Re: [Qemu-devel] [Bug 1228285] [NEW] e1000 nic TCP performances

[Stefan Hajnoczi]

On Fri, Sep 20, 2013 at 05:21:23PM -0000, Vincent Autefage wrote:
> Here is the context :
> 
> $ qemu -name A -m 1024 -net nic vlan=0,model=e1000 -net 
> socket,vlan=0,listen=127.0.0.1:7000
> $ qemu -name B -m 1024 -net nic vlan=0,model=e1000 -net 
> socket,vlan=0,connect=127.0.0.1:7000
> 
> The bandwidth is really tiny :
> 
>     . Iperf3 reports about 30 Mb/sec
>     . NetPerf reports about 50 Mb/sec
> 
> 
> With UDP sockets, there is no problem at all :
> 
>     . Iperf3 reports about 1 Gb/sec
>     . NetPerf reports about 950 Mb/sec
> 
> 
> I've noticed this fact only with the e1000 NIC, not with others 
> (rtl8139,virtio, etc.)
> I've used the main GIT version of QEMU.

It's interesting that you see good performance over -netdev socket TCP
with the other NIC models.

I don't know what the issue would be, you'll probably need to dig
further to discover the problem.  Using wireshark might be a good start.
Try to figure out where the delay is incurred and then instrument that
code to find out the cause.

Stefan