[Xen-devel] netfront/netback multiqueue exhausting grants

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

There have been a few reports recently[0] which relate to a failure of
netfront to allocate sufficient grant refs for all the queues:

[ÂÂÂÂ0.533589] xen_netfront: can't alloc rx grant refs
[ÂÂÂÂ0.533612] 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.

Ian.

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

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