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

[Peter Lieven]

Am 13.11.2012 um 17:33 schrieb Michael S. Tsirkin:

> On Tue, Nov 13, 2012 at 06:22:56PM +0200, 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.
>> 
> 
> Tried with upstream qemu on rhel kernel and that's even a bit faster.
> So it's ubuntu kernel. vanilla 2.6.32 didn't have vhost at all
> so maybe their vhost backport is broken insome way.

That might be. I think Dietmar was reporting that he had problems
with Debian. They likely use the same back port.

Is it correct that with kernel_irqchip the IRQs are
delivered to all vCPUs? Without kernel_irqchip (in qemu-kvm 1.0.1
for instance) they where delivered only to vCPU 0. This scenario
was working.

Peter