[PATCH 1/2] drm/amdgpu: return bo itself if userptr is cpu addr of bo (v3)

[Marek Olšák]

On Wed, Aug 1, 2018 at 1:52 PM, Christian König
<christian.koenig at amd.com> wrote:
> Am 01.08.2018 um 19:39 schrieb Marek Olšák:
>>
>> On Wed, Aug 1, 2018 at 2:32 AM, Christian König
>> <christian.koenig at amd.com> wrote:
>>>
>>> Am 01.08.2018 um 00:07 schrieb Marek Olšák:
>>>>
>>>> Can this be implemented as a wrapper on top of libdrm? So that the
>>>> tree (or hash table) isn't created for UMDs that don't need it.
>>>
>>>
>>> No, the problem is that an application gets a CPU pointer from one API
>>> and
>>> tries to import that pointer into another one.
>>>
>>> In other words we need to implement this independent of the UMD who
>>> mapped
>>> the BO.
>>
>> Yeah, it could be an optional feature of libdrm, and other components
>> should be able to disable it to remove the overhead.
>
>
> The overhead is negligible, the real problem is the memory footprint.
>
> A brief look at the hash implementation in libdrm showed that this is
> actually really inefficient.
>
> I think we have the choice of implementing a r/b tree to map the CPU pointer
> addresses or implement a quadratic tree to map the handles.
>
> The later is easy to do and would also allow to get rid of the hash table as
> well.

We can also use the hash table from mesa/src/util.

I don't think the overhead would be negligible. It would be a log(n)
insertion in bo_map and a log(n) deletion in bo_unmap. If you did
bo_map+bo_unmap 10000 times, would it be negligible?

Marek