>    * @timeout: timeout value in jiffies for the scheduler
>>    * @timeout_wq: workqueue to use for timeout work. If NULL, the system_wq is
>> @@ -1198,7 +1251,7 @@ static void drm_sched_run_job_work(struct work_struct *w)
>>   int drm_sched_init(struct drm_gpu_scheduler *sched,
>>   		   const struct drm_sched_backend_ops *ops,
>>   		   struct workqueue_struct *submit_wq,
>> -		   unsigned hw_submission, unsigned hang_limit,
>> +		   unsigned max_submission_credits, unsigned hang_limit,
>>   		   long timeout, struct workqueue_struct *timeout_wq,
>>   		   atomic_t *score, const char *name,
>>   		   enum drm_sched_policy sched_policy,
>> @@ -1211,7 +1264,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
>>   
>>   	sched->ops = ops;
>>   	sched->single_entity = NULL;
>> -	sched->hw_submission_limit = hw_submission;
>> +	sched->submission_limit = max_submission_credits;
>>   	sched->name = name;
>>   	if (!submit_wq) {
>>   		sched->submit_wq = alloc_ordered_workqueue(name, 0);
>> @@ -1238,7 +1291,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
>>   	init_waitqueue_head(&sched->job_scheduled);
>>   	INIT_LIST_HEAD(&sched->pending_list);
>>   	spin_lock_init(&sched->job_list_lock);
>> -	atomic_set(&sched->hw_rq_count, 0);
>> +	atomic_set(&sched->submission_count, 0);
>>   	INIT_DELAYED_WORK(&sched->work_tdr, drm_sched_job_timedout);
>>   	INIT_WORK(&sched->work_run_job, drm_sched_run_job_work);
>>   	INIT_WORK(&sched->work_free_job, drm_sched_free_job_work);
>> diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
>> index 2e94ce788c71..8479e5302f7b 100644
>> --- a/drivers/gpu/drm/v3d/v3d_gem.c
>> +++ b/drivers/gpu/drm/v3d/v3d_gem.c
>> @@ -417,7 +417,7 @@ v3d_job_init(struct v3d_dev *v3d, struct drm_file *file_priv,
>>   	job->free = free;
>>   
>>   	ret = drm_sched_job_init(&job->base, &v3d_priv->sched_entity[queue],
>> -				 v3d_priv);
>> +				 1, v3d_priv);
>>   	if (ret)
>>   		goto fail;
>>   
>> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
>> index 27f5778bbd6d..c4a53b259585 100644
>> --- a/include/drm/gpu_scheduler.h
>> +++ b/include/drm/gpu_scheduler.h
>> @@ -329,6 +329,8 @@ struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f);
>>    * @sched: the scheduler instance on which this job is scheduled.
>>    * @s_fence: contains the fences for the scheduling of job.
>>    * @finish_cb: the callback for the finished fence.
>> + * @submission_credits: the number of submission credits this job contributes to
>> + *                      the scheduler
>>    * @work: Helper to reschdeule job kill to different context.
>>    * @id: a unique id assigned to each job scheduled on the scheduler.
>>    * @karma: increment on every hang caused by this job. If this exceeds the hang
>> @@ -348,6 +350,8 @@ struct drm_sched_job {
>>   	struct drm_gpu_scheduler	*sched;
>>   	struct drm_sched_fence		*s_fence;
>>   
>> +	u32				submission_credits;
>> +
>>   	/*
>>   	 * work is used only after finish_cb has been used and will not be
>>   	 * accessed anymore.
>> @@ -471,6 +475,21 @@ struct drm_sched_backend_ops {
>>            * and it's time to clean it up.
>>   	 */
>>   	void (*free_job)(struct drm_sched_job *sched_job);
>> +
>> +	/**
>> +	 * @update_job_credits: Called once the scheduler is considering this
>> +	 * job for execution.
>> +	 *
>> +	 * Drivers may use this to update the job's submission credits, which is
>> +	 * useful to e.g. deduct the number of native fences which have been
>> +	 * signaled meanwhile.
>> +	 *
>> +	 * The callback must either return the new number of submission credits
>> +	 * for the given job, or zero if no update is required.
>> +	 *
>> +	 * This callback is optional.
