Re: [PATCH 1/2] drm/sched: add drm_sched_prealloc_dependency_slots

[Christian König <ckoenig.leichtzumerken@xxxxxxxxx>]

> > + *
> > + * Return:
> > + * 0 on success, or an error on failing to expand the array.
> > + */
> > +int drm_sched_job_prealloc_dependency_slots(struct drm_sched_job
> > *job,
> > +					    unsigned int num_deps)
> > +{
> > +	struct dma_fence *fence;
> > +	u32 id = 0;
> > +	int ret;
> > +
> > +	while (num_deps--) {
> > +		fence = dma_fence_get_stub();
> > +		ret = xa_alloc(&job->dependencies, &id, fence,
> > xa_limit_32b,
> > +			       GFP_KERNEL);
> >       
> So this would fill the xarr with already signaled fences which then
> later will be replaced with unsignaled fences?
>     
    
    Yes, exactly that's the idea.
    
> Help me out here: would it also work to add NULL instead of that stub-
> fence?
>     
    
    Good question, idk. That's an implementation detail of the xarray.
    
    Tvrtko also correctly pointed out that it is most likely a bad idea
    to use dma_fence_is_signaled() in the critical code path.
    
    I will try to dig through the xarray behavior up and update the
    patch if possible.
    
    Thanks,
    Christian.