Re: [PATCH v5 4/4] drm/amdgpu: track bo memory stats at runtime

[Tvrtko Ursulin <tvrtko.ursulin@igalia.com>]

On 23/10/2024 13:56, Christian König wrote:
> Am 23.10.24 um 14:24 schrieb Tvrtko Ursulin:
>> [SNIP]
>>>> To fold or not the special placements (GWS, GDS & co) is also 
>>>> tangential. In my patch I just preserved the legacy behaviour so it 
>>>> can easily be tweaked on top.
>>>
>>> Yeah, but again the original behavior is completely broken.
>>>
>>> GWS, GDS and OA are counted in blocks of HW units (multiplied by 
>>> PAGE_SIZE IIRC to avoid some GEM&TTM warnings).
>>>
>>> When you accumulate that anywhere in the memory stats then that is 
>>> just completely off.
>>
>> Ooops. :) Are they backed by some memory though, be it system or VRAM?
> 
> GDS is an internal 4 or 64KiB memory block which is only valid while 
> shaders are running. It is used to communicate stuff between different 
> shader stages and not even CPU accessible.
> 
> GWS and OA are not even memory, those are just HW blocks which implement 
> a fixed function.
> 
> IIRC most HW generation have 16 of each and when setting up the 
> application virtual address space you can specify how many will be used 
> by the application.

I see, thank you! Though I could have bothered to look in the code or 
even instrument at runtime too.

I agree removing it from system is correct. If wanted and/or desirable 
some or all could be exported as different memory regions even. DRM 
fdinfo specs already allows that. Like:

drm-total-vram: ...
drm-total-gds: ...
drm-total-oa: ...

Etc.

Regards,

Tvrtko