[PATCH 1/2] drm/amdgpu: Enable scatter gather display support

[Michel Dänzer]

On 2018-03-07 10:47 AM, Christian König wrote:
> Am 07.03.2018 um 09:42 schrieb Michel Dänzer:
>> On 2018-03-06 07:23 PM, Christian König wrote:
>>
>>> E.g. the last time I tested it placing things into GTT still resulted
>>> in quite a performance penalty for rendering.
>> FWIW, I think the penalty is most likely IOMMU related. Last time I
>> tested, I couldn't measure a big difference with IOMMU disabled.
> 
> No, the penalty I'm talking about came from the ping/pong we did with
> the scanout buffers.
> 
> See when I tested this the DDX and Mesa where unmodified, so both still
> assumed VRAM as placement for scanout BOs, but the kernel forced scanout
> BOs into GTT for testing.
> 
> So what happened was that on scanout we moved the VRAM BO to GTT and
> after unpinning it on the first command submission which used the BO we
> moved it back to VRAM again.

In the meantime, I've had the same idea as Marek: Can't the kernel
driver simply change the BO's preferred domain to GTT when scanning out
from it? Then it won't move back to VRAM.


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