[Mesa-dev] [PATCH] radeonsi/gfx9: compile shaders with +xnack

[Marek Olšák]

On Thu, May 18, 2017 at 11:23 PM, Matt Arsenault <arsenm2 at gmail.com> wrote:
>
>> On May 18, 2017, at 22:46, Marek Olšák <maraeo at gmail.com> wrote:
>>
>> From: Marek Olšák <marek.olsak at amd.com>
>>
>> so that LLVM doesn't allocate SGPRs where XNACK is.
>>
>> Cc: 17.1 <mesa-stable at lists.freedesktop.org>
>
> You shouldn’t be explicitly enabling xnack. This sounds like a workaround for a backend bug, and this has other consequences than changing the reserved registers. Do you have an example of where this is a problem?

What are the other consequences?

We don't want XNACK on Carrizo/Stoney, because XNACK is always
disabled on the graphics ring. It's only enabled on compute rings,
which we don't use. GFX9 enables XNACK on all rings at the moment.

XNACK AKA instruction replay is a per-VMID setting in the kernel
driver and it might change in the future. It's not a fixed property of
the GPU architecture.

Marek