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


From: Peter Lieven
Subject: Re: [Qemu-devel] slow virtio network with vhost=on and multiple cores
Date: Fri, 9 Nov 2012 18:27:18 +0100
User-agent: SquirrelMail/1.4.21

Dietmar Maurer wrote:
>> Dietmar, how is the speed if you specify --machine pc,kernel_irqchip=off
>> as
>> cmdline option to qemu-kvm-1.2.0?
>
> I get full speed if i use that flag.
>
>

I also tried to reproduce it and can confirm your findings. Host Ubuntu
12.04 LTS (kernel 3.2) with vanilla qemu-kvm 1.2.0, vhost-net and an
Ubuntu 10.4.4 (Linux 2.6.32) as guest. Vhost-Net performance drops by
approx. factor 50-100 if I do not disable kernel_irqchip. Normal Virtio
and e1000 seems to work fine.




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