[RFC 03/10] drm/i915/vm_bind: Support private and shared BOs

[Hellstrom, Thomas]

On Fri, 2022-07-08 at 15:43 +0200, Thomas Hellström wrote:
> > The vm_bind/bound_list and the non_priv_vm_bind_list are there for
> > very different reasons.
> > 
> > The reason for having separate vm_bind_list and vm_bound_list is
> > that
> > during the execbuf path, we can rebind the unbound mappings by
> > scooping
> > all unbound vmas back from bound list into the bind list and
> > binding
> > them. In fact, this probably can be done with a single vm_bind_list
> > and
> > a 'eb.bind_list' (local to execbuf3 ioctl) for rebinding.
> > 
> > The non_priv_vm_bind_list is just an optimization to loop only
> > through
> > non-priv objects while taking the locks in
> > eb_lock_persistent_vmas()
> > as only non-priv objects needs that (private objects are locked in
> > a
> > single shot with vm_priv_lock). A non-priv mapping will also be in
> > the
> > vm_bind/bound_list.
> > 
> > I think, we need to add this as documentation to be more clear.
> 
> OK, I understood it as private objects were either on the vm_bind
> list
> or vm_bound_list depending on whether they needed rebinding or not,
> and
> shared objects only on the non_priv_vm_bind list, and were always
> locked, validated and fenced...
> 
> Need to take a deeper look...
> 
> /Thomas
> 
> 
> 
> > 
> > Niranjana
> > 
> > 

Hmm. Just a quick thought on this, Since the non-private vm-bind
objects all need to be iterated through (locked and fenced and userptr
valid) on each execbuf, and checking for validation (resident and
bound) is a very quick check, then we'd never need to add them to the
rebind list at all, right? If so the rebind list would be exclusive to
vm-private objects.

Also I don't think the vm_bind list can be execbuf-local, since binding
may not have completed at vma_release time, at which point the objects
need to remain on the vm_bind list until the next execbuf...

/Thomas