[PVE-User] Regression on virtio-net ? (Was: Re: Proxmox VE 4.2 released!)

[Alexandre DERUMIER]

I think this is related to :

https://www.redhat.com/archives/vfio-users/2016-April/msg00032.html

----- Mail original -----
De: "Wolfgang Bumiller" <w.bumiller at proxmox.com>
À: "Gilou" <contact+dev at gilouweb.com>
Cc: "proxmoxve" <pve-user at pve.proxmox.com>, "aderumier" <aderumier at odiso.com>
Envoyé: Mercredi 11 Mai 2016 12:36:28
Objet: Re: [PVE-User] Regression on virtio-net ? (Was: Re: Proxmox VE 4.2 released!)

On Tue, May 10, 2016 at 01:37:27PM +0200, Gilou wrote: 
> Le 09/05/2016 15:33, Alexandre DERUMIER a écrit : 
> > For v6 (skylake), I think they are new feature implementation in kvm 
> > http://www.gossamer-threads.com/lists/linux/kernel/2267259 
> > 
> > for v4, I don't see any recent change 
> > 
> > 
> > You can reproduce with both v4 and v6 ? 
> 
> Yes, though again m y lab is unavailable for this, so I can't do it 
> "again". But it was a 4xxx & 6xxx that showed the issue in the first place. 
> 
> I just tried on a 4xxx I have on my laptop, it has the issue (using 
> kvm/ubuntu rather than Proxmox, but still) 

After bisecting it seems this commit is the issue: 
https://github.com/torvalds/linux/commit/aca6ff29c4063a8d467cdee241e6b3bf7dc4a171 

Can you try loading the kvm module with these options: 
halt_poll_ns_grow=0 halt_poll_ns_shrink=0 

(/etc/modprobe.d + reboot, or grub boot commandline (with the `kvm.` 
prefix to the options), or just: 
# rmmod kvm-intel 
# rmmod kvm 
# modprobe kvm halt_poll_ns_grow=0 halt_poll_ns_shrink=0 
# modprobe kvm-intel 
) 

This should revert the behavior of this commit. In my test VM this 
commit bumps my load from 60% to 100% with the same 'perf' output you 
had, and setting these options revert it back to normal.