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

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Kirill_AGA

New Member
Jul 17, 2018
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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
 
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).
 
UPD: It worked! Setting kvm_intel.preemption_timer to N did the trick and all my VMs are lightning fast again. :D;):cool:
 
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