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

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Nov 13, 2012 at 05:27:17PM +0100, Peter Lieven wrote:
> 
> 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.

You mean on tap? Same thing.

> the bug seems to be only relevant when vhost-net is used.
> 
> Dietmar, see you implications with normal virtio?
> 
> Peter