[PATCH v4 02/10] drm/sched: Convert drm scheduler to use a work queue rather than kthread

[Tvrtko Ursulin]

On 05/10/2023 05:13, Luben Tuikov wrote:
> On 2023-10-04 23:33, Matthew Brost wrote:
>> On Tue, Sep 26, 2023 at 11:32:10PM -0400, Luben Tuikov wrote:
>>> Hi,
>>>
>>> On 2023-09-19 01:01, Matthew Brost wrote:
>>>> In XE, the new Intel GPU driver, a choice has made to have a 1 to 1
>>>> mapping between a drm_gpu_scheduler and drm_sched_entity. At first this
>>>> seems a bit odd but let us explain the reasoning below.
>>>>
>>>> 1. In XE the submission order from multiple drm_sched_entity is not
>>>> guaranteed to be the same completion even if targeting the same hardware
>>>> engine. This is because in XE we have a firmware scheduler, the GuC,
>>>> which allowed to reorder, timeslice, and preempt submissions. If a using
>>>> shared drm_gpu_scheduler across multiple drm_sched_entity, the TDR falls
>>>> apart as the TDR expects submission order == completion order. Using a
>>>> dedicated drm_gpu_scheduler per drm_sched_entity solve this problem.
>>>>
>>>> 2. In XE submissions are done via programming a ring buffer (circular
>>>> buffer), a drm_gpu_scheduler provides a limit on number of jobs, if the
>>>> limit of number jobs is set to RING_SIZE / MAX_SIZE_PER_JOB we get flow
>>>> control on the ring for free.
>>>>
>>>> A problem with this design is currently a drm_gpu_scheduler uses a
>>>> kthread for submission / job cleanup. This doesn't scale if a large
>>>> number of drm_gpu_scheduler are used. To work around the scaling issue,
>>>> use a worker rather than kthread for submission / job cleanup.
>>>>
>>>> v2:
>>>>    - (Rob Clark) Fix msm build
>>>>    - Pass in run work queue
>>>> v3:
>>>>    - (Boris) don't have loop in worker
>>>> v4:
>>>>    - (Tvrtko) break out submit ready, stop, start helpers into own patch
>>>> v5:
>>>>    - (Boris) default to ordered work queue
>>>>
>>>> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
>>>> ---
>>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_device.c |   2 +-
>>>>   drivers/gpu/drm/etnaviv/etnaviv_sched.c    |   2 +-
>>>>   drivers/gpu/drm/lima/lima_sched.c          |   2 +-
>>>>   drivers/gpu/drm/msm/msm_ringbuffer.c       |   2 +-
>>>>   drivers/gpu/drm/nouveau/nouveau_sched.c    |   2 +-
>>>>   drivers/gpu/drm/panfrost/panfrost_job.c    |   2 +-
>>>>   drivers/gpu/drm/scheduler/sched_main.c     | 118 ++++++++++-----------
>>>>   drivers/gpu/drm/v3d/v3d_sched.c            |  10 +-
>>>>   include/drm/gpu_scheduler.h                |  14 ++-
>>>>   9 files changed, 79 insertions(+), 75 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> index e366f61c3aed..16f3cfe1574a 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>> @@ -2279,7 +2279,7 @@ static int amdgpu_device_init_schedulers(struct amdgpu_device *adev)
>>>>   			break;
>>>>   		}
>>>>   
>>>> -		r = drm_sched_init(&ring->sched, &amdgpu_sched_ops,
>>>> +		r = drm_sched_init(&ring->sched, &amdgpu_sched_ops, NULL,
>>>>   				   ring->num_hw_submission, 0,
>>>>   				   timeout, adev->reset_domain->wq,
>>>>   				   ring->sched_score, ring->name,
>>>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_sched.c b/drivers/gpu/drm/etnaviv/etnaviv_sched.c
>>>> index 345fec6cb1a4..618a804ddc34 100644
>>>> --- a/drivers/gpu/drm/etnaviv/etnaviv_sched.c
