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

[Christian König]

Am 02.08.2018 um 08:20 schrieb Zhang, Jerry (Junwei):
> On 08/02/2018 08:00 AM, Marek Olšák wrote:
>> On Wed, Aug 1, 2018 at 2:29 PM, Christian König
>> <christian.koenig at amd.com> wrote:
>>> Am 01.08.2018 um 19:59 schrieb Marek Olšák:
>>>> [SNIP]
>>>
>>> Compared to what the kernel needs to do for updating the page tables 
>>> it is
>>> less than 1% of the total work.
>>>
>>> The real question is if it wouldn't be simpler to use a tree for the
>>> handles. Since the handles are dense you can just use an unbalanced 
>>> tree
>>> which is really easy.
>>>
>>> For a tree of the CPU mappings we would need an r/b interval tree, 
>>> which is
>>> hard to implement and quite some overkill.
>>>
>>> Do you have any numbers how many BOs really get a CPU mapping in a real
>>> world application?
>>
>> Without our suballocator, we sometimes exceeded the max. mmap limit
>> (~64K). It should be much less with the suballocator with 128KB slabs,
>> probably a few thousands.
>
> Is there a way to verify that it has performance issue if moving the 
> cpu mapping in libdrm hash table
> from kernel side?

Going to take a look at this, but I have the feeling that the CPU 
overhead we need to add in userspace isn't that much.

>
> AFAIW, only one game will use that with close OGL.

Well, I would also say that this is a bug in the game and should be 
fixed there.

Christian.

>
> Regards,
> Jerry
>
>>
>> Marek
>>