Poor network performance with Xen + OpenVPN?

[Karl Pielorz]

Hi All,

A while ago I ran into an issue with FreeBSD + Xen and networking (where 
FreeBSD PVHVM domU's can't "route" traffic to/from other domU's 
(fbsd/linux/windows) - e.g. as a default gateway).

I seem to have run into what appears to be another network issue now  - 
XenServer 6.5-SP1 +hotfixes, with FreeBSD 10.1-p4 (as PVHVM), and OpenVPN 
2.3.7

Everything 'works OK' - but the performance is pretty poor. Most noticeable 
- if you have a browser open fetching pages via the VPN - the pages arrive 
very slowly, and any ssh sessions etc. are instantly put on a 'go slow', 
you also start getting ping timeouts when pinging hosts the other side of 
the VM/VPN until the pages are fetched.

Swap back to a bare metal system (on the same networks) - it works fine, 
switch back over to the VM - and again, performance is lousy.

The host running OpenVPN isn't really under any load (it's only job is 
running OpenVPN) - nor is it's XenServer.

If I connect to another OpenVPN host which is running on an HVM FreeBSD 9.1 
domU - performance is indistinguishable from the bare metal (as you'd 
expect considering the relatively low volumes of traffic over the VPN etc.)

Can anyone suggest any fixes / where to look to try and keep it as PVHVM, 
and get the performance back? - as we've already got a collection of HVM 
machines (to work round the other network problem) - which I don't really 
want to add to, as they're not agile :(

Cheers,

-Karl