On Thu, Jul 22, 2010 at 8:18 PM, Sridhar Samudrala <samudrala.sridhar@xxxxxxxxx> wrote: > 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 tried this one also but not much improvement. Actually i get a some improvement if i disabled the tx timeout timer in the virtio_net.h in qemu-kvm. I read that with vhost the data flow path differs from normal operation. So is the timeout applicable when we use vhost also? Actually i dont see any improvement with vhost. I am just wondering what am i missing? The thing that worries me is that emulated nic offers much greater performance than virtio with vhost. So i feel i am doing something wrong but unable to find it. >> 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@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
