[vfio-users] Huge performance decrease in VM

[Hristo Iliev]

Hi,

I don't know if this is of any relevance to your case, but recently I 
have been pulling my hair over an issue with the intel_pstate driver in 
the newer Arch Linux kernels. The problem is that the CPU gets stuck at 
the lowest frequency and nothing can bring it out of that state. As a 
result, my Windows VM starts lagging terribly as the latency of the 
emulated interrupts raises significantly.

You can check with powertop or i7z the frequency and if all cores are 
suspiciously stuck at the same low frequency (1.2 GHz on my i7-5820K) no 
matter the system load, then switching the governor to "performance" 
might resolve it:

sudo cpupower frequency-set -g performance

In my case, this results in the CPU getting stuck at the nominal 
frequency and restoring the governor to "powersave" does nothing to 
bring it out of that state. Which is fine, given how often I have to 
reboot due to kernel upgrades :)

Kind regards,

Hristo

Am 06.01.2017 13:00, schrieb Marius Steffen:
> Hi,
> I'm running my VM on Arch for quite some time now, with varying success
> on this hardware:
> 
> - NVIDIA GTX 1070
> - 16 GB RAM (10 GB passed through to VM, tested with/without hugepages)
> - i7 3770 (4 Cores, 4 Hyperthreads, various combinations tested)
> - virtualized OS is Windows 10 Home x64
> 
> Arch is using my iGPU (unvirtualized), usally running KDE Plasma 5, but
> I also tried without running any X-Session.
> 
> As I recently noticed when upgrading my GPU from a GTX 680 to my 
> current
> GTX 1070, there's an extremely huge performance impact compared to
> running on native Windows.
> When playing Just Cause 3, this was especially noteable: I've often got
> only 40-50 FPS, compared to 75-120+ FPS in Windows 10, and my GPU being
> used just about 20% or so in the VM.
> 
> Is there anything I can do to a) find the cause of this bad performance
> b) make my VM perform better?
> 
> Greetings,
> 
> Marius
> 
> 
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