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Date:      Tue, 11 Feb 2014 18:20:42 +0100
From:      =?UTF-8?B?Um9nZXIgUGF1IE1vbm7DqQ==?= <roger.pau@citrix.com>
To:        Karl Pielorz <kpielorz_lst@tdx.co.uk>, <freebsd-xen@freebsd.org>
Subject:   Re: Xen PV Networking issue - disable PV NIC in XENHVM FreeBSD?
Message-ID:  <52FA5BEA.6030307@citrix.com>
In-Reply-To: <72C34BC121BD5A0FBDAEFA37@Mail-PC.tdx.co.uk>
References:  <D280F84BE886E8D6110B93D0@study64.tdx.co.uk> <52F8FE87.1010705@citrix.com> <72C34BC121BD5A0FBDAEFA37@Mail-PC.tdx.co.uk>

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On 11/02/14 17:33, Karl Pielorz wrote:
> 
> 
> --On 10 February 2014 17:29 +0100 Roger Pau Monné <roger.pau@citrix.com>
> wrote:
> 
>> That's quite weird... Do you see any messages in the Xen console (xl
>> dmesg)? Can you boot with a hypervisor compiled with debug=y and see if
>> there are any strange messages on the Xen console?
> 
> Ok, no messages logged anywhere when this goes on - I'm running
> XenServer 6.2 installed from the distribution ISO (w/SP1 applied) - I
> don't know/think that's compiled with 'debug=y'? dmesg output for
> XenServer coming up is 'unremarkable' as far as I can see, and nothing
> is logged with 'xl dmesg'
> 
>> Also, does replacing the FreeBSD gateway VM with a Linux PV VM solve the
>> issue? (ie. just to check if Linux also shows this behaviour)
> 
> Ok, that I could do - and just did. I used CentOS 6 - which booted in
> 'Xen' aware mode (with Xen Virtual ethernet driver) - annoyingly that
> works *fine* (i.e. no issues).
> 
> So,
> 
>  Windows 7 PV <-> FreeBSD 9.x / 10.x PV = Fail (if on same XenServer host)
>  Windows 7 HVM <-> FreeBSD PV = Works
>  Windows 7 PV <-> Linux (CentOS 6) PV = Works

Just to clarify, are you unable to reach a FreeBSD PV DomU from a
Windows PV DomU on the same host, or are you unable to route traffic
trough a FreeBSD PV DomU (on the same host)?

(ie. can you ssh from the Windows PV DomU into the FreeBSD PV DomU?)

> 
> So it looks like it might actually be a FreeBSD/Xen issue?

Yes, it looks that way (dunno if netback might also be involved in this)

> I just tried booting FreeBSD 10 without the Xen options in the kernel,
> and it won't boot (it panics).
> 
> Is there any way of booting 10.x in HVM mode (i.e. with no Xen PV
> support) - or at least switching 'xn' for 're' as far as nic's go?

I have to look into this, FreeBSD should not panic when trying to boot
without XENHVM on a DomU.

AFAIK there's no way to selectively enable/disable the usage of certain
PV interfaces, but I certainly don't recommend switching to an emulated
nic to do the routing.

> Are there any 'offload' type features that can be disabled for 'xn' nics
> in FreeBSD?

You could try to disable the following:

ifconfig xnX -rxcsum -txcsum -tso4 -lro

Or a mix of those, I'm afraid I'm not that familiar with
netfront/netback to provide any more hints. In the past there have been
reports of TSO breaking on Xen PV interfaces, but AFAIK this should be
fixed already.

Roger.



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