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

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Date:	Wed, 19 Jan 2011 21:28:23 +0200
From:	Pasi Kärkkäinen <pasik@....fi>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	Ian Campbell <Ian.Campbell@...citrix.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	xen-devel <xen-devel@...ts.xensource.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [Xen-devel] Re: [PATCH] xen network backend driver

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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