netdev - Re: [net-next] e1000e: remove use of IP payload checksum

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Date:	Sat, 30 Jun 2012 17:37:52 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ben@...adent.org.uk
Cc:	jeffrey.t.kirsher@...el.com, bruce.w.allan@...el.com,
	netdev@...r.kernel.org, gospo@...hat.com, sassmann@...hat.com
Subject: Re: [net-next] e1000e: remove use of IP payload checksum

From: Ben Hutchings <ben@...adent.org.uk>
Date: Sat, 30 Jun 2012 22:36:36 +0100

> On Sat, 2012-06-30 at 03:35 -0700, Jeff Kirsher wrote:
>> From: Bruce Allan <bruce.w.allan@...el.com>
>> 
>> Currently only used when packet split mode is enabled with jumbo frames,
>> IP payload checksum (for fragmented UDP packets) is mutually exclusive with
>> receive hashing offload since the hardware uses the same space in the
>> receive descriptor for the hardware-provided packet checksum and the RSS
>> hash, respectively.  Users currently must disable jumbos when receive
>> hashing offload is enabled, or vice versa, because of this incompatibility.
>> Since testing has shown that IP payload checksum does not provide any real
>> benefit, just remove it so that there is no longer a choice between jumbos
>> or receive hashing offload but not both as done in other Intel GbE drivers
>> (e.g. e1000, igb).
>> 
>> Also, add a missing check for IP checksum error reported by the hardware;
>> let the stack verify the checksum when this happens.
> [...]
> 
> The change to enable RX hashing in 3.4, with this odd restriction seems
> to have broken most existing systems using jumbo MTU on e1000e.  None of
> the distro scripts or network management daemons will automatically
> change offload configuration before MTU; how could they know?
> 
> Therefore this needs to be fixed in 3.5 and 3.4.y, not net-next.

Agreed.
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