[Xen-users] HVM PV (unmodified) driver performance

[Daire Byrne <Daire.Byrne@xxxxxxxxxxxxxxxxxx>]

Hi,

I have been testing the unmodified_drivers from the latest xen-unstable on my 
FC6 machine and I have a couple of questions regarding the results. It seems 
that I only get accelerated network performance in one direction namely sends 
from the HVM guest. I used iperf to benchmark performance between the HVM guest 
and the FC6 Dom0:

# HVM - No PV drivers #
Sends:
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0- 8.2 sec  17.8 MBytes  18.3 Mbits/sec

Receive:
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  54.9 MBytes  46.0 Mbits/sec

# HVM - with PV net driver #
Sends:
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec   788 MBytes   660 Mbits/sec

Receives
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  8.52 MBytes  7.13 Mbits/sec

As you can see the PV driver improves network performance when sending from the 
HVM guest (FC6 - 2.6.18) but if anything the receive/read performance is worse 
than when using the ioemu rtl1839 driver. Is this expected behaviour? Does it 
matter that I'm running xen-3.0.3 but using the xen-unstable umodified_drivers 
source? xen-unstable has support for building against the 2.6.18 kernel whereas 
3.0.3 does not. Is this message on start-up normal?: "netfront: device eth1 has 
copying recieve path". From what I've read the PV drivers for Linux should 
accelerate performance in both directions....

Here's my vif config line:
  vif = [ 'bridge=xenbr0' , 'type=ioemu, bridge=xenbr0' ]

I boot a "diskless" FC6 image from the network using pxe (etherboot for the 
rtl1839) and then load the unmodifed_drivers modules and bring up the network 
on eth1 (eth0 being the ioemu rtl1839). Am I doing anything wrong or is this 
expected behaviour? As an aside I tried building the unmodified_drivers against 
the FC3 2.6.12 kernel but they just hang on loading "xenbus.ko" - another known 
issue?

Any help or hints greatly appreciated!

Regards,

Daire

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