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

[Christian König]

On 5/22/25 16:27, Tvrtko Ursulin wrote:
> 
> 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?

Correct, but I just found out that the macro initializes index to zero, so that approach also doesn't work.

*sigh* going to look into this again tomorrow. It looks like this use case is somehow not well supported at all by xarray.

Regards,
Christian.

> 
> 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);
>>   
>