MTRR support in recent driver/card?

Graphics / Linux Linux
1

Sorry for reposting from nvnews forum but I thought I might get a better answer here or perhaps some feedback from nvidia.

I have a GTX 460 using the 310.19 driver.

I’m trying to use it without PAT support. I’m loading the nvidia kernel module driver with NVreg_UsePageAttributeTable=0

From the kernel messages I can see:

[   94.534963] NVRM: loading NVIDIA UNIX x86_64 Kernel Module  310.19  Thu Nov  8 00:52:03 PST 2012
[   94.535125] NVRM: builtin PAT support disabled, falling back to MTRRs.
[  126.927848] NVRM: GPU at 0000:01:00: GPU-2d2df840-6445-2af1-fc01-00f7c8346757

However, it doesn’t seem to be using MTRR, at least I do not see any new MTRR entries in /proc/mtrr after the driver is loaded or after X has started. (I’m expecting to see some new write-combining MTRR region created)

And without PAT and MTRR, 3D performance is dreadful (3-4fps)

Is there something that can be done here?

The reason I’m doing this is I’m trying to use the nvidia card under Xen Dom0. The PAT support in the Xen Dom0 has some big issues and has been disabled. I ended up digging up some old MTRR Xen patches and seems to have got MTRR enabled in Dom0. Now the last step is to get nvidia to use MTRR.

And yes, I know nvidia’s driver + Xen has always been an issue for most non-Quadro cards. I’m just trying to do my best here. At least if I can see the nvidia drver is actually using MTRR then I’ll be happy even if it doesn’t boost the performance.

If someone from nvidia can confirm that MTRR is not being used anymore at all then that’s also a good answer too. Perhaps I will need to use an older version of the driver?

Thanks!

2

MTRR is not flexible enough for modern GPUs to work, so PAT is pretty much required these days. I should note that Xen is explicitly not supported, in part because of things like this. I apologize for the inconvenience.

3

Thanks Aaron.

I know it’s not going to happen overnight, but I read some old posts about Xen support being filed on NVIDIA list internally. Is it still the case?

As for MTRR, is there any chance that an older driver might work?

Thanks again.

4

I have no information about if or when Xen might be supported, sorry.

5

Yet more lies from nVidia as here I am in 2017 using a GTX 1080Ti in KVM on Linux, in Windows, with MTRR. 4 years later and MTRR is still flexible enough. The solution, make sure that Write Back is set for the MTRR.