[Qemu-devel] netperf performance drop from Virtual machine

[Raj Ravi]

Hi,

I am observing issues with UDP performance issues (with UFO on)  from
inside KVM based VM.

setup details:

1.
In the Host  (say Host1):

ifconfig eth0 0
ifconfig bond0 up
ifenslave bond0 eth0
brctl addbr br0
brctl addif br0 bond0
ifconfig br0

Now,  br0 bridge is used for network interface in VM1.:
    <interface type='bridge'>
    <source bridge='br0'/>
    <model type='virtio'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>

2.
Run netserver in another Host (say Host2).

3.
Now, from inside VM ,run netperf like this:

./src/netperf -4 -H 10.162.103.102 -t UDP_STREAM

I can observe drastic performance drop in VM (netperf output).

Using ethtool, I can observe ufo is switched ON in eth0 inside VM. (
it is based on virtio-net)

4.
>From Host2, I can packet reassembles failed count getting incremented.
(netstat -s)

Any idea about this?  I am facing difficulties in knowing at which
layer exactly packet drop occurs ?
I observed this issue in latest kernel too. (3.16.3) .

Please let me know if anything wrong in my setup.

5.
Also, I can see bridge br0 UFO is initially switched OFF. Once I power
ON VM, bridge UFO turned ON automatically.
VM's eth0 is tied to bridge as I mentioned in XML format.

Is this expected behaviour ??

6.
Now, If I switch OFF ufo in VM, (ethtool -K eth0 ufo off), performance
becomes normal. (around 900 Mbps from 1 Gbps link)

Please let me

Thanks,
Kavi Raj