AW: current qemu-kvm doesn't work with vhost

[Georg Hopp <georg@steffers.org>]

Am 19.06.2011 10:58:20 schrieb(en) Jan Kiszka:
> On 2011-06-17 22:31, Georg Hopp wrote:
> > Am 17.06.2011 09:29:41 schrieb(en) Jan Kiszka:
> >> On 2011-06-17 09:10, Georg Hopp wrote:
> >> > Jan Kiszka <jan.kiszka <at> web.de> writes:
> >> >>
> >> >> On 2011-06-10 05:08, Amos Kong wrote:
> >> >>> host kernel: 2.6.39-rc2+
> >> >>> qemu-kvm : 05f1737582ab6c075476bde931c5eafbc62a9349
> >> >>>
> >> >>> (gdb) r -monitor stdio -m 800 ~/RHEL-Server-6.0-64-virtio.qcow2
> >> -snapshot
> >> > -device
> >> >> virtio-net-pci,netdev=he -netdev tap,vhost=on,id=he
> >> >>>
> >> >>
> >> >> I already came across that symptom in a different context.  
> Fixed by
> >> the
> >> >> patch below.
> >> >>
> >> >> However, the real issue is related to an upstream cleanup of the
> >> >> virtio-pci build. That reveals some unneeded build dependencies  
> in
> >> >> qemu-kvm. Will post a fix.
> >> >>
> >> >> Jan
> >> >
> >> > FYI
> >> >
> >> > I encountered the same problem and applied the patch.
> >> >
> >> > Well this results in the following error while starting the  
> guest:
> >> >
> >> >  qemu-system-x86_64: unable to start vhost net: 38:
> >> >   falling back on userspace virtio
> >> >
> >> > and i have no network at all. I will disable vhost=on for now.
> >>
> >> Hmm, works fine for me. The vhost-net module is loaded (though I  
> got a
> >> different message when I forgot to load it)?
> >>
> >> Jan
> >>
> >
> > Generally it works for me until git revision b2146d8bd.
> 
> You mean including that commit, right?
> 
> >
> > I have compiled vhost-net directly in my kernel so a have definetly  
> not
> > forgotten to load it...
> > As i use gentoo i made an ebuild that installes exactly this  
> revision.
> > If i find the time to do some debugging i will do so, but actually  
> i am
> > very busy with my job
> > family and the use of kvm is just a sparetime thing. :D
> >
> > If it would be of some help i can set a breakpoint just before the  
> path
> > and see what
> > causes the message.
> 
> Let's start with double-checking that you are on ce5f0a588b, did a  
> make
> clean && make, and then actually used that result. I suspect an
> inconsistent build as ce5f0a588b makes the difference between ENOSYS
> (38) and working vhost support here.
> 
> Jan
> 
> 

Hi again,

tried the current HEAD without any patches and vhost works again for me
and with much better performance than before.

------------------------------------------------------------
Client connecting to host, TCP port 5001
TCP window size: 16.0 KByte (default)
------------------------------------------------------------
[  3] local 192.168.100.4 port 48053 connected with 192.168.100.1 port  
5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  7.63 GBytes  6.55 Gbits/sec

Thanks for the great work!

Greets
    Georg