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

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Date:	Sat, 30 Jun 2012 22:36:36 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:	davem@...emloft.net, Bruce Allan <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

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.

Ben.

-- 
Ben Hutchings
Lowery's Law:
             If it jams, force it. If it breaks, it needed replacing anyway.

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