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

[Reeted]

On 09/28/11 14:56, Richard W.M. Jones wrote:
> On Wed, Sep 28, 2011 at 12:19:09PM +0200, Reeted wrote:
>> 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.
> Is it using CPU during this time, or is the qemu-kvm process idle?
>
> It wouldn't be the first time that a network option ROM sat around
> waiting for an imaginary console user to press a key.
>
> Rich.

Of the two qemu-kvm processes (threads?) which I see consuming CPU for 
that VM, one is at about 20%, the other at about 10%. I think it's doing 
something but maybe not much, or maybe it's really I/O bound and the I/O 
is slow (as I originarily thought). I will perform some disk benchmarks 
and follow up, but I can't do that right now...
Thank you