Re: [Xen-users] VM bridge doesn't pass traffic

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2016-01-19 at 09:25 +0100, David Winterstein wrote:
> > > > > Lastly while I'm fishing for potential clues please could you
> > > > > post the
> > > > > output of of "xl -vvv create <cfg>", the -vvv makes it much more
> > > > > verbose.
> > > > Output of the create command: http://pastebin.com/7CqdS2Zd
> > > > Output of the vm boot process (from xl console):
> > > > http://pastebin.com/ZduwSmNn
> > > Ah, here is something interesting:
> > > 
> > > [ÂÂÂÂ1.507834] xen_netfront: Initialising Xen virtual ethernet driver
> > > [ÂÂÂÂ1.513754] xen_netfront: can't alloc rx grant refs
> > > [ÂÂÂÂ1.513762] net eth0: only created 32 queues
> > > 
> > > If you use fewer vcpus (like 2 for example) does it work? If so then
> > > a
> > > workaround would be to limit the number of queues to fewer than the
> > > number
> > > of vcpus (the default). IIRC there were some bugs in this capability,
> > > I'm
> > > hoping that Wei (cc-d) can remember the necessary dance.
> > > 
> > > An alternative to limiting the queues might be to increase the
> > > maximum
> > > number of pages each guest can use for grant tables (i.e. increase
> > > the
> > > number of grants). This can be done with the gnttab_max_nr_frames
> > > hypervisor command line option. (See http://xenbits.xen.org/docs/4.4/
> > > misc/x
> > > en-command-line.html).
> > > 
> > > I think the default is 32, so you could e.g. try doubling it.
> > Hell yes! It worked! Thank you so much!
> > Wish you all the best and have a nice week.
> 
> Haha, gotta take out some of the enthusiasm - the link you provided
> doesn't seem to work (404).

Sorry, I edited it from unstable to match your use of 4.4, but missed the
-testing suffix. Correct URL is:

http://xenbits.xen.org/docs/4.4-testing/misc/xen-command-line.html

> Googling for "gnttab_max_nr_frames" showed up that the term is probably
> deprecated and "max_grant_frames" should be used instead.

It wasn't deprecated yet in 4.4, looks like that happened in 4.5.

> I can't find how to apply the option, though. Where do I have to declare
> the variable? In /etc/default/xen or maybe /etc/xen/xl.conf or even the
> vm config file (though that wouldn't make any sense to me)?

It needs to go on the hypervisor command line.

Assuming you are using grub with the usual /etc/grub.d/20_linux_xen then
you can add a line to /etc/default/grub:
GRUB_CMDLINE_XEN="gnttab..."
and re-run update-grub (paths may differ on your distro).

The docs for this stuff are pretty much non-existent (there's some on the
Serial console and PCI passthrough wiki pages, but nothing generic which I
can see). I've added an entry toÂhttp://wiki.xenproject.org/wiki/Xen_Docume
nt_Days/TODO

> 
> Thanks in advance and kind regards,
> Â David
> 
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