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Re: [Xen-devel] netfront/netback multiqueue exhausting grants

On 2016/1/20 7:23, 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).
Following are the patches to fix module param, they exist since v4.3.
xen-netfront: respect user provided max_queues
xen-netback: respect user provided max_queues

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
We run into similar issue recently, and guess it is better to suggest user to set netback module parameter with the default value as 8? see this link, http://wiki.xenproject.org/wiki/Xen-netback_and_xen-netfront_multi-queue_performance_testing
Probably more test are needed to get the default number of best experience.

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.



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

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