[PATCH 1/4] drm/sched: optimize drm_sched_job_add_dependency a bit

[Tvrtko Ursulin]

On 22/05/2025 14:41, Christian König wrote:
> Since we already iterated over the xarray we know at which index the new
> entry should be stored. So instead of using xa_alloc use xa_store and
> write into the index directly.
> 
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>   drivers/gpu/drm/scheduler/sched_main.c | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index f7118497e47a..d2d64bf17c96 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -871,10 +871,8 @@ EXPORT_SYMBOL(drm_sched_job_arm);
>   int drm_sched_job_add_dependency(struct drm_sched_job *job,
>   				 struct dma_fence *fence)
>   {
> +	unsigned long index = -1;
>   	struct dma_fence *entry;
> -	unsigned long index;
> -	u32 id = 0;
> -	int ret;
>   
>   	if (!fence)
>   		return 0;
> @@ -896,11 +894,13 @@ int drm_sched_job_add_dependency(struct drm_sched_job *job,
>   		return 0;
>   	}
>   
> -	ret = xa_alloc(&job->dependencies, &id, fence, xa_limit_32b, GFP_KERNEL);
> -	if (ret != 0)
> +	entry = xa_store(&job->dependencies, index + 1, fence, GFP_KERNEL);

 From the code it looks index does not "move" for NULL slots?

That is, if someone:

1) Preallocates one entry, when trying to populate it index will be -1 
after xa_for_each?

2) Add one, preallocate one, then add one more - index will be 0 after 
xa_for_each?

Regards,

Tvrtko

> +	if (xa_is_err(entry))
>   		dma_fence_put(fence);
> +	else
> +		WARN_ON(entry);
>   
> -	return ret;
> +	return xa_err(entry);
>   }
>   EXPORT_SYMBOL(drm_sched_job_add_dependency);
>