netdev - Re: [E1000-devel] behaviour question for igb on nehalem box

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Message-ID: <alpine.WNT.2.00.0910161544330.13364@jbrandeb-mobl2.amr.corp.intel.com>
Date:	Fri, 16 Oct 2009 15:48:18 -0700 (Pacific Daylight Time)
From:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
To:	Richard Scobie <richard@...ce.co.nz>
cc:	Chris Friesen <cfriesen@...tel.com>,
	e1000-list <e1000-devel@...ts.sourceforge.net>,
	Linux Network Development list <netdev@...r.kernel.org>,
	"Allan, Bruce W" <bruce.w.allan@...el.com>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"gospo@...hat.com" <gospo@...hat.com>
Subject: Re: [E1000-devel] behaviour question for igb on nehalem box

On Fri, 16 Oct 2009, Richard Scobie wrote:
> I'm have just put together a Nehalem system (1 x Xeon), 
> 2.6.30.8-64.fc11.x86_64, which has quad onboard 82576 and noticed during 
> testing using just a single interface, that the RX queues on the other 3 
> were receiving interrupts - observed in /proc/interrupts.
> 
> Is this normal behaviour?

Hi Richard, 

This is normal, since we trigger an interrupt on every queue during our 
watchdog.  So if the interface is up it should be triggering an interrupt 
on every queue every two seconds.

This has (and will probably continue to be) necessary in order to pick up 
any straggler packets due to any (extremely rare, but expected to occur) 
missed interrupts that could happen when traffic is running.  It also is 
extremely useful if you're doing irq affinitization and/or debugging 
interrupts.

you can bring down the interfaces and they will stop interrupting.

Jesse
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