Re: [Qemu-devel] slow virtio network with vhost=on and multiple cores

[Peter Lieven]

Am 13.11.2012 um 17:26 schrieb Michael S. Tsirkin:

> On Tue, Nov 13, 2012 at 05:21:50PM +0100, Peter Lieven wrote:
>> On 13.11.2012 17:22, Michael S. Tsirkin wrote:
>>> On Tue, Nov 13, 2012 at 12:49:03PM +0100, Peter Lieven wrote:
>>>> On 09.11.2012 19:03, Peter Lieven wrote:
>>>>> Remark:
>>>>> If i disable interrupts on CPU1-3 for virtio the performance is ok again.
>>>>> 
>>>>> Now we need someone with deeper knowledge of the in-kernel irqchip and the
>>>>> virtio/vhost driver development to say if this is a regression in qemu-kvm
>>>>> or a problem with the old virtio drivers if they receive the interrupt on
>>>>> different CPUs.
>>>> anyone?
>>> Looks like the problem is not in the guest: I tried ubuntu guest
>>> on a rhel host, I got 8GB/s with vhost and 4GB/s without
>>> on a host to guest banchmark.
>> which ubuntu version in the guest?
>> 
>> Peter
> 
> ubuntu-10.04.4-server-amd64.iso

can you try with vnet_hdr=on on the nic.

the bug seems to be only relevant when vhost-net is used.

Dietmar, see you implications with normal virtio?

Peter