Re: [PATCH drm-misc-next v2] drm/sched: implement dynamic job-flow control
From: Luben Tuikov
Date: Fri Oct 13 2023 - 21:18:01 EST
On 2023-10-11 22:10, Danilo Krummrich wrote:
>
>
> 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@xxxxxxxxxx>
>>> ---
>>> 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/
This is still based on (an old version of) the Xe patches.
Please rebase your patch on top of a clean drm-misc-next, integrating my comments
in this thread (https://lore.kernel.org/r/b52c58e4-8ae6-4272-a67e-d811c6359127@xxxxxxx),
and post it for review.
I don't see much point in delaying this patch and it would most likely be okay
if you post it rebased off of a clean drm-misc-next (so I can apply it cleanly),
and you've integrated my comments in this thread.
--
Regards,
Luben
>>
>>>
>>> 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@xxxxxxx>, 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);
>>
>