>>>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_sched.c
>>>> @@ -134,7 +134,7 @@ int etnaviv_sched_init(struct etnaviv_gpu *gpu)
>>>>   {
>>>>   	int ret;
>>>>   
>>>> -	ret = drm_sched_init(&gpu->sched, &etnaviv_sched_ops,
>>>> +	ret = drm_sched_init(&gpu->sched, &etnaviv_sched_ops, NULL,
>>>>   			     etnaviv_hw_jobs_limit, etnaviv_job_hang_limit,
>>>>   			     msecs_to_jiffies(500), NULL, NULL,
>>>>   			     dev_name(gpu->dev), gpu->dev);
>>>> diff --git a/drivers/gpu/drm/lima/lima_sched.c b/drivers/gpu/drm/lima/lima_sched.c
>>>> index ffd91a5ee299..8d858aed0e56 100644
>>>> --- a/drivers/gpu/drm/lima/lima_sched.c
>>>> +++ b/drivers/gpu/drm/lima/lima_sched.c
>>>> @@ -488,7 +488,7 @@ int lima_sched_pipe_init(struct lima_sched_pipe *pipe, const char *name)
>>>>   
>>>>   	INIT_WORK(&pipe->recover_work, lima_sched_recover_work);
>>>>   
>>>> -	return drm_sched_init(&pipe->base, &lima_sched_ops, 1,
>>>> +	return drm_sched_init(&pipe->base, &lima_sched_ops, NULL, 1,
>>>>   			      lima_job_hang_limit,
>>>>   			      msecs_to_jiffies(timeout), NULL,
>>>>   			      NULL, name, pipe->ldev->dev);
>>>> diff --git a/drivers/gpu/drm/msm/msm_ringbuffer.c b/drivers/gpu/drm/msm/msm_ringbuffer.c
>>>> index 40c0bc35a44c..b8865e61b40f 100644
>>>> --- a/drivers/gpu/drm/msm/msm_ringbuffer.c
>>>> +++ b/drivers/gpu/drm/msm/msm_ringbuffer.c
>>>> @@ -94,7 +94,7 @@ struct msm_ringbuffer *msm_ringbuffer_new(struct msm_gpu *gpu, int id,
>>>>   	 /* currently managing hangcheck ourselves: */
>>>>   	sched_timeout = MAX_SCHEDULE_TIMEOUT;
>>>>   
>>>> -	ret = drm_sched_init(&ring->sched, &msm_sched_ops,
>>>> +	ret = drm_sched_init(&ring->sched, &msm_sched_ops, NULL,
>>>>   			num_hw_submissions, 0, sched_timeout,
>>>>   			NULL, NULL, to_msm_bo(ring->bo)->name, gpu->dev->dev);
>>>
>>> checkpatch.pl complains here about unmatched open parens.
>>>
>>
>> Will fix and run checkpatch before posting next rev.
>>
>>>>   	if (ret) {
>>>> diff --git a/drivers/gpu/drm/nouveau/nouveau_sched.c b/drivers/gpu/drm/nouveau/nouveau_sched.c
>>>> index 88217185e0f3..d458c2227d4f 100644
>>>> --- a/drivers/gpu/drm/nouveau/nouveau_sched.c
>>>> +++ b/drivers/gpu/drm/nouveau/nouveau_sched.c
>>>> @@ -429,7 +429,7 @@ int nouveau_sched_init(struct nouveau_drm *drm)
>>>>   	if (!drm->sched_wq)
>>>>   		return -ENOMEM;
>>>>   
>>>> -	return drm_sched_init(sched, &nouveau_sched_ops,
>>>> +	return drm_sched_init(sched, &nouveau_sched_ops, NULL,
>>>>   			      NOUVEAU_SCHED_HW_SUBMISSIONS, 0, job_hang_limit,
>>>>   			      NULL, NULL, "nouveau_sched", drm->dev->dev);
>>>>   }
>>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
>>>> index 033f5e684707..326ca1ddf1d7 100644
>>>> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
>>>> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
>>>> @@ -831,7 +831,7 @@ int panfrost_job_init(struct panfrost_device *pfdev)
>>>>   		js->queue[j].fence_context = dma_fence_context_alloc(1);
>>>>   
>>>>   		ret = drm_sched_init(&js->queue[j].sched,
>>>> -				     &panfrost_sched_ops,
>>>> +				     &panfrost_sched_ops, NULL,
>>>>   				     nentries, 0,
>>>>   				     msecs_to_jiffies(JOB_TIMEOUT_MS),
>>>>   				     pfdev->reset.wq,
>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
>>>> index e4fa62abca41..ee6281942e36 100644
