One more important thing is to make sure you launch vhost thread for your 
virtio nic, as part of Guest instantiation. There will be a parameter 
"vhost=on" in Guest instantiation command line.

-----Original Message-----
From: kvm-ow...@vger.kernel.org [mailto:kvm-ow...@vger.kernel.org] On Behalf Of 
Venkateswara Rao Nandigam
Sent: Thursday, May 15, 2014 10:20 AM
To: JR; kvm@vger.kernel.org
Subject: RE: Poor performance with virtio network driver on windows 2008 R2 on 
KVM

Try TSO offload on Guest Virtio interface

And try passthrough interface mode at Host Level for this Guest Virtio Interface

Thanks,
Venkatesh

-----Original Message-----
From: kvm-ow...@vger.kernel.org [mailto:kvm-ow...@vger.kernel.org] On Behalf Of 
JR
Sent: Wednesday, May 14, 2014 9:07 PM
To: kvm@vger.kernel.org
Subject: Poor performance with virtio network driver on windows 2008 R2 on KVM

Greetings all,

Though I don't believe that this is KVM problem per se, I'm seeing very poor 
network performance when using windows 2008R2 KVM instances with the virtio 
driver when on a 10G network.  iperf results show linux VMs getting close to 
wire speeds, while windows only does about 1.3Gb/sec.

I've tried a number of tcp settings (chimney, etc...) as recommended by some 
google searches but nothing has helped.

Does anyone have any advice?

Thanks much,
JR


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