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Date: Tue, 13 Nov 2012 19:03:14 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] slow virtio network with vhost=on and multiple
	cores
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To: Peter Lieven <pl@dlhnet.de>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, Peter Lieven <lieven-lists@dlhnet.de>, Jan Kiszka <jan.kiszka@web.de>, Dietmar Maurer <dietmar@proxmox.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

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