[PATCH] D40047: AMDGPU/GCN: Remove xnack from 801 and 810

[Marek Olšák via Phabricator via llvm-commits]

mareko added a comment.

In https://reviews.llvm.org/D40047#926553, @t-tye wrote:

> Did notice that for Mesa3D XNACK is being forcibly disabled for all targets <gfx9 and forcibly enabled for all targets >=gfx9. Is that the best choice? It seems it will likely not match how the driver is configuring the hardware. For example, how does the driver configure the APUs? Is XNACK always being enabled for gfx9 (it is not for compute)?


Mesa can't modify SH_MEM_CONFIG to enable/disable XNACK. What is hardcoded in the kernel is what we get. XNACK is only enabled on compute rings on gfx8 APUs and on all rings on gfx9. In practice, Mesa should never access an unmapped page. I don't know if setting -xnack on all chips is a good idea in that case. We might also have suboptimal performance on gfx9 due to XNACK being always enabled by the KMD.


https://reviews.llvm.org/D40047