Re: Virtio network performance poorer than emulated e1000

Sridhar Samudrala
2010-07-23T00:18:28Z

On Thu, 2010-07-22 at 19:53 -0400, Balachandar wrote:
> I am resending this email as Freddie didn't use 'reply to all' when
> replying to this message. I am also updating to answer Freddie's
> questions..
>
> I can see that virtio network performance is poorer than emaulated
> e1000 nic. I did some simple ping test and with emulated e1000 the
> average rtt is around 600 microsec. With virtio the average rtt is 800
> microsec. I am using a tap + bridge configuration. I run kvm as
> follows
>
> kvm -m 512 -hda vdisk.img \
> -net nic,model=virtio \
> -net tap,ifname=tap0,script=qemu-ifup,downscript=no

With newer qemu-kvm, you need to use -netdev tap to enable checksum/gso
offloads.

Try
-net nic,model=virtio,netdev=tap0
-netdev tap,ifname=tap0,id=tap0,vhost=on,script=qemu-ifup,downscript=no

Thanks
Sridhar
>
> I am running Debian squeeze distribution with guest and host kernel 2.6.34.
>
> Does anyone else see some results like this or is it only me? Could
> changing the distribution help as i am running a testing one?
>
> Actually we are having a custom application which just measures
> ping-pong latency. The results that i get with virtio is around 750
> micro seconds. The result i get with emulated e1000 is around 250
> micro sec. Also i tried to use vhost but the virtio latency remained
> the same.
>
> Also i tried the tests with guest and host 2.6.26 kernel. I get better
> results for virtio than e1000. I get 550 for e1000 and 500 for virtio.
>
> Actually my application needs as minimum latency as needed. I am ready
> to trade-off throughput and cpu utilization. I was very excited when i
> saw the vhost-net module with people claiming low latencies. I am
> worried that i am missing some performance offered by virtio and
> vhost.
>
>
> Thanks,
> Bala
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html