Re: [PATCH] drm/xe: Take ref to job's fence in arm

[Matthew Auld <matthew.auld@intel.com>]

On 22/10/2024 18:58, Matthew Brost wrote:
> On Tue, Oct 22, 2024 at 09:39:54AM +0100, Matthew Auld wrote:
>> On 21/10/2024 18:35, Matthew Brost wrote:
>>> Take ref to job's fence in arm rather than run job. This ref is owned by
>>> the drm scheduler so it makes sense to take the ref before handing over
>>> the job to the scheduler. Also removes an atomic from the run job path.
>>>
>>> Suggested-by: Matthew Auld <matthew.auld@intel.com>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> ---
>>>    drivers/gpu/drm/xe/xe_execlist.c        | 2 +-
>>>    drivers/gpu/drm/xe/xe_guc_submit.c      | 9 +++++----
>>>    drivers/gpu/drm/xe/xe_sched_job.c       | 2 +-
>>>    drivers/gpu/drm/xe/xe_sched_job_types.h | 1 -
>>>    4 files changed, 7 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/xe/xe_execlist.c b/drivers/gpu/drm/xe/xe_execlist.c
>>> index f3b71fe7a96d..a8c416a48812 100644
>>> --- a/drivers/gpu/drm/xe/xe_execlist.c
>>> +++ b/drivers/gpu/drm/xe/xe_execlist.c
>>> @@ -313,7 +313,7 @@ execlist_run_job(struct drm_sched_job *drm_job)
>>>    	q->ring_ops->emit_job(job);
>>>    	xe_execlist_make_active(exl);
>>> -	return dma_fence_get(job->fence);
>>> +	return job->fence;
>>>    }
>>>    static void execlist_job_free(struct drm_sched_job *drm_job)
>>> diff --git a/drivers/gpu/drm/xe/xe_guc_submit.c b/drivers/gpu/drm/xe/xe_guc_submit.c
>>> index 0b81972ff651..25f51a947c3a 100644
>>> --- a/drivers/gpu/drm/xe/xe_guc_submit.c
>>> +++ b/drivers/gpu/drm/xe/xe_guc_submit.c
>>> @@ -717,6 +717,7 @@ guc_exec_queue_run_job(struct drm_sched_job *drm_job)
>>>    	struct xe_exec_queue *q = job->q;
>>>    	struct xe_guc *guc = exec_queue_to_guc(q);
>>>    	struct xe_device *xe = guc_to_xe(guc);
>>> +	struct dma_fence *fence = NULL;
>>>    	bool lr = xe_exec_queue_is_lr(q);
>>>    	xe_assert(xe, !(exec_queue_destroyed(q) || exec_queue_pending_disable(q)) ||
>>> @@ -734,12 +735,12 @@ guc_exec_queue_run_job(struct drm_sched_job *drm_job)
>>>    	if (lr) {
>>>    		xe_sched_job_set_error(job, -EOPNOTSUPP);
>>> -		return NULL;
>>> -	} else if (test_and_set_bit(JOB_FLAG_SUBMIT, &job->fence->flags)) {
>>> -		return job->fence;
>>> +		dma_fence_put(job->fence);	/* Drop ref from xe_sched_job_arm */
>>
>> Just to confirm, with lr the run_job here is not going to be run more than
>> once?
>>
> 
> LR mode - at most once as we return NULL run_job so job is immediately
> signaled / removed from pending job list.
> 
> Non-LR mode - after a GT reset it is possible for a job to have run_job
> called a second time. In this case, there is no 'dma_fence_put' in the
> resubmit path which pairs with the 'dma_fence_get' in arm.
> 
> So I think this patch is correct.

Thanks for confirming,
Reviewed-by: Matthew Auld <matthew.auld@intel.com>

> 
> Matt
> 
>>>    	} else {
>>> -		return dma_fence_get(job->fence);
>>> +		fence = job->fence;
>>>    	}
>>> +
>>> +	return fence;
>>>    }
>>>    static void guc_exec_queue_free_job(struct drm_sched_job *drm_job)
>>> diff --git a/drivers/gpu/drm/xe/xe_sched_job.c b/drivers/gpu/drm/xe/xe_sched_job.c
>>> index eeccc1c318ae..1905ca590965 100644
>>> --- a/drivers/gpu/drm/xe/xe_sched_job.c
>>> +++ b/drivers/gpu/drm/xe/xe_sched_job.c
>>> @@ -280,7 +280,7 @@ void xe_sched_job_arm(struct xe_sched_job *job)
>>>    		fence = &chain->base;
>>>    	}
>>> -	job->fence = fence;
>>> +	job->fence = dma_fence_get(fence);	/* Pairs with put in scheduler */
>>>    	drm_sched_job_arm(&job->drm);
>>>    }
>>> diff --git a/drivers/gpu/drm/xe/xe_sched_job_types.h b/drivers/gpu/drm/xe/xe_sched_job_types.h
>>> index 0d3f76fb05ce..8ed95e1a378f 100644
>>> --- a/drivers/gpu/drm/xe/xe_sched_job_types.h
>>> +++ b/drivers/gpu/drm/xe/xe_sched_job_types.h
>>> @@ -40,7 +40,6 @@ struct xe_sched_job {
>>>    	 * @fence: dma fence to indicate completion. 1 way relationship - job
>>>    	 * can safely reference fence, fence cannot safely reference job.
>>>    	 */
>>> -#define JOB_FLAG_SUBMIT		DMA_FENCE_FLAG_USER_BITS
>>>    	struct dma_fence *fence;
>>>    	/** @user_fence: write back value when BB is complete */
>>>    	struct {