[PATCH RFC v2] drm/amdgpu: Set/clear CPU_ACCESS flag on page fault and move to VRAM

[Michel Dänzer]

On 01/07/17 12:31 AM, John Brooks wrote:
> When a BO is moved to VRAM, clear AMDGPU_BO_FLAG_CPU_ACCESS. This allows it
> to potentially later move to invisible VRAM if the CPU does not access it
> again.
> 
> Setting the CPU_ACCESS flag in amdgpu_bo_fault_reserve_notify() also means
> that we can remove the loop to restrict lpfn to the end of visible VRAM,
> because amdgpu_ttm_placement_init() will do it for us.
> 
> Signed-off-by: John Brooks <john at fastquake.com>

[...]

> @@ -446,6 +448,12 @@ static int amdgpu_move_ram_vram(struct ttm_buffer_object *bo,
>  	if (unlikely(r)) {
>  		goto out_cleanup;
>  	}
> +
> +	/* The page fault handler will re-set this if the CPU accesses the BO
> +	 * after it's moved.
> +	 */
> +	abo->flags &= ~AMDGPU_BO_FLAG_CPU_ACCESS;

I've come to realize that the flag also needs to be cleared at the end
of amdgpu_bo_create_restricted, otherwise we will incorrectly assume
that every BO created with this flag has been accessed by the CPU.


BTW, there's also a minor issue here in that the flags member is u64,
but the flags are defined as ints. Probably doesn't matter so far, but
it would as soon as any flag's value is >= (1 << 32).


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer