VM in Xen 4.1; poor packet forwarding performance on xn0

[seanrees at gmail.com]

On Sat, Apr 19, 2014 at 1:11 PM, Tiago Ribeiro <shasty at gmail.com> wrote:

>
>
> > Em 18/04/2014, às 11:57, "seanrees at gmail.com" <seanrees at gmail.com>
> escreveu:
> >
> > Hi there freebsd-xen,
> >
> > I tried first on freebsd-questions@ without success, so I thought to
> retry
> > here.
> >
> > I run OpenVPN on a FreeBSD 10.0-Rp1 VM in Xen 4.1 (HVM). I am
> experiencing
> > slow network performance on xn0 that seems to have developed after I
> > upgraded to FreeBSD 10 (no other changes). I can only achieve about
> 0.5mbps
> > through this interface when forwarding packets; packets in a single
> > direction are fine (e.g; downloading to the VPS or pushing from the VPS)
> > and clock in at many (>10 usually) mbps.
> >
> > Interestingly, my identical VM (configuration managed centrally) running
> on
> > Xen 3.4 (HVM) does *not* have this issue.
> >
> > I did a little debugging and here's what I've noticed:
> >   - Not related to OpenVPN, repro'd using ssh -d.
> >   - Slow VM has a very low rate of context switches (~250) while
> > forwarding, fast VM has a lot more (~2000) sampled over 5 seconds using
> > systat -v.
> >  - I can't repro a context switch limit (tried a limited fork() bomb).
> >  - Tried with *and* without LRO and TSO on xn0 (and all combinations of
> > LRO and TSO on/off)
> >
> > I started digging into the Xen drivers but I realised I am not equipped
> to
> > debug this. I'm looking for suggestions on what to check. My provider is
> > offering to move me to an older Xen host but I'd like to see if I can
> help
> > identify a bug either in my configuration or perhaps in FreeBSD's Xen
> code.
> >
> > Sean
> > _____________________________________________
>
>
> Do you use pf?


I do. Fairly simple ruleset: default deny, a few specific port allows, NAT.

Sean