Re: Network poblems using virtio and tap.

[Fabian Deutsch <fabian.deutsch@gmx.de>]

Am Samstag, den 06.09.2008, 14:26 +0200 schrieb richard lucassen:
> On Sat, 06 Sep 2008 14:04:30 +0200
> Fabian Deutsch <fabian.deutsch@gmx.de> wrote:
> 
> > Am Samstag, den 06.09.2008, 09:40 +0200 schrieb Christian Borntraeger:
> > > Am Montag, 1. September 2008 schrieb Fabian Deutsch:
> > > > Hey.
> > > > 
> > > > I'm observing some network problems when using virtio and a tap
> > > > if. The trouble is a drop of network troughput from abot 90Mbit/s
> > > > to
> > about 
> > > 90kbit/s,
> > > > after about 1.7 TB of transferred data.
> > > > 
> > > > Setup
> > > > Host: 
> > > > - Fedora 8, nearly all updates
> > > > - Intel(R) Xeon(R) CPU           X3210  @ 2.13GHz
> > > > - 8GB RAM
> > > > - 2 Guests
> > > > 
> > > > Guest:
> > > > - Fedora 9 all updates
> > > > - virtio nic using tap
> > > > - samba sharing a mountpoint using an iscsi target
> > > 
> > > Can you tell us what host kernel and what guest kernel you are
> > > using?
> > The were 
> > > some changes to tun/tap for virtio lately which could make a
> > difference.
> > 
> > Host:
> > Fedora 8 x86_64
> > 2.6.25.14-69.fc8 SMP
> > kvm-72
> > 
> > Guest:
> > Fedora 9 i386
> > 2.6.25.11-97.fc9.i686
> 
> I noticed the same behaviour using a rtl8139 and a tap device. After
> some MB's (!) I had to invoke a in the guest:
> 
> ifdown eth0; ifup eth0

ifdown ; ifup doesn't help in this case.
Even a guest-restart "init 6" doesn't help.
Just shutting it completely down "init 0" and powering it on again
helps.

> 
> to get the network back again. I replaced the rtl-8139 by a virtio
> device and the problem seems to have gone, but I haven't tried yet with
> a large amount of data.

Virtio net works fast and withouth trouble - up to some point, then
packet loss occurs.

> 
> kvm-73 (kvm74 gives compile errors)
> host: 64bit ubuntu-8.04-LTS with vanilla kernel 2.6.26.3 SMP
> guest: ubuntu-8.04-LTS with ubuntu kernel 32-bit
> 
> On the same host runs a 32bit w2k3 (virtio NIC) and I haven't noticed
> such problems, even when this host ran with an rtl-8139 device.
> 
> Sorry if I missed some postings concerning the issue, I just
> (re)subscribed to the list.
> 
> R.
>