[PATCH 1/3] drm/sched: Add internal job peek/pop API

[Tvrtko Ursulin]

On 06/02/2025 16:54, Danilo Krummrich wrote:
> On Thu, Feb 06, 2025 at 04:40:29PM +0000, Tvrtko Ursulin wrote:
>> Idea is to add helpers for peeking and popping jobs from entities with
>> the goal of decoupling the hidden assumption in the code that queue_node
>> is the first element in struct drm_sched_job.
>>
>> That assumption usually comes in the form of:
>>
>>    while ((job = to_drm_sched_job(spsc_queue_pop(&entity->job_queue))))
>>
>> Which breaks if the queue_node is re-positioned due to_drm_sched_job
>> being implemented with a container_of.
>>
>> This also allows us to remove duplicate definitions of to_drm_sched_job.
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
>> Cc: Christian König <christian.koenig at amd.com>
>> Cc: Danilo Krummrich <dakr at kernel.org>
>> Cc: Matthew Brost <matthew.brost at intel.com>
>> Cc: Philipp Stanner <phasta at kernel.org>
>> ---
>>   drivers/gpu/drm/scheduler/sched_entity.c   | 11 +++---
>>   drivers/gpu/drm/scheduler/sched_internal.h | 43 ++++++++++++++++++++++
>>   drivers/gpu/drm/scheduler/sched_main.c     |  7 ++--
>>   3 files changed, 51 insertions(+), 10 deletions(-)
>>   create mode 100644 drivers/gpu/drm/scheduler/sched_internal.h
>>
>> diff --git a/drivers/gpu/drm/scheduler/sched_internal.h b/drivers/gpu/drm/scheduler/sched_internal.h
>> new file mode 100644
>> index 000000000000..565c83e32371
>> --- /dev/null
>> +++ b/drivers/gpu/drm/scheduler/sched_internal.h
>> @@ -0,0 +1,43 @@
>> +
>> +
>> +/**
>> + * __drm_sched_entity_queue_pop - Low level helper for popping queued jobs
> 
> Why the '__' prefix?

True, it is a remnant from v1 when I had it in gpu_scheduler.h because 
then double underscores were supposed to signal this is "special" 
(internal) API. After adding sched_internal.h it makes no more sense. I 
will drop them.

Speaking of sched_internal.h, as a follow up we could also move a bunch 
of other prototypes from gpu_scheduler.h in there.

> Could also use this to replace spsc_queue_pop() in drm_sched_entity_pop_job().

We could but as that caller does not want/need the job returned maybe 
okay not to. Open to change if you insist.

>> + *
>> + * @entity: scheduler entity
>> + *
>> + * Low level helper for popping queued jobs.
>> + *
>> + * Returns the job dequeued or NULL.
>> + */
>> +static inline struct drm_sched_job *
>> +__drm_sched_entity_queue_pop(struct drm_sched_entity *entity)
>> +{
>> +	struct spsc_node *node;
>> +
>> +	node = spsc_queue_pop(&entity->job_queue);
>> +	if (!node)
>> +		return NULL;
>> +
>> +	return container_of(node, struct drm_sched_job, queue_node);
>> +}
>> +
>> +/**
>> + * __drm_sched_entity_queue_peek - Low level helper for peeking at the job queue
> 
> Same here.
> 
> Could also use this for drm_sched_entity_is_ready().

Again we could but that one does not want a job but just a does a "queue 
not empty" check. Could replace also with spsc_queue_count() to make 
that clearer.

Regards,

Tvrtko

>> + *
>> + * @entity: scheduler entity
>> + *
>> + * Low level helper for peeking at the job queue
>> + *
>> + * Returns the job at the head of the queue or NULL.
>> + */
>> +static inline struct drm_sched_job *
>> +__drm_sched_entity_queue_peek(struct drm_sched_entity *entity)
>> +{
>> +	struct spsc_node *node;
>> +
>> +	node = spsc_queue_peek(&entity->job_queue);
>> +	if (!node)
>> +		return NULL;
>> +
>> +	return container_of(node, struct drm_sched_job, queue_node);
>> +}
>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
>> index a48be16ab84f..43ca98e8db5f 100644
>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>> @@ -78,6 +78,8 @@
>>   #include <drm/gpu_scheduler.h>
>>   #include <drm/spsc_queue.h>
>>   
>> +#include "sched_internal.h"
>> +
>>   #define CREATE_TRACE_POINTS
>>   #include "gpu_scheduler_trace.h"
>>   
>> @@ -87,9 +89,6 @@ static struct lockdep_map drm_sched_lockdep_map = {
>>   };
>>   #endif
>>   
>> -#define to_drm_sched_job(sched_job)		\
>> -		container_of((sched_job), struct drm_sched_job, queue_node)
>> -
>>   int drm_sched_policy = DRM_SCHED_POLICY_FIFO;
>>   
>>   /**
>> @@ -123,7 +122,7 @@ static bool drm_sched_can_queue(struct drm_gpu_scheduler *sched,
>>   {
>>   	struct drm_sched_job *s_job;
>>   
>> -	s_job = to_drm_sched_job(spsc_queue_peek(&entity->job_queue));
>> +	s_job = __drm_sched_entity_queue_peek(entity);
>>   	if (!s_job)
>>   		return false;
>>   
>> -- 
>> 2.48.0
>>