Re: [PATCH drm-misc-next v3] drm/sched: implement dynamic job-flow control
From: Luben Tuikov
Date: Thu Oct 26 2023 - 21:14:30 EST
On 2023-10-26 17:13, Luben Tuikov wrote:
> On 2023-10-26 12:13, 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 credit
>> 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
>> credit count, which represents the number of credits a job contributes
>> to the scheduler's credit 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
>>
>> Changes in V3:
>> ==============
>> - rebased onto V7 of the "DRM scheduler changes for Xe" series by Matt
>> - move up drm_sched_can_queue() instead of adding a forward declaration
>> (Boris)
>> - add a drm_sched_available_credits() helper (Boris)
>> - adjust control flow in drm_sched_rq_select_entity_fifo() to Luben's proposal
>> - re-phrase a few comments and fix a typo (Luben)
>> - change naming of all structures credit fields and function parameters to the
>> following scheme
>> - drm_sched_job::credits
>> - drm_gpu_scheduler::credit_limit
>> - drm_gpu_scheduler::credit_count
>> - drm_sched_init(..., u32 credit_limit, ...)
>> - drm_sched_job_init(..., u32 credits, ...)
>> - add proper documentation for the scheduler's job-flow control mechanism
>>
>> This patch is based on V7 of the "DRM scheduler changes for Xe" series. [1]
>> provides a branch based on drm-misc-next, with the named series and this patch
>> on top of it.
>>
>> [1] https://gitlab.freedesktop.org/nouvelles/kernel/-/commits/sched-credits/
>> ---
>> Documentation/gpu/drm-mm.rst | 6 +
>> 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 | 4 +-
>> drivers/gpu/drm/scheduler/sched_main.c | 142 ++++++++++++++----
>> drivers/gpu/drm/v3d/v3d_gem.c | 2 +-
>> include/drm/gpu_scheduler.h | 33 +++-
>> 12 files changed, 152 insertions(+), 49 deletions(-)
>>
>> diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst
>> index 602010cb6894..acc5901ac840 100644
>> --- a/Documentation/gpu/drm-mm.rst
>> +++ b/Documentation/gpu/drm-mm.rst
>> @@ -552,6 +552,12 @@ Overview
>> .. kernel-doc:: drivers/gpu/drm/scheduler/sched_main.c
>> :doc: Overview
>>
>> +Flow Control
>> +------------
>> +
>> +.. kernel-doc:: drivers/gpu/drm/scheduler/sched_main.c
>> + :doc: Flow Control
>> +
>> Scheduler Function References
>> -----------------------------
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_job.c
>> index 1f357198533f..62bb7fc7448a 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 2416c526f9b0..3d0f8d182506 100644
>> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem_submit.c
>> @@ -535,7 +535,7 @@ 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 23a6276f1332..cdcb37ff62c3 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 99744de6c05a..c002cabe7b9c 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 7e64b5ef90fb..1b2cc3f2e1c7 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..f8ed093b7356 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->credit_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 409e4256f6e7..b79e0672b94f 100644
>> --- a/drivers/gpu/drm/scheduler/sched_entity.c
>> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
>> @@ -370,7 +370,7 @@ 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(entity->rq->sched);
>> + drm_sched_wakeup_if_can_queue(entity->rq->sched, entity);
>> }
>>
>> /**
>> @@ -602,7 +602,7 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
>> if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
>> drm_sched_rq_update_fifo(entity, submit_ts);
>>
>> - drm_sched_wakeup_if_can_queue(entity->rq->sched);
>> + drm_sched_wakeup_if_can_queue(entity->rq->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 246213963928..3cc3dc0091fc 100644
>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>> @@ -48,6 +48,30 @@
>> * through the jobs entity pointer.
>> */
>>
>> +/**
>> + * DOC: Flow Control
>> + *
>> + * The DRM GPU scheduler provides a flow control mechanism to regulate the rate
>> + * in which the jobs fetched from scheduler entities are executed.
>> + *
>> + * In this context the &drm_gpu_scheduler keeps track of a driver specified
>> + * credit limit representing the capacity of this scheduler and a credit count;
>> + * every &drm_sched_job carries a driver specified number of credits.
>> + *
>> + * Once a job is executed (but not yet finished), the job's credits contribute
>> + * to the scheduler's credit count until the job is finished. If by executing
>> + * one more job the scheduler's credit count would exceed the scheduler's
>> + * credit limit, the job won't be executed. Instead, the scheduler will wait
>> + * until the credit count has decreased enough to not overflow its credit limit.
