Re: [PATCH] drm/sched: Clarify docu concerning drm_sched_job_arm()

[Philipp Stanner <phasta@mailbox.org>]

On Thu, 2025-03-13 at 11:07 +0100, Christian König wrote:
> Am 13.03.25 um 10:30 schrieb Philipp Stanner:
> > The documentation for drm_sched_job_arm() and especially
> > drm_sched_job_cleanup() does not make it very clear why
> > drm_sched_job_arm() is a point of no return, which it indeed is.
> > 
> > Make the nature of drm_sched_job_arm() in the docu as clear as
> > possible.
> > 
> > Suggested-by: Christian König <christian.koenig@amd.com>
> > Signed-off-by: Philipp Stanner <phasta@kernel.org>
> 
> Reviewed-by: Christian König <christian.koenig@amd.com>

Thx

> 
> I'm currently looking into how to fix the amdgpu CS path for gang
> submission regarding this.
> 
> Any objections that I add a preload function to allocate the memory
> for the XA outside of the critical section?

I can't fully follow, you mean when creating the dependencies xarray?

I think in a perfect world we wouldn't have any more functions that
only have 1 user to work around driver-internal problems. That said, I
realize that the world isn't perfect. Would still be cool if every
function we add would be useful to >1 driver.

I think it's probably best if you just propose sth in form of a patch
and we discuss it there

Grüße
P.


> 
> Regards,
> Christian.
> 
> > ---
> >  drivers/gpu/drm/scheduler/sched_main.c | 24 ++++++++++++++++++----
> > --
> >  1 file changed, 18 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/scheduler/sched_main.c
> > b/drivers/gpu/drm/scheduler/sched_main.c
> > index 4d4219fbe49d..829579c41c6b 100644
> > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > @@ -828,11 +828,15 @@ EXPORT_SYMBOL(drm_sched_job_init);
> >   *
> >   * This arms a scheduler job for execution. Specifically it
> > initializes the
> >   * &drm_sched_job.s_fence of @job, so that it can be attached to
> > struct dma_resv
> > - * or other places that need to track the completion of this job.
> > + * or other places that need to track the completion of this job.
> > It also
> > + * initializes sequence numbers, which are fundamental for fence
> > ordering.
> >   *
> >   * Refer to drm_sched_entity_push_job() documentation for locking
> >   * considerations.
> >   *
> > + * Once this function was called, you *must* submit @job with
> > + * drm_sched_entity_push_job().
> > + *
> >   * This can only be called if drm_sched_job_init() succeeded.
> >   */
> >  void drm_sched_job_arm(struct drm_sched_job *job)
> > @@ -1017,9 +1021,12 @@ EXPORT_SYMBOL(drm_sched_job_has_dependency);
> >   * Drivers should call this from their error unwind code if @job
> > is aborted
> >   * before drm_sched_job_arm() is called.
> >   *
> > - * After that point of no return @job is committed to be executed
> > by the
> > - * scheduler, and this function should be called from the
> > - * &drm_sched_backend_ops.free_job callback.
> > + * drm_sched_job_arm() is a point of no return since it
> > initializes the fences
> > + * and their sequence number etc. Once that function has been
> > called, you *must*
> > + * submit it with drm_sched_entity_push_job() and cannot simply
> > abort it by
> > + * calling drm_sched_job_cleanup().
> > + *
> > + * This function should be called in the
> > &drm_sched_backend_ops.free_job callback.
> >   */
> >  void drm_sched_job_cleanup(struct drm_sched_job *job)
> >  {
> > @@ -1027,10 +1034,15 @@ void drm_sched_job_cleanup(struct
> > drm_sched_job *job)
> >  	unsigned long index;
> >  
> >  	if (kref_read(&job->s_fence->finished.refcount)) {
> > -		/* drm_sched_job_arm() has been called */
> > +		/* The job has been processed by the scheduler,
> > i.e.,
> > +		 * drm_sched_job_arm() and
> > drm_sched_entity_push_job() have
> > +		 * been called.
> > +		 */
> >  		dma_fence_put(&job->s_fence->finished);
> >  	} else {
> > -		/* aborted job before committing to run it */
> > +		/* The job was aborted before it has been
> > committed to be run;
> > +		 * notably, drm_sched_job_arm() has not been
> > called.
> > +		 */
> >  		drm_sched_fence_free(job->s_fence);
> >  	}
> >  
>