netdev - Re: UDP ordering when using multiple rx queue

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Date:	Wed, 11 Jul 2012 15:41:55 +0200
From:	Jean-Michel Hautbois <jhautbois@...il.com>
To:	Merav Sicron <meravs@...adcom.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: UDP ordering when using multiple rx queue

2012/7/11 Jean-Michel Hautbois <jhautbois@...il.com>:
> 2012/7/11 Merav Sicron <meravs@...adcom.com>:
>> On Wed, 2012-07-11 at 00:53 -0700, Jean-Michel Hautbois wrote:
>>
>>> Several tests lead to a simple conclusion : when the NIC has only one
>>> RX queue, everything is ok (like be2net for instance), but when it has
>>> more than one RX queue, then I can have "lost packets".
>>> This is the case for bnx2x or mlx4 for instance.
>> >From what you describe I assume that you use different source IP /
>> destination IP in each packet - is this something that you can control?
>> Because with the same IP addresses the traffic will be steered to the
>> same queue.
>
> OK, sorry for not having explained that : the packets are multicast
> with a port for each stream. Sending one stream multicast on a bnx2x
> based NIC can lead to several queues used (two, for what I can see)
> and then, to the problem reported.
>
>>> Here are my questions :
>>> - Is it possible to force a driver to use only one rx queue, even if
>>> it can use more without reloading the driver (and this is feasible
>>> only when a parameter exists for that !) ?
>> You can reduce the number of queues using "ethtool -L ethX combined 1".
>> Note however that it will cause automatic driver unload/load.
>
> OK, thanks for this tip :).
>
> JM

I confirm that using ethtool -L eth1 combined 1 solves my issue.
I can have 3Gbps per sec with 5 multicast on 5 ports without any
"packet loss" (again, for my application) and it uses one RX queue
only (of course :)).
One multicast (one port) but with the default combined=8 splits in two
rx queues...
Unicast traffic seems ok (I used netperf in order to check this assumption).

JM
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