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Date: Fri, 27 Oct 2023 16:47:41 +0200
From: Danilo Krummrich <dakr@...hat.com>
To: Luben Tuikov <ltuikov89@...il.com>, airlied@...il.com,
daniel@...ll.ch, matthew.brost@...el.com,
boris.brezillon@...labora.com, christian.koenig@....com,
faith@...strand.net, luben.tuikov@....com
Cc: linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH drm-misc-next v3] drm/sched: implement dynamic job-flow
control
On 10/27/23 03:03, Luben Tuikov wrote:
> 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@...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
>>>
>>> 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.
That's great!
>
> 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.
Yes, as mentioned in my previous reply, gonna address them soon in a V4.
- Danilo
>
> 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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