>> +	 */
>> +	u32 (*update_job_credits)(struct drm_sched_job *sched_job);
>>   };
> 
> That's good.
> 
>>   
>>   /**
>> @@ -478,14 +497,14 @@ struct drm_sched_backend_ops {
>>    *
>>    * @ops: backend operations provided by the driver.
>>    * @single_entity: Single entity for the scheduler
>> - * @hw_submission_limit: the max size of the hardware queue.
>> + * @submission_limit: the maximim number of submission credits
>> + * @submission_count: the number of submission credits in flight
> 
> Is this clear enough?
> 
> I mean, what really is a "submission_limit"? What is it limiting really?
> Number of what? "Submissions"? No. It's credits.
> 
> ("Submission" seems to have become very popular, see
>   Message-ID: <a39eb381-4f2b-439b-b223-c5148167b225@....com>, maybe through Lore.)
> 
> So if "submission_credit_limit" and "submission_credit_count"
> seem too wordy, (and they kind of are), then perhaps use,
> 
> 	@credit_limit: the credit limit of this scheduler
> 	@credit_count: the current credit count of this scheduler
> 
> Also note the slight comment update for those two quantities.
> 
>>    * @timeout: the time after which a job is removed from the scheduler.
>>    * @name: name of the ring for which this scheduler is being used.
>>    * @sched_rq: priority wise array of run queues.
>>    * @job_scheduled: once @drm_sched_entity_do_release is called the scheduler
>>    *                 waits on this wait queue until all the scheduled jobs are
>>    *                 finished.
>> - * @hw_rq_count: the number of jobs currently in the hardware queue.
>>    * @job_id_count: used to assign unique id to the each job.
>>    * @submit_wq: workqueue used to queue @work_run_job and @work_free_job
>>    * @timeout_wq: workqueue used to queue @work_tdr
>> @@ -511,12 +530,12 @@ 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;
>> +	u32				submission_limit;
>> +	atomic_t			submission_count;
> 
> See above. Perhaps "credit_limit" and "credit_count".
> 
>>   	long				timeout;
>>   	const char			*name;
>>   	struct drm_sched_rq		sched_rq[DRM_SCHED_PRIORITY_COUNT];
>>   	wait_queue_head_t		job_scheduled;
>> -	atomic_t			hw_rq_count;
>>   	atomic64_t			job_id_count;
>>   	struct workqueue_struct		*submit_wq;
>>   	struct workqueue_struct		*timeout_wq;
>> @@ -539,7 +558,7 @@ struct drm_gpu_scheduler {
>>   int drm_sched_init(struct drm_gpu_scheduler *sched,
>>   		   const struct drm_sched_backend_ops *ops,
>>   		   struct workqueue_struct *submit_wq,
>> -		   uint32_t hw_submission, unsigned hang_limit,
>> +		   uint32_t max_submission_credits, unsigned hang_limit,
>>   		   long timeout, struct workqueue_struct *timeout_wq,
>>   		   atomic_t *score, const char *name,
>>   		   enum drm_sched_policy sched_policy,
>> @@ -548,6 +567,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
>>   void drm_sched_fini(struct drm_gpu_scheduler *sched);
>>   int drm_sched_job_init(struct drm_sched_job *job,
>>   		       struct drm_sched_entity *entity,
>> +		       u32 submission_credits,
>>   		       void *owner);
>>   void drm_sched_job_arm(struct drm_sched_job *job);
>>   int drm_sched_job_add_dependency(struct drm_sched_job *job,
>> @@ -570,7 +590,8 @@ void drm_sched_entity_modify_sched(struct drm_sched_entity *entity,
>>   
>>   void drm_sched_tdr_queue_imm(struct drm_gpu_scheduler *sched);
>>   void drm_sched_job_cleanup(struct drm_sched_job *job);
>> -void drm_sched_wakeup_if_can_queue(struct drm_gpu_scheduler *sched);
>> +void drm_sched_wakeup_if_can_queue(struct drm_gpu_scheduler *sched,
>> +				   struct drm_sched_entity *entity);
>>   bool drm_sched_submit_ready(struct drm_gpu_scheduler *sched);
>>   void drm_sched_submit_stop(struct drm_gpu_scheduler *sched);
>>   void drm_sched_submit_start(struct drm_gpu_scheduler *sched);
> 

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