[vfio-users] AMD Ryzen Nested Page Table Performance Oddities

[Graham Neville]

Has there been any feedback on this at all?

I'm still struggling to get a Windows and Linux VM working at the same time
with npt=1. Annoying as I'm having to reboot in to a different kernel if I
want to use one or the other.

Are you able to share your Kernel command line and XML for the Linux host
please?


On 7 Apr 2017 22:54, "Nick Sarnie" <commendsarnex at gmail.com> wrote:

I can't reproduce that issue, I tested a Fedora VM with both npt 0 and
1, of course with the same GPU performance results as windows. I've
mailed some AMD guys and KVM guys, and hopefully someone can at least
figure out what is going on. Also, Alex has reproduced this himself on
both Nvidia and AMD GPUs.

On Fri, Apr 7, 2017 at 5:49 PM, Graham Neville <grahamneville at gmail.com>
wrote:
> Sarnex,
>
> I have similar oddities with npt with Ryzen. As you say with kvm-amd.npt=0
> the GPU performance is so much better (In my Witcher3 tests I'm going from
> 40fps to 75fps!). However with npt disabled the Windows10 VM slows down an
> awful lot in general tasks.
>
> I've also noticed that I can only run a Linux guest with kvm-amd.npt=0,
if I
> have it set to enabled then the Linux guest fails to start. I have the
same
> issue even just trying to install Linux from an ISO, it will crash at the
> GRUB install menu.
>
> Hopefully someone knows a fix for this.
>
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