linux-kernel - Re: questions on NAPI processing latency and dropped network packets

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Message-ID: <47866B8A.3040607@intel.com>
Date:	Thu, 10 Jan 2008 11:01:30 -0800
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Rick Jones <rick.jones2@...com>
CC:	Chris Friesen <cfriesen@...tel.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: questions on NAPI processing latency and dropped network packets

Rick Jones wrote:
>> 1) Interrupts are being processed on both cpus:
>>
>> root@...e0-0-0-13-0-11-1:/root> cat /proc/interrupts
>>            CPU0       CPU1
>>  30:    1703756    4530785  U3-MPIC Level     eth0
> 
> IIRC none of the e1000 driven cards are multi-queue

the pci-express variants are, but the functionality is almost always disabled (and
relatively new anyway).

even with multiqueue, you can still have only a single irq line (which defeats the
purpose of course mostly).

>, so while the above 
> shows that interrupts from eth0 have been processed on both CPUs at
> various points in the past, it doesn't necessarily mean that they are
> being processed on both CPUs at the same time right?

never will, an irq can only be processed on one cpu at a time anyway, obviously
the irq here has been migrated ONCE from one of the cpu's to the other.
unfortunately you can't see from /proc/interrupts whether this happens frequently
or not, or how many times it happened before.

Auke
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