[PATCH 1/3] drm/amdgpu: add AMDGPU_GEM_CREATE_DISCARDABLE

[Christian König]

Hi Marek,

Am 10.05.22 um 22:43 schrieb Marek Olšák:
> A better flag name would be:
> AMDGPU_GEM_CREATE_BEST_PLACEMENT_OR_DISCARD

A bit long for my taste and I think the best placement is just a side 
effect.

>
> Marek
>
> On Tue, May 10, 2022 at 4:13 PM Marek Olšák <maraeo at gmail.com> wrote:
>
>     Does this really guarantee VRAM placement? The code doesn't say
>     anything about that.
>

Yes, see the code here:

>
>         diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>         b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>         index 8b7ee1142d9a..1944ef37a61e 100644
>         --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>         +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>         @@ -567,6 +567,7 @@ int amdgpu_bo_create(struct amdgpu_device
>         *adev,
>                         bp->domain;
>                 bo->allowed_domains = bo->preferred_domains;
>                 if (bp->type != ttm_bo_type_kernel &&
>         +           !(bp->flags & AMDGPU_GEM_CREATE_DISCARDABLE) &&
>                     bo->allowed_domains == AMDGPU_GEM_DOMAIN_VRAM)
>                         bo->allowed_domains |= AMDGPU_GEM_DOMAIN_GTT;
>

The only case where this could be circumvented is when you try to 
allocate more than physically available on an APU.

E.g. you only have something like 32 MiB VRAM and request 64 MiB, then 
the GEM code will catch the error and fallback to GTT (IIRC).

Regards,
Christian.
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