netdev - Re: [PATCH net-next 0/2] sfc: enable 4-tuple UDP RSS hashing

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Date:   Tue, 8 Nov 2016 13:02:05 +0000
From:   Edward Cree <ecree@...arflare.com>
To:     David Miller <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <linux-net-drivers@...arflare.com>
Subject: Re: [PATCH net-next 0/2] sfc: enable 4-tuple UDP RSS hashing

On 07/11/16 18:20, David Miller wrote:
> From: Edward Cree <ecree@...arflare.com>
> Date: Thu, 3 Nov 2016 22:10:31 +0000
>
>> EF10 based NICs have configurable RSS hash fields, and can be made to take the
>> ports into the hash on UDP (they already do so for TCP).  This patch series
>> enables this, in order to improve spreading of UDP traffic.
> What does the chip do with fragmented traffic?
Only the first fragment will be considered UDP, it will treat the rest as "other
IP" and 2-tuple hash them, probably hitting a different queue.

My understanding is that while that will reduce performance, that shouldn't be a
problem as performance-sensitive users will avoid fragmentation anyway.
It could also lead to out-of-order packet delivery, but it's UDP so that's
supposed to be OK.