>> + * This implies waiting for previously executed jobs.
>> + *
>> + * Optionally, drivers can register a callback (update_job_credits) provided by
>
> "can" --> "may".
>
>> + * struct drm_sched_backend_ops to update the job's credits dynamically. The
>> + * scheduler will execute this callback every time the scheduler considers a job
>
> No future tense, "will execute" --> "executes", because when this patch lands,
> it all becomes present reality. See below for a reworded paragraph.
>
>> + * for execution and subsequently checks whether the job fits the scheduler's
>> + * credit limit.
>
> This here is a good explanation of what update_job_credits() does, but the one
> where this callback is defined in the scheduler ops is not very clear (see further down
> into the patch).
>
> I think we shouldn't use the word "update" as we don't really have any "update" code,
> a la,
> if old value != new value, then
> old value = new value # update it
> in the code using this new sched op.
>
> Perhaps it should be a "get_job_credits()" as this is how this function is used
> in drm_sched_can_queue().
>
> Perhaps this adds some clarity:
>
> * Optionally, drivers may register a sched ops callback, get_job_credits(), which
> * returns the number of credits the job passed as an argument would take when
> * submitted to driver/hardware. The scheduler executes this callback every time it
> * considers a job for execution in order to check if the job's credits fit
> * into the scheduler's credit limit.
>
> (FWIW, it may be doing some "update" into the driver/firmware/hardware, but DRM
> has no visibility or care for that, since DRM is using it simply as "tell me
> the number or credits this job would take.")
>
>> + */
>> +
>> #include <linux/wait.h>
>> #include <linux/sched.h>
>> #include <linux/completion.h>
>> @@ -75,6 +99,46 @@ int drm_sched_policy = 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, int, 0444);
>>
>> +static u32 drm_sched_available_credits(struct drm_gpu_scheduler *sched)
>> +{
>> + u32 credits;
>> +
>> + WARN_ON(check_sub_overflow(sched->credit_limit,
>> + atomic_read(&sched->credit_count),
>> + &credits));
>> +
>> + return credits;
>> +}
>> +
>> +/**
>> + * drm_sched_can_queue -- Can we queue more to the hardware?
>> + * @sched: scheduler instance
>> + * @entity: the scheduler entity
>> + *
>> + * 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,
>> + struct drm_sched_entity *entity)
>> +{
>> + struct drm_sched_job *s_job;
>> +
>> + s_job = to_drm_sched_job(spsc_queue_peek(&entity->job_queue));
>> + if (!s_job)
>> + return false;
>
> We don't have this gating logic at the moment, and I don't think
> we need it.
>
> At the current state of the code, we don't care if there's jobs
> in the incoming queue or not.
>
> The only thing we should check here for is the credit availability
> for _this job_, as you do in the code below.
I see it now--never mind.
(I would've probably added a comment--something like
/* Incoming queue empty--nothing to schedule, return false. */
as it circles all the way back to where we pick the next job to schedule.)
So, I ported this patch to drm-misc-next and then to 6.6-rc7 and ran
with it. All is good.
I think this patch is ready to go in after addressing the cosmetic fixes
to comments and clarity--if you also feel the same way.
Thanks! Great job!
Regards,
Luben
>
>> +
>> + if (sched->ops->update_job_credits) {
>> + u32 credits = sched->ops->update_job_credits(s_job);
>> +
>> + if (credits)
>> + s_job->credits = credits;
>> + }
>> +
>> + WARN_ON(s_job->credits > sched->credit_limit);
>> +
>> + return drm_sched_available_credits(sched) >= s_job->credits;
>> +}
>> +
>> static __always_inline bool drm_sched_entity_compare_before(struct rb_node *a,
>> const struct rb_node *b)
>> {
>> @@ -186,12 +250,14 @@ 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.
>> *
>> * 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)
>> +drm_sched_rq_select_entity_rr(struct drm_gpu_scheduler *sched,
>> + struct drm_sched_rq *rq)
>> {
>> struct drm_sched_entity *entity;
>>
>> @@ -201,6 +267,12 @@ drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq)
>> 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;
>> +
>> rq->current_entity = entity;
>> reinit_completion(&entity->entity_idle);
>> spin_unlock(&rq->lock);
>> @@ -210,8 +282,13 @@ drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq)
>> }
>>
>> 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;
>> +
>> rq->current_entity = entity;
>> reinit_completion(&entity->entity_idle);
>> spin_unlock(&rq->lock);
>> @@ -222,20 +299,22 @@ drm_sched_rq_select_entity_rr(struct drm_sched_rq *rq)
>> 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.
