misc. questions

[Colin Percival]

On 03/06/13 12:17, Jay West wrote:
> 1)            One or two of our freebsd 9.1 HVM (with PVM drivers) under
> Xenserver 6.1 advanced are fairly frequently generating this message on the
> console: xn_txeof: WARNING: response is -1! Any ideas what this may be and
> what should be done? It does seem to only occur on the machines that have
> higher network load than the others.

I see this on EC2 (running under HVM) as well.  It doesn't seem to interfere
with anything and only occurs occasionally (maybe five times per GB of network
traffic?) so I haven't worried too much about it -- but if anyone has a clue
about this I'd love to fix it from the "tidy up loose ends" perspective.

> 2)            We did a pilot project of about 8 VM's (the above mentioned
> environment) and all went well. Now that we've moved it into production with
> many more VM's, I'm wondering about recommended tuning. I seem to recall
> from watching this list that there are a few sysctl's and the like that are
> highly recommended, I think they had to do with network settings and turning
> off "offloading" or somesuch. Does anyone have a quick & dirty list of
> "here's the first things you should always change" with regards to FreeBSD
> HVM (pvm drivers) under XenServer?

You'll want to turn off tso, since it produces long mbuf chains which most
xn netbacks choke on.  (I have a very ugly workaround patch for this which I
use on EC2, but simply turning off tso is enough unless you need Gbps+ speeds).

There's a separate issue affecting pf+tso+xn (possibly pf+tso generally) which
I haven't gotten around to tracking down.

-- 
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid