Am 06.03.2018 um 19:15 schrieb Michel Dänzer:
On 2018-03-06 07:02 PM, Christian König wrote:
Am 06.03.2018 um 18:51 schrieb Michel Dänzer:
On 2018-03-06 06:44 PM, Christian König wrote:
Am 06.03.2018 um 18:22 schrieb Li, Samuel:
addition to that I agree with Michel that the module parameter is
overkill.
That I already explained. Currently SG display feature needs to
provide options for all kinds of use cases. All amd drivers so far
provides options, and the default configuration is actually to
allocate everything from GTT when possible.
That isn't job of the kernel to have this parameter. Saying that we
should probably add a DDX and/or environment option to control that.
Why would we need that? It's the kernel driver's job to handle this as
needed.
Buffer placement is specified by the DDX/Mesa, when we override that in
the kernel we just force unnecessary buffer moves.
Userspace just needs a way to know which domains can/should be used for
scanout buffers, e.g. via an info ioctl.


Yeah, but why shouldn't they then make the decision where to place it as well?

See when we enforce a certain placement in the kernel we will just get an unnecessary buffer move with old user space components.

In other words the kernel just needs to advertise that the hw/sw combination allows scanout from GTT as well and then an updated userspace can actually make use of that placement or decide to not use it in certain situations. E.g. the last time I tested it placing things into GTT still resulted in quite a performance penalty for rendering.

The major use case I can currently see are A+A laptop, cause there it can avoid the additional buffer move from GTT to VRAM for the APU.

Regards,
Christian.
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