[PVE-User] network transfer VM 100% CPU load

Gilles Mocellin gilles.mocellin at nuagelibre.org
Fri Sep 12 11:17:35 CEST 2014

Le 12/09/2014 10:21, Tonči Stipičević a écrit :
> Hello to all
> I'm experiencing very very strange (for me) scenario .
> I have installed kvm win 2012r2 server with all virtio drivers.
> At first test results were great :
> 1. copying large file inside VM ->  average 100MB/s   virito disk
> driver does great job (ide was 3 times slower)
> 2. copying large file from VM (logged with rdp to VM and transfer
> initiated from this VM) to another physical server -> approx 90MB/s  
> alomost 1G saturated all the time
> 3. but when the transfer is initiated from the physical machine to the
> VM   then transfer speed lowers down  to the 20MB/s (average)
> and VM CPU load  goes up to 100%  and blocks the whole server and
> server stops serving data at all

I remember some similar problems.
I had resolved it by deactivation General Receive Offload and Large
Receive Offload on my Ethernet cards.

Try that on your interfaces :
ethtool --offload eth0 gro off lro off

If it works, you can fix it in the /etc/network/interface with :

iface eth0 inet manual
  offload-lro off
  offload-gro off

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