Non-Linux guest performance degradation after upgrade 4.4 -> 5.2

[Kirill_AGA]

Hi all,

After upgrade from discontinued PVE 4.4 to 5.2 I faced quite an unpleasant fact, that all my OpenBSD guests have been slowed down dramatically... After some research I found, that Spectre-related patches can affect performance (does that mean, that last pve-kernel for 4.4 didn't have them?). Funny, but Linux guests haven't been affected at all. I played a bit with different types of processor/flags (PCID, SPEC-CTRL), and disk caches, but did not come to any significant improvement... Any suggestions/ideas?

Cheers,
Kirill

 

[Kirill_AGA]

So... Tried so far without success:

• Disabling hyperthreading
• Playing with various types of emulated CPUs (or exposing the host CPU type to the guest)
• Reducing/increasing number of cores

The only thing really worked — downgrading the kernel to pve-4.4.134-1

At the same time I've found recommendation to set kvm_intel.preemption_timer to N or "0", wanna give it a try (need to wait couple of hours to access the console to bring back the hyperthreading).

 

[Kirill_AGA]

UPD: It worked! Setting kvm_intel.preemption_timer to N did the trick and all my VMs are lightning fast again.

 

[udo]

Hi,
have you installed an new bios to support IBRS? With this you get back most of the perfomance you lost before (but I'm not sure with OpenBSD).

Udo