[PATCH libdrm] amdgpu: add amdgpu_bo_handle_type_kms_noimport

[Christian König]

Am 16.07.2018 um 18:05 schrieb Michel Dänzer:
> On 2018-07-13 08:47 PM, Marek Olšák wrote:
>> On Fri, Jul 13, 2018 at 4:28 AM, Michel Dänzer <michel at daenzer.net> wrote:
>>> On 2018-07-12 07:03 PM, Marek Olšák wrote:
>>>> On Thu, Jul 12, 2018, 3:31 AM Michel Dänzer <michel at daenzer.net> wrote:
>>>>> What is the rationale for this? I.e. why do you want to not store some
>>>>> handles in the hash table?
>>>>
>>>> Because I have the option.
>>> Seems like you're expecting this patch to be accepted without providing
>>> any real justification for it (here or in the corresponding Mesa patch).
>>> NAK from me if so.
>> The real justification is implied by the patch. See: amdgpu_add_handle_to_table
>> Like I said: There is no risk of regression and it simplifies one
>> simple case trivially. We shouldn't have to even talk about it.
> IMO you haven't provided enough justification for adding API which is
> prone to breakage if used incorrectly.
>
> Other opinions?

I understand the reason why Marek wants to do this, but I agree that 
this is a little bit dangerous if used incorrectly.

On the other hand I don't see any other way to sanely handle it either.

>
>
>>> I'd rather add the handle to the hash table in amdgpu_bo_alloc,
>>> amdgpu_create_bo_from_user_mem and amdgpu_bo_import instead of in
>>> amdgpu_bo_export, making amdgpu_bo_export(bo, amdgpu_bo_handle_type_kms,
>>> ...) essentially free. In the unlikely (since allocating a BO from the
>>> kernel is expensive) case that the hash table shows up on profiles, we
>>> can optimize it.
>> The hash table isn't very good for high BO counts. The time complexity
>> of a lookup is O(n).
> A lookup is only needed in amdgpu_bo_import. amdgpu_bo_alloc and
> amdgpu_create_bo_from_user_mem can just add the handle to the hash
> bucket directly.
>
> Do you know of, or can you imagine, any workload where amdgpu_bo_import
> is called often enough for this to be a concern?

MM interop with GFX usually imports BOs on each frame, so that can hurt 
here.

Christian.