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SubjectRe: [PATCH drm-misc-next v8 09/12] drm/gpuvm: reference count drm_gpuvm structures
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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.

AMD already made that mistake with KFD and I strongly suggest not to
repeat it :)

Regards,
Christian.

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