[libvirt-users] performance with libvirt and kvm

Stefan Hajnoczi stefanha at gmail.com
Wed Aug 4 08:20:09 UTC 2010


On Tue, Aug 3, 2010 at 11:04 PM, Nirmal Guhan <vavatutu at gmail.com> wrote:
> I am seeing a performance degradation while using libvirt to start my
> vm (kvm). vm is fedora 12 and host is also fedora 12, both with
> 2.6.32.10-90.fc12.i686. Here are the statistics from iperf :
>
> From VM: [  3]  0.0-30.0 sec   199 MBytes  55.7 Mbits/sec
[...]
> qemu kvm : [  3]  0.0-30.0 sec   329 MBytes  91.9 Mbits/sec

Is this what you are comparing: 91.9 -> 55.7 Mbits/s?

> Command used : qemu-kvm vdisk.img -m 512 -net nic,model=virtio
> macaddr=$macaddress -net tap,script=/etc/qemu-ifup

Have you tried to bisect the command-lines by dropping options from
the libvirt command-line until you arrive at the manual qemu-kvm
command-line?

Try using your own tap networking instead of libvirt's but otherwise
keeping libvirt's command-line as much as possible.

Can you use /var/lib/libvirt/f12.img with the manual qemu-kvm instead
of the vdisk.img file?  In general, try to compare same with same and
eliminate variables.

Stefan




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