RadeonSI Resorts To Disabling SDMA For GFX9/Vega Due To APU Issues

[phoronix]

Phoronix: RadeonSI Resorts To Disabling SDMA For GFX9/Vega Due To APU Issues

AMD's RadeonSI Gallium3D driver has resorted to disabling SDMA (System DMA) async DMA engine support for all GFX9/Vega hardware due to issues plaguing some APUs...

http://www.phoronix.com/scan.php?page=news_item&px=RadeonSI-Disables-GFX9-SDMA

[wizard69]

Well that sucks. If this is an APU only issue why not disable the feature just on those platforms?

[bezirg]

It would be nice if Michael can spin up a benchmark for the effects of this change. Also does this bug affect renoir apus as well?

[aufkrawall]

The effect on games by disabling it for Polaris was close to non-existent in my own tests while it got rid of nasty corruption throughout the bank. If the same is true for this case as well, this would be a welcome change. Let's see this through pragmatic goggles.

[theriddick]

I wonder if the NAVI APU's (5000 model?) will have this issue or if its specific to Vega.

[bridgman]

I wonder if the NAVI APU's (5000 model?) will have this issue or if its specific to Vega.

Marek knows a lot more about this but my recollection is that we got better performance on Navi without SDMA and are not using it.

It's probably fair to say that for most of our chips performance improvements in GFX (shader copy, CPDMA copy) have been pretty significant while SDMA has not improved at the same pace so each year the benefit of SDMA goes down while the overhead of managing and synchronizing with a separate engine stays more or less constant.

[Mthw]

...rendering issues/corruption on Raven...

Like having screen artifacts after resuming from sleep? I do have this issue.

[Nille_kungen]

I don't have any artifacts with my 2500u.

[agd5f]

SDMA was designed for handling transfers from system memory to vram. It's design bandwidth aligns with that. Shaders are designed to take advantage of as much bandwidth as possible. The primary use case for SDMA is in the kernel driver where it's used for paging and other memory management related tasks.

[leipero]

I don't have any artifacts with my 2500u.

Neither on Picasso. I do have different issue with linux with iGPU clocks randomly getting stuck at X frequency, but that's not related to Mesa anyway, and I'm not reporting it as an bug until I rule out UEFI/system issue.