[PATCH 6/9] drm/amdgpu: Set/clear CPU_ACCESS_REQUIRED flag on page fault and CS

[Marek Olšák]

On Mon, Jun 26, 2017 at 11:27 AM, Michel Dänzer <michel at daenzer.net> wrote:
> On 25/06/17 03:00 AM, Christian König wrote:
>> Am 23.06.2017 um 19:39 schrieb John Brooks:
>>> When the AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED flag is given by
>>> userspace,
>>> it should only be treated as a hint to initially place a BO somewhere CPU
>>> accessible, rather than having a permanent effect on BO placement.
>>
>> And that is a clear NAK from my side.
>>
>> CPU_ACCESS_REQUIRED is a permanent limitation to where the buffer should
>> be placed.
>
> It really can't be more than a hint. The userspace driver cannot
> reliably know ahead of time whether a BO will be accessed by the CPU at
> all, let alone how often. A BO which incorrectly has this flag set
> creates artificial pressure on CPU visible VRAM.

I also think the flag is only a hint and shouldn't be taken too seriously.

Only AMDGPU_GEM_CREATE_NO_CPU_ACCESS has a strict behavior.

Marek