>> *
>> * 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)
>> +drm_sched_rq_select_entity_fifo(struct drm_gpu_scheduler *sched,
>> + struct drm_sched_rq *rq)
>> {
>> struct rb_node *rb;
>>
>> @@ -245,6 +324,15 @@ drm_sched_rq_select_entity_fifo(struct drm_sched_rq *rq)
>>
>> 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
>
> * whose job might not fit and wait until we get space for
> Three fixes: ^ ^ ^
>
>> + * this one in terms of fairness.
>
> * this one in terms of credit availability.
>
> It's not the "fairness", it's the number of credits we check for in drm_sched_can_queue() below.
>
>> + */
>> + if (!drm_sched_can_queue(sched, entity)) {
>> + rb = NULL;
>> + break;
>> + }
>> +
>
> That's good.
>
>> rq->current_entity = entity;
>> reinit_completion(&entity->entity_idle);
>> break;
>> @@ -266,18 +354,6 @@ static void drm_sched_run_job_queue(struct drm_gpu_scheduler *sched)
>> queue_work(sched->submit_wq, &sched->work_run_job);
>> }
>>
>> -/**
>> - * drm_sched_can_queue -- Can we queue more to the hardware?
>> - * @sched: scheduler instance
>> - *
>> - * Return true if we can push more jobs to the hw, otherwise false.
>> - */
>> -static bool drm_sched_can_queue(struct drm_gpu_scheduler *sched)
>> -{
>> - return atomic_read(&sched->hw_rq_count) <
>> - sched->hw_submission_limit;
>> -}
>> -
>> /**
>> * drm_sched_select_entity - Select next entity to process
>> *
>> @@ -291,14 +367,11 @@ drm_sched_select_entity(struct drm_gpu_scheduler *sched)
>> struct drm_sched_entity *entity;
>> int i;
>>
>> - if (!drm_sched_can_queue(sched))
>> - return NULL;
>> -
>> /* Kernel run queue has higher priority than normal run queue*/
>> for (i = sched->num_rqs - 1; i >= DRM_SCHED_PRIORITY_MIN; 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]);
>> + drm_sched_rq_select_entity_fifo(sched, sched->sched_rq[i]) :
>> + drm_sched_rq_select_entity_rr(sched, sched->sched_rq[i]);
>> if (entity)
>> break;
>> }
>> @@ -353,7 +426,7 @@ 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->credits, &sched->credit_count);
>> atomic_dec(sched->score);
>>
>> trace_drm_sched_process_job(s_fence);
>> @@ -576,7 +649,7 @@ 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->credits, &sched->credit_count);
>> } else {
>> /*
>> * remove job from pending_list.
>> @@ -637,7 +710,7 @@ 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->credits, &sched->credit_count);
>>
>> if (!full_recovery)
>> continue;
>> @@ -718,6 +791,8 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs);
>> * drm_sched_job_init - init a scheduler job
>> * @job: scheduler job to init
>> * @entity: scheduler entity to use
>> + * @credits: the number of credits this job contributes to the schedulers
>> + * credit limit
>> * @owner: job owner for debugging
>> *
>> * Refer to drm_sched_entity_push_job() documentation
>> @@ -735,7 +810,7 @@ EXPORT_SYMBOL(drm_sched_resubmit_jobs);
>> */
>> int drm_sched_job_init(struct drm_sched_job *job,
>> struct drm_sched_entity *entity,
>> - void *owner)
>> + u32 credits, void *owner)
>> {
>> if (!entity->rq) {
>> /* This will most likely be followed by missing frames
>> @@ -752,6 +827,7 @@ int drm_sched_job_init(struct drm_sched_job *job,
>> return -ENOMEM;
>>
>> INIT_LIST_HEAD(&job->list);
>> + job->credits = credits ? credits : 1;
>>
>> xa_init_flags(&job->dependencies, XA_FLAGS_ALLOC);
>>
>> @@ -961,12 +1037,14 @@ 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);
>> }
>>
>> @@ -1104,7 +1182,7 @@ 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->credits, &sched->credit_count);
>> drm_sched_job_begin(sched_job);
>>
>> trace_drm_run_job(sched_job, entity);
>> @@ -1139,7 +1217,7 @@ static void drm_sched_run_job_work(struct work_struct *w)
>> * @submit_wq: workqueue to use for submission. If NULL, an ordered wq is
>> * allocated and used
>> * @num_rqs: number of runqueues, one for each priority, up to DRM_SCHED_PRIORITY_COUNT
>> - * @hw_submission: number of hw submissions that can be in flight
>> + * @credit_limit: the number of 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
>> @@ -1153,14 +1231,14 @@ 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,
>> - u32 num_rqs, unsigned hw_submission, unsigned hang_limit,
>> + u32 num_rqs, u32 credit_limit, unsigned hang_limit,
>> long timeout, struct workqueue_struct *timeout_wq,
>> atomic_t *score, const char *name, struct device *dev)
>> {
>> int i, ret;
>>
>> sched->ops = ops;
>> - sched->hw_submission_limit = hw_submission;
>> + sched->credit_limit = credit_limit;
>> sched->name = name;
>> if (submit_wq) {
>> sched->submit_wq = submit_wq;
>> @@ -1211,7 +1289,7 @@ 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->credit_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 e5a6166eb152..a911b3f5917e 100644
>> --- a/include/drm/gpu_scheduler.h
>> +++ b/include/drm/gpu_scheduler.h
>> @@ -321,6 +321,7 @@ 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.
>> + * @credits: the number of 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
>> @@ -340,6 +341,8 @@ struct drm_sched_job {
>> struct drm_gpu_scheduler *sched;
>> struct drm_sched_fence *s_fence;
>>
>> + u32 credits;
>> +
>> /*
>> * work is used only after finish_cb has been used and will not be
>> * accessed anymore.
>> @@ -463,13 +466,29 @@ 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.
>> + *
>
> This whole paragraph isn't very clear of what update_job_credits does.
> Perhaps a simple and straightforward name would be more clear:
> get_job_credits: Returns the number of credits this job would
> take.
>
>> + * 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.
>
> The word "update" is confusing here and it implies that DRM should keep track
> of the previous value this function had returned.
>
> Perhaps we can just say:
> * This callback returns the number of credits this job would take if pushed
> * to the driver/hardware. It returns 0, if this job would take no credits.
>
> Else, driver writers would have to deduce what to return here by looking at
> drm_sched_can_queue() which effectively does:
> s_job->credits = sched->ops->update_job_credits(s_job).
>
>> + *
>> + * This callback is optional.
>> + */
>> + u32 (*update_job_credits)(struct drm_sched_job *sched_job);
>> };
>>
>
> The rest is good--thanks for the changes!
>
>> /**
>> * struct drm_gpu_scheduler - scheduler instance-specific data
>> *
>> * @ops: backend operations provided by the driver.
>> - * @hw_submission_limit: the max size of the hardware queue.
>> + * @credit_limit: the credit limit of this scheduler
>> + * @credit_count: the current credit count of this scheduler
>> * @timeout: the time after which a job is removed from the scheduler.
>> * @name: name of the ring for which this scheduler is being used.
>> * @num_rqs: Number of run-queues. This is at most DRM_SCHED_PRIORITY_COUNT,
>> @@ -478,7 +497,6 @@ struct drm_sched_backend_ops {
>> * @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
>> @@ -502,13 +520,13 @@ struct drm_sched_backend_ops {
>> */
>> struct drm_gpu_scheduler {
>> const struct drm_sched_backend_ops *ops;
>> - uint32_t hw_submission_limit;
>> + u32 credit_limit;
>> + atomic_t credit_count;
>> long timeout;
>> const char *name;
>> u32 num_rqs;
>> struct drm_sched_rq **sched_rq;
>> 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;
>> @@ -530,14 +548,14 @@ 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,
>> - u32 num_rqs, uint32_t hw_submission, unsigned hang_limit,
>> + u32 num_rqs, u32 credit_limit, unsigned hang_limit,
>> long timeout, struct workqueue_struct *timeout_wq,
>> atomic_t *score, const char *name, struct device *dev);
>>
>> void drm_sched_fini(struct drm_gpu_scheduler *sched);
>> int drm_sched_job_init(struct drm_sched_job *job,
>> struct drm_sched_entity *entity,
>> - void *owner);
>> + u32 credits, void *owner);
>> void drm_sched_job_arm(struct drm_sched_job *job);
>> int drm_sched_job_add_dependency(struct drm_sched_job *job,
>> struct dma_fence *fence);
>> @@ -559,7 +577,8 @@ 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_wqueue_ready(struct drm_gpu_scheduler *sched);
>> void drm_sched_wqueue_stop(struct drm_gpu_scheduler *sched);
>> void drm_sched_wqueue_start(struct drm_gpu_scheduler *sched);
>
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