Hi, Danilo
On 9/11/23 19:49, Danilo Krummrich wrote:
Hi Thomas,
On 9/11/23 19:19, Thomas Hellström wrote:
Hi, Danilo
On 9/9/23 17:31, Danilo Krummrich wrote:
This patch adds an abstraction layer between the drm_gpuva mappings of
a particular drm_gem_object and this GEM object itself. The abstraction
represents a combination of a drm_gem_object and drm_gpuvm. The
drm_gem_object holds a list of drm_gpuvm_bo structures (the structure
representing this abstraction), while each drm_gpuvm_bo contains
list of
mappings of this GEM object.
This has multiple advantages:
1) We can use the drm_gpuvm_bo structure to attach it to various lists
of the drm_gpuvm. This is useful for tracking external and evicted
objects per VM, which is introduced in subsequent patches.
2) Finding mappings of a certain drm_gem_object mapped in a certain
drm_gpuvm becomes much cheaper.
3) Drivers can derive and extend the structure to easily represent
driver specific states of a BO for a certain GPUVM.
The idea of this abstraction was taken from amdgpu, hence the credit
for
this idea goes to the developers of amdgpu.
Cc: Christian König <christian.koenig@xxxxxxx>
Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
Did you consider having the drivers embed the struct drm_gpuvm_bo in
their own bo definition? I figure that would mean using the gem bo's
refcounting and providing a helper to call from the driver's bo
release. Looks like that could potentially save a lot of code? Or is
there something that won't work with that approach?
There are drm_gpuvm_ops::vm_bo_alloc and drm_gpuvm_ops::vm_bo_free
callback for drivers to register for that purpose.
- Danilo
Now after looking a bit deeper, I think actually the question could be
rephrased as, why don't we just use the
struct drm_gem_object::gpuva struct as the drm_gpuvm_bo in the spirit of
keeping things simple? Drivers would then just embed it in their bo
subclass and we'd avoid unnecessary fields in the struct drm_gem_object
for drivers that don't do VM_BIND yet.
Sure, this won't be per bo and per vm, but it'd really only make a
slight difference where we have multiple VMAs per bo, where per-vm
per-bo state either needs to be duplicated or attached to a single vma
(as in the case of the external bo list).
To me that looks like a substantial amount of less code / complexity?
/Thomas
Thanks,
Thomas
