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

[Michael S. Tsirkin]

Do you see all interrupts going to the same CPU? If yes is
irqbalance in guest running?

On Mon, Mar 18, 2013 at 10:50:19AM +0100, Alexandre DERUMIER wrote:
> Hello, about this bug,
> 
> 
> Last Proxmox distrib use 2.6.32 rhel 6.3 kernel + qemu 1.4 , and have this 
> problem with guest with 2.6.32 kernel.
> 
> do you think that +x2apic in guest cpu could help ?
> 
> (I think it's enable by default in RHEV/OVIRT ? but not in proxmox)
> 
> 
> 
> ----- Mail original -----
> 
> De: "Michael S. Tsirkin" <address@hidden>
> À: "Peter Lieven" <address@hidden>
> Cc: "Davide Guerri" <address@hidden>, "Alexandre DERUMIER" <address@hidden>, 
> "Stefan Hajnoczi" <address@hidden>, address@hidden, "Jan Kiszka" 
> <address@hidden>, "Peter Lieven" <address@hidden>, "Dietmar Maurer" 
> <address@hidden>
> Envoyé: Dimanche 17 Mars 2013 10:08:17
> Objet: Re: [Qemu-devel] slow virtio network with vhost=on and multiple cores
> 
> On Fri, Mar 15, 2013 at 08:23:44AM +0100, Peter Lieven wrote:
> > On 15.03.2013 00:04, Davide Guerri wrote:
> > >Yes this is definitely an option :)
> > >
> > >Just for curiosity, what is the effect of "in-kernel irqchip"?
> >
> > it emulates the irqchip in-kernel (in the KVM kernel module) which
> > avoids userspace exits to qemu. in your particular case I remember
> > that it made all IRQs deliverd to vcpu0 on. So I think this is a workaround
> > and not the real fix. I think Michael is right that it is a
> > client kernel bug. It would be good to find out what it is and ask
> > the 2.6.32 maintainers to include it. i further have seen that
> > with more recent kernels and inkernel-irqchip the irqs are delivered
> > to vcpu0 only again (without multiqueue).
> >
> > >Is it possible to disable it on a "live" domain?
> >
> > try it. i don't know. you definetely have to do a live migration for it, 
> > but I have no clue if the VM will survice this.
> >
> > Peter
> 
> I doubt you can migrate VMs between irqchip/non irqchip configurations.
> 
> > >
> > >Cheers,
> > > Davide
> > >
> > >
> > >On 14/mar/2013, at 19:21, Peter Lieven <address@hidden> wrote:
> > >
> > >>
> > >>Am 14.03.2013 um 19:15 schrieb Davide Guerri <address@hidden>:
> > >>
> > >>>Of course I can do some test but a kernel upgrade is not an option here 
> > >>>:(
> > >>
> > >>disabling the in-kernel irqchip (default since 1.2.0) should also help, 
> > >>maybe this is an option.
> > >>
> > >>Peter
> > >>
> > >>
> > >