Re: [PATCH v9 2/3] drm/amdgpu: Enable clear page functionality

["Michel Dänzer" <michel.daenzer@mailbox.org>]

On 2024-04-02 10:17, Christian König wrote:
> Am 26.03.24 um 15:53 schrieb Alex Deucher:
>> On Tue, Mar 26, 2024 at 10:01 AM Alex Deucher <alexdeucher@gmail.com> wrote:
>>> On Tue, Mar 26, 2024 at 9:59 AM Paneer Selvam, Arunpravin
>>>>>> @@ -501,6 +502,9 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>>>>>>           if (place->flags & TTM_PL_FLAG_CONTIGUOUS)
>>>>>>                   vres->flags |= DRM_BUDDY_CONTIGUOUS_ALLOCATION;
>>>>>>
>>>>>> +       if (bo->flags & AMDGPU_GEM_CREATE_VRAM_CLEARED)
>>>>>> +               vres->flags |= DRM_BUDDY_CLEAR_ALLOCATION;
>>>>> Is there any reason to not always do this?
>>>> Here we are trying to keep a pool of cleared memory which are cleared on
>>>> free path and that can given
>>>> to the application which requires a zeroed memory. I think here if we
>>>> set always clear the memory,
>>>> we would go over the limit of cleared memory in that particular instance
>>>> and the application should wait until
>>>> the hardware clears the memory and this might impact the overall
>>>> performance.
>>> I'd like to have the driver always deliver cleared memory.
>> Actually, I think we can just always set the flag in the allocation IOCTLs.
> 
> We have use cases where that hurts as. Especially during boot when the backing VRAM isn't cleared yet.
> 
> That's one of the reasons why we never always cleared the memory.

Any such performance gain was only valid in the first place if the kernel delivering non-cleared memory to user space was considered acceptable, which it quite clearly isn't.


-- 
Earthling Michel Dänzer            |                  https://redhat.com
Libre software enthusiast          |         Mesa and Xwayland developer