Re: [PATCH libdrm] amdgpu: add amdgpu_bo_handle_type_kms_noimport

["Michel Dänzer" <michel-otUistvHUpPR7s880joybQ@public.gmane.org>]

On 2018-07-16 08:51 PM, Marek Olšák wrote:
> On Mon, Jul 16, 2018 at 12:05 PM, Michel Dänzer <michel@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@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
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