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

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Date:	Thu, 31 May 2012 08:54:14 +0200
From:	Jean-Michel Hautbois <jhautbois@...il.com>
To:	Sathya.Perla@...lex.com
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org,
	yevgenyp@...lanox.com
Subject: Re: Difficulties to get 1Gbps on be2net ethernet card

2012/5/30  <Sathya.Perla@...lex.com>:
>>-----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

It seems this issue exist with mellanox mlx4 too...
I have a bond between eth1 (be2net) and eth9 (mlx4_en) and I can
switch from one to the other using ifenslave.
Setting a queue of 4000 on be2net works well in my use case, when I
switch to mlx4 based NIC which has a default queue len of 1000, I have
dropped packets too (less than be2net, but about 30-50 per second).
Setting a queue len of 4000 on mlx4 works too, but the number of
interrupts is similar.
The use case is the same : Lots of TX, no RX.

JM
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