netdev - Re: BCM5719(tg3) use multiple MSI with RSS

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Message-ID: <1368633120.2652.11.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Wed, 15 May 2013 16:52:00 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Michael Chan <mchan@...adcom.com>
CC:	Mike Qiu <qiudayu@...ux.vnet.ibm.com>, <eilong@...adcom.com>,
	<mcarlson@...adcom.com>, <zambrano@...adcom.com>,
	<jeffrey.t.kirsher@...el.com>, <netdev@...r.kernel.org>
Subject: Re: BCM5719(tg3) use multiple MSI with RSS

On Wed, 2013-05-15 at 08:08 -0700, Michael Chan wrote:
> On Wed, 2013-05-15 at 15:56 +0800, Mike Qiu wrote: 
> > Hi all
> > 
> > Currently, I need to enable multiple MSI on BCM5719 network card.
> > But I look in to the spec of 5719 from Broadcom, it seems
> > that RSS just enable with MSI-X, so I'm not sure if multiple
> > MSI can use RSS.
> > 
> 
> MSI can only support one IRQ source and cannot support RSS.

It is possible for an MSI capability to have multiple MSIs, but they
will use the same address and consecutive data values.

On x86, if you can find a large enough block of free IRQs on an IOAPIC,
it is possible to implement RSS this way.  Linux supports this on
systems with an x2apic.

Now, maybe tg3 hardware doesn't support this (and really, why bother
when there is MSI-X?) but the option does exist.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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