Re: [PATCH net] xen-netback: bookkeep number of queues in our own module

From: Paul Durrant <redacted>
Date: Mon, 23 Jun 2014 07:59:16 +0000

Bear in mind that the original intention of the multi-queue patches
was to allow the queue selection algorithm to be negotiated with the
frontend (see
http://lists.xen.org/archives/html/xen-devel/2013-06/msg02654.html). Particularly,
if the frontend is Windows then netback will need to use a Toeplitz
hash to steer traffic since this is stipulated by Microsoft's RSS
(Receive Side Scaling) interfaces. So, IMO netback should always
implement a select queue method, otherwise any (theoretical)
algorithm change in __netdev_pick_tx() would be immediately imposed
on frontends, possibly causing them to misbehave.

I do not think you are obligated to use Toeplitz or whatever scheme
the other side wants, especially if the user on the xen-netback side
asked for XPS or similar to be used.