netdev - Re: bnx2/BCM5709: why 5 interrupts on a 4 core system (2.6.33.3)

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Date:	Mon, 17 May 2010 19:11:58 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"Krzysztof Olędzki" <ole@....pl>
cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: bnx2/BCM5709: why 5 interrupts on a 4 core system
 (2.6.33.3)


On Tue, 2010-05-18 at 08:35 -0700, Krzysztof Olędzki wrote:
> On 2010-05-16 20:51, Michael Chan wrote:
> > Krzysztof Oledzki wrote:
> >
> >>
> >> Why the driver registers 5 interrupts instead of 4? How to
> >> limit it to 4?
> >>
> >
> > The first vector (eth0-0) handles link interrupt and other slow
> > path events.  It also has an RX ring for non-IP packets that are
> > not hashed by the RSS hash.  The majority of the rx packets should
> > be hashed to the rx rings eth0-1 - eth0-4, so I would assign these
> > vectors to different CPUs.
> 
> Did some more test on a two 4 core CPUs (8 CPUs reported to the system) 
> and on a two 4 core CPUs with HT (16 CPUs reported to the system) and in 
> both cases there are 8 instead of 9 vectors: eth0-0 .. eth0-7 (irqs 61 
> .. 68). However, dmesg shows that 9 interrupts are allocated:
> 
> bnx2 0000:01:00.0: irq 61 for MSI/MSI-X
> bnx2 0000:01:00.0: irq 62 for MSI/MSI-X
> bnx2 0000:01:00.0: irq 63 for MSI/MSI-X
> bnx2 0000:01:00.0: irq 64 for MSI/MSI-X
> bnx2 0000:01:00.0: irq 65 for MSI/MSI-X
> bnx2 0000:01:00.0: irq 66 for MSI/MSI-X
> bnx2 0000:01:00.0: irq 67 for MSI/MSI-X
> bnx2 0000:01:00.0: irq 68 for MSI/MSI-X
> bnx2 0000:01:00.0: irq 69 for MSI/MSI-X
> 
> It such case, which ring will be used for slow path and non-IP packets 
> and why there is no additional queue like in a 4CPU case?
> 

eth0-0 is always the one handling slow path, rx ring 0 (non-IP), and tx
ring 0.  The last vector is not used by bnx2.  It is reserved for iSCSI
which is handled by the cnic and bnx2i drivers.


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