On 11/13/23 08:22, Christian König wrote:
Am 10.11.23 um 17:57 schrieb Danilo Krummrich:
On 11/10/23 09:50, Christian König wrote:
[SNIP]
Another issue Christian brought up is that something intended to be embeddable
(a base class) shouldn't really have its own refcount. I think that's a valid
point. If you at some point need to derive from multiple such structs each
having its own refcount, things will start to get weird. One way to resolve
that would be to have the driver's subclass provide get() and put() ops, and
export a destructor for the base-class, rather than to have the base-class
provide the refcount and a destructor ops.
GPUVM simply follows the same pattern we have with drm_gem_objects. And I think
it makes
sense. Why would we want to embed two struct drm_gpuvm in a single driver
structure?
Because you need one drm_gpuvm structure for each application using the driver?
Or am I missing something?
Right, *one*, but not more than one. Wasn't that the concern? Maybe I
misunderstood something. :)
Well, there is the use case of native context with XEN/KVM. In that situation
QEMU opens tons of driver file descriptors on behalves of the virtual
environment clients.
In this use case you have many drm_gpuvm instances for a single application. So
you can't assume that you only have one VM per PID/TGID or something like that.
Well, that's fine. I think Xe can have multiple VMs per PID as well. In this
case you'd keep creating driver VM structures with a single GPUVM as base
class. But not multiple GPUVMs serving as base class for a single driver
structure, which I thought was the concern here. For the latter I can't see a
use case.
AMD already made that mistake with KFD and I strongly suggest not to repeat it
:)
Regards,
Christian.
