Re: [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.koe...@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);