[PATCH libdrm] amdgpu: add amdgpu_bo_handle_type_kms_noimport

[Marek Olšák]

Michel, I think you are wasting your time. This change can be misused
as easily as any other API. It's not more dangerous that any other
amdgpu libdrm function. You won't achieve anything by optimizing the
hash table (= losing time), and you also won't achieve anything by
NAKing this (= losing performance on the lookup). Both are lose-lose
solutions, because you'll lose and others will lose too.

Marek

On Tue, Jul 17, 2018 at 4:57 AM, Michel Dänzer <michel at daenzer.net> wrote:
> On 2018-07-16 08:51 PM, Marek Olšák wrote:
>> On Mon, Jul 16, 2018 at 12:05 PM, Michel Dänzer <michel at daenzer.net> wrote:
>>> 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:
>>>
>>>>> 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?
>>
>> Fullscreen DRI2 or DRI3 re-imports buffers every frame.
>
> DRI3 doesn't. The X server only imports each DRI3 buffer once, after
> that it's referred to via the pixmap XID.
>
>
> With DRI2 page flipping (ignoring that basically nobody's using that
> anymore with radeonsi :), it's always the same set of buffers, so the
> lookup can be made fast as discussed in the sub-thread with Christian.
> (Also, DRI2 can only use page flipping with sync-to-vblank enabled, so
> this happens on the order of hundreds of times per second max)
>
>
> --
> Earthling Michel Dänzer               |               http://www.amd.com
> Libre software enthusiast             |             Mesa and X developer