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Re: [Xen-users] Maximun number of NICs in PV?

On Thu, 2015-05-21 at 12:00 -0300, Pablo E. Bullian wrote:
> On 15/05/15 16:38, Pablo E. Bullian wrote:
> > Hi all, I'm looking for information regarding the maximum number of
> > network interfaces that a PV can have.
> > 
> > I need to create a PV (VyOS - it's a debian), with more than 15
> > NICs, but when I try to add more,  I get:
> > 
> > [    0.209088] xen_netfront: can't alloc rx grant refs
> > [    0.209268] vif vif-15: 12 creating netdev
> > [    0.212789] vif vif-15: failed to write error node for
> > device/vif/15 (12 creating netdev)
> > [    0.214610] vif vif-15: 12 xenbus_dev_probe on device/vif/15
> > [    0.215347] vif vif-15: failed to write error node for
> > device/vif/15 (12 xenbus_dev_probe on device/vif/15)

Poking around in the code a bit you could try using the max_queues
module parameter when loading netfront to set the queues to 1. My
hypothesis is that multiple queues over so many vifs are exhausting the
supply of grant refs faster than 2.6.16 which didn't do multi queue.

For expanding the number of grant refs available in general it looks
like you can pass gnttab_max_frames= as an option to the hypervisor when
booting. The default appears to be 32.

That will let all domains potentially consume a little more RAM (e.g.
increasing to 64 would allow the domain to use 2 extra megabytes for
grant table).


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