[PATCH xserver 1/2] modesetting: Fix reverse prime partial update issues on secondary GPU outputs

[Hans de Goede]

Hi,

On 09/20/2016 03:24 AM, Michel Dänzer wrote:
> On 17/09/16 01:38 AM, Eric Anholt wrote:
>> Keith Packard <keithp at keithp.com> writes:
>>> Hans de Goede <hdegoede at redhat.com> writes:
>>>
>>>> So it looks like we really need glFinish to ensure proper ordering here
>>>> (and I've just deleted the v2 of this patchset with flush with I had
>>>> prepared).
>>>
>>> If you need glFinish, then your drivers are broken. glFlush and suitable
>>> fences provides sufficient information to allow for synchronization
>>> between operations without also requiring waiting for the hardware to
>>> finish. It's a difference between getting things into the hardware
>>> queues in the right order and waiting for those hardware queues to
>>> drain.
>>
>> glFlush by the spec does provide any guarantees that things have made it
>> to the kernel.  We have just assumed that, but I think the Radeon driver
>> may be violating that assumption these days.
>
> No, it doesn't. It only uses the separate command submission thread for
> internal flushes, e.g. when running out of space for the GPU command
> stream. glFlush still results in a synchronous flush.
>
>
> Hans, which drivers were you seeing the wrong order of operations with?

intel master gpu, slave output on nvidia gpu using nouveau kernel driver
and modesetting xorg driver on both gpus.

 > I assume you were testing with patch 2 of the series applied?

Yes.

Regards,

Hans