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Re: [libvirt] Qemu/KVM is 3x slower under libvirt (due to vhost=on)



On 09/28/11 11:53, Daniel P. Berrange wrote:
On Wed, Sep 28, 2011 at 11:49:01AM +0200, Reeted wrote:
YES!
It's the vhost. With vhost=on it takes about 12 seconds more time to boot.

...meaning? :-)
I've no idea. I was always under the impression that 'vhost=on' was
the 'make it go much faster' switch. So something is going wrong
here that I cna't explain.

Perhaps one of the network people on this list can explain...


To turn vhost off in the libvirt XML, you should be able to use
<driver name='qemu'/>  for the interface in question,eg


     <interface type='user'>
       <mac address='52:54:00:e5:48:58'/>
       <model type='virtio'/>
       <driver name='qemu'/>
     </interface>


Ok that seems to work: it removes the vhost part in the virsh launch hence cutting down 12secs of boot time.

If nobody comes out with an explanation of why, I will open another thread on the kvm list for this. I would probably need to test disk performance on vhost=on to see if it degrades or it's for another reason that boot time is increased.

Thanks so much for your help Daniel,
Reeted


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