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

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Message-ID: <1368633836.6796.1.camel@LTIRV-MCHAN1.corp.ad.broadcom.com>
Date:	Wed, 15 May 2013 09:03:56 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"Ben Hutchings" <bhutchings@...arflare.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 16:52 +0100, Ben Hutchings wrote: 
> 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.

Yes, tg3 hardware (may be all Broadcom hardware) can only use MSI as a
replacement for INTA.


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