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

[Alexandre DERUMIER]

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
> >>
> >>
> >