Re: netfront/netback multiqueue exhausting grants

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 01/20/2016 07:23 AM, Ian Campbell wrote:
> There have been a few reports recently[0] which relate to a failure of
> netfront to allocate sufficient grant refs for all the queues:
>
> [    0.533589] xen_netfront: can't alloc rx grant refs
> [    0.533612] net eth0: only created 31 queues
>
> Which can be worked around by increasing the number of grants on the
> hypervisor command line or by limiting the number of queues permitted by
> either back or front using a module param (which was broken but is now
> fixed on both sides, but I'm not sure it has been backported everywhere
> such that it is a reliable thing to always tell users as a workaround).
>
> Is there any plan to do anything about the default/out of the box
> experience? Either limiting the number of queues or making both ends cope
> more gracefully with failure to create some queues (or both) might be
> sufficient?
>
> I think the crash after the above in the first link at [0] is fixed? I
> think that was the purpose of ca88ea1247df "xen-netfront: update num_queues
> to real created" which was in 4.3.

I think ca88ea1247df is the solution --- it will limit the number of 
queues.

And apparently it's not in stable trees. At least not in 4.1.15, which 
is what the first reported is running:

https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/log/drivers/net/xen-netfront.c?id=refs/tags/v4.1.15

-boris


>
> Ian.
>
> [0] http://lists.xen.org/archives/html/xen-users/2016-01/msg00100.html
>      http://lists.xen.org/archives/html/xen-users/2016-01/msg00072.html
>      some before hte xmas break too IIRC