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

[David Winterstein <david.winterstein@xxxxxxxxxxxxxx>]

>>>>>> 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:
>>>>
>>>> [    1.507834] xen_netfront: Initialising Xen virtual ethernet driver
>>>> [    1.513754] xen_netfront: can't alloc rx grant refs
>>>> [    1.513762] 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

Ah yeah, found it. %)
No documentation on how to apply these options, though. Without you I'd
been completely lost.


>> 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.

"gnttab_max_nr_frames" is not only not deprecated yet but also
"max_grant_frames" seemingly isn't even implemented in 4.4?
At least it only works with the gnttab one for me.


>> 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).

Confirmed. After adding
GRUB_CMDLINE_XEN="gnttab_max_nr_frames=64"
to /etc/default/grub, running update-grub and rebooting the dom0 it
finally worked with all 32 CPUs.


> 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 to http://wiki.xenproject.org/wiki/Xen_Docume
> nt_Days/TODO

Looks good, should help some people in the future.

Thanks again for your help!
Regards,
  David


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