[PATCH 3/4] drm/scheduler: add new function to get least loaded sched

[Christian König]

Am 31.07.2018 um 12:37 schrieb Nayan Deshmukh:
> The function selects the run queue from the rq_list with the
> least load. The load is decided by the number of jobs in a
> scheduler.
>
> Signed-off-by: Nayan Deshmukh <nayan26deshmukh at gmail.com>
> ---
>   drivers/gpu/drm/scheduler/gpu_scheduler.c | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
>
> diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> index 375f6f7f6a93..c67f65ad8f15 100644
> --- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
> +++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> @@ -255,6 +255,32 @@ static bool drm_sched_entity_is_ready(struct drm_sched_entity *entity)
>   	return true;
>   }
>   
> +/**
> + * drm_sched_entity_get_free_sched - Get the rq from rq_list with least load
> + *
> + * @entity: scheduler entity
> + *
> + * Return the pointer to the rq with least load.
> + */
> +static struct drm_sched_rq *
> +drm_sched_entity_get_free_sched(struct drm_sched_entity *entity)
> +{
> +	struct drm_sched_rq *rq = NULL;
> +	unsigned int min_jobs = UINT_MAX;
> +	int i;
> +
> +	for (i = 0; i < entity->num_rq_list; ++i) {
> +		if (atomic_read(&entity->rq_list[i]->sched->num_jobs) <
> +				min_jobs) {
> +			min_jobs = atomic_read(
> +					&entity->rq_list[i]->sched->num_jobs);

When you use atomic_read twice you might get different results because 
the atomic has changed in the meantime.

In other words you need to store the result locally:

unsigned int num_jobs = atomic_read(....);

if (num_jobs < min_jobs) {
     min_jobs = num_jobs;
     .....

Christian.

> +			rq = entity->rq_list[i];
> +		}
> +	}
> +
> +	return rq;
> +}
> +
>   static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
>   				    struct dma_fence_cb *cb)
>   {