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

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Message-ID: <4BF2C049.1080901@ans.pl>
Date:	Tue, 18 May 2010 18:28:57 +0200
From:	Krzysztof Olędzki <ole@....pl>
To:	Michael Chan <mchan@...adcom.com>
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 2010-05-18 04:11, Michael Chan wrote:
>
> 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.

Thanks again for the explanation.

Best regards,

			Krzysztof Olędzki
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