linux-kernel - Re: how to optimize virtio-vhost in 10G net

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Date:	Sun, 15 Feb 2015 07:48:32 +0008
From:	Jason Wang <jasowang@...hat.com>
To:	Ding Xiao <ssdxiaoding@...il.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: how to optimize virtio-vhost in 10G net



On Sun, Feb 15, 2015 at 3:30 PM, Ding Xiao <ssdxiaoding@...il.com> 
wrote:
> I am test virtio-vhost in 10G environment
> 
> host info
> cpu E2680@...GHz
> memory 16G
> network intel 82599BE
> os centos 7
> 
> VM info
> cpu 4
> memory 4G
> network using virtio vhost
> os centos 7
> 
> I using pktgen to send udp package, the result like follow
> 64b 230Mb/s
> 1400b 5.9Gb/s
> 
> I test the speed in VMware too, the result like follow
> 64b 700Mb/s
> 1400 9.3Gb/s
> 
> I am very surprised why the speed with virtio-vhost is slow
> so I test to analysis this by using perf tool
> I found the tun_sendmsg occupancy rate of 35%

It looks like you're using pktgen in guest. Pktgen has known issue with 
driver that does not have tx completion. See discussion here: 
https://patchwork.kernel.org/patch/1800711/

So you can't trust pktgen result in this case.
> 
> tun_sendmsg using copy_from_user to get the data from VM
> Perhaps mapping could improve the performance ?

If you enable vhost_net zerocopy, you will see obvious improvements.
> 
> or other Another improvement method ?

I suggest that you can use other benchmark tools (or apply the patch in 
the above link with pktgen).
> 
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