>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>>> @@ -48,7 +48,6 @@
>>>>    * through the jobs entity pointer.
>>>>    */
>>>>   
>>>> -#include <linux/kthread.h>
>>>>   #include <linux/wait.h>
>>>>   #include <linux/sched.h>
>>>>   #include <linux/completion.h>
>>>> @@ -256,6 +255,16 @@ drm_sched_rq_select_entity_fifo(struct drm_sched_rq *rq)
>>>>   	return rb ? rb_entry(rb, struct drm_sched_entity, rb_tree_node) : NULL;
>>>>   }
>>>>   
>>>> +/**
>>>> + * drm_sched_submit_queue - scheduler queue submission
>>>
>>> There is no verb in the description, and is not clear what
>>> this function does unless one reads the code. Given that this
>>> is DOC, this should be clearer here. Something like "queue
>>> scheduler work to be executed" or something to that effect.
>>>
>>
>> Will fix.
>>   
>>> Coming back to this from reading the patch below, it was somewhat
>>> unclear what "drm_sched_submit_queue()" does, since when reading
>>> below, "submit" was being read by my mind as an adjective, as opposed
>>> to a verb. Perhaps something like:
>>>
>>> drm_sched_queue_submit(), or
>>> drm_sched_queue_exec(), or
>>> drm_sched_queue_push(), or something to that effect. You pick. :-)
>>>
>>
>> I prefer the name as is. In this patch we have:
>>
>> drm_sched_submit_queue()
>> drm_sched_submit_start)
>> drm_sched_submit_stop()
>> drm_sched_submit_ready()
>>
>> I like all these functions start with 'drm_sched_submit' which allows
>> for easy searching for the functions that touch the DRM scheduler
>> submission state.
>>
>> With a little better doc are you fine with the names as is.
> 
> Notice the following scheme in the naming,
> 
> drm_sched_submit_queue()
> drm_sched_submit_start)
> drm_sched_submit_stop()
> drm_sched_submit_ready()
> \---+---/ \--+-/ \-+-/
>      |        |     +---> a verb
>      |        +---------> should be a noun (something in the component)
>      +------------------> the kernel/software component
> 
> And although "queue" can technically be used as a verb too, I'd rather it be "enqueue",
> like this:
> 
> drm_sched_submit_enqueue()
> 
> And using "submit" as the noun of the component is a bit cringy,
> since "submit" is really a verb, and it's cringy to make it a "state"
> or an "object" we operate on in the DRM Scheduler. "Submission" is
> a noun, but "submission enqueue/start/stop/ready" doesn't sound
> very well thought out. "Submission" really is what the work-queue
> does.
> 
> I'd rather it be a real object, like for instance,
> 
> drm_sched_wqueue_enqueue()
> drm_sched_wqueue_start)
> drm_sched_wqueue_stop()
> drm_sched_wqueue_ready()
> 
> Which tells me that the component is the DRM Scheduler, the object is a/the work-queue,
> and the last word as the verb, is the action we're performing on the object, i.e. the work-queue.
> Plus, all these functions actually do operate on work-queues, directly or indirectly,
> are new, so it's a win-win naming scheme.
> 
> I think that that would be most likeable.

FWIW I was suggesting not to encode the fact submit queue is implemented 
with a workqueue in the API name. IMO it would be nicer and less 
maintenance churn should something channge if the external components 
can be isolated from that detail.

drm_sched_submit_queue_$verb? If not viewed as too verbose...

Regards,

Tvrtko