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Re: [Xen-devel] Re: [PATCH] xen network backend driver

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] xen network backend driver
From: Pasi Kärkkäinen <pasik@xxxxxx>
Date: Wed, 19 Jan 2011 21:28:23 +0200
Cc: Ben Hutchings <bhutchings@xxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, "netdev@xxxxxxxxxxxxxxx" <netdev@xxxxxxxxxxxxxxx>
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On Wed, Jan 19, 2011 at 11:16:59AM -0800, Jeremy Fitzhardinge wrote:
> On 01/19/2011 10:05 AM, Ben Hutchings wrote:
> > Not in itself.  NAPI polling will run on the same CPU which scheduled it
> > (so wherever the IRQ was initially handled).  If the protocol used
> > between netfront and netback doesn't support RSS then RPS
> > <http://lwn.net/Articles/362339/> can be used to spread the RX work
> > across CPUs.
> There's only one irq per netback which is bound to one (V)CPU at a
> time.  I guess we could extend it to have multiple irqs per netback and
> some way of distributing packet flows over them, but that would only
> really make sense if there's a single interface with much more traffic
> than the others; otherwise the interrupts should be fairly well
> distributed (assuming that the different netback irqs are routed to
> different cpus).

Does "multiqueue" only work for NIC drivers (and frontend drivers),
or could it be used also for netback?

(afaik Linux multiqueue enables setting up multiple receive queues each having 
a separate irq.)

-- Pasi

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