From owner-freebsd-virtualization@freebsd.org  Mon Feb 19 11:02:28 2018
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Date: Mon, 19 Feb 2018 11:02:19 +0000
From: Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>
To: Laurence Pawling <laurence.pawling@globalsign.com>
CC: "freebsd-xen@freebsd.org" <freebsd-xen@freebsd.org>,
 "freebsd-virtualization@freebsd.org" <freebsd-virtualization@freebsd.org>,
 "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, David King
 <david.king@globalsign.com>, Vlad Galu <vlad.galu@globalsign.com>
Subject: Re: multi-vCPU networking issues as client OS under Xen
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On Mon, Feb 19, 2018 at 10:42:08AM +0000, Laurence Pawling wrote:
> >    When using >1 vCPUs can you set hw.xn.num_queues=1 on
> >    /boot/loader.conf and try to reproduce the issue?
> >    
> >    I'm afraid this is rather related to multiqueue (which is only used
> >    if >1 vCPUs).
> >    
> >    Thanks, Roger.
> 
> Roger - thanks for your quick reply, this is confirmed. Setting hw.xn.num_queues=1 on the server VM when vCPUs > 1 prevents the issue.

I've also been told that in order to discard this being a XenServer
specific issue you should execute the following on Dom0 and reboot the
server:

# xe-switch-network-backend bridge

And then try to reproduce the issue again with >1 vCPUs (and of course
removing the queue limit in loader.conf)

> For reference, please can you comment on the performance impact of this?

I'm afraid I don't have any numbers.

Roger.