netdev - RE: Difficulties to get 1Gbps on be2net ethernet card

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Date:	Wed, 30 May 2012 03:04:50 -0700
From:	<Sathya.Perla@...lex.Com>
To:	<jhautbois@...il.com>, <eric.dumazet@...il.com>
CC:	<netdev@...r.kernel.org>
Subject: RE: Difficulties to get 1Gbps on be2net ethernet card

>-----Original Message-----
>From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org] On
>Behalf Of Jean-Michel Hautbois
>
>2012/5/30 Jean-Michel Hautbois <jhautbois@...il.com>:
>
>I used vmstat in order to see the differences between the two kernels.
>The main difference is the number of interrupts per second.
>I have an average of 87500 on 3.2 and 7500 on 2.6, 10 times lower !
>I suspect the be2net driver to be the main cause, and I checkes the
>/proc/interrupts file in order to be sure.
>
>I have for eth1-tx on 2.6.26 about 2200 interrupts per second and 23000 on 3.2.
>BTW, it is named eth1-q0 on 3.2 (and tx and rx are the same IRQ)
>whereas there is eth1-rx0 and eth1-tx on 2.6.26.

Yes, there is an issue with be2net interrupt mitigation in the recent code with
RX and TX on the same Evt-Q (commit 10ef9ab4). The high interrupt rate happens when a TX blast is
done while RX is relatively silent on a queue pair. Interrupt rate due to TX completions is not being
mitigated.

I have a fix and will send it out soon..

thanks,
-Sathya