netdev - Re: [PATCH net 1/3] vlan: Fix tcp checksums offloads for Q-in-Q vlan.

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Message-ID: <35dc2a59-7e6b-224d-49da-085d3f140fe7@redhat.com>
Date:   Tue, 23 May 2017 08:59:45 -0400
From:   Vlad Yasevich <vyasevic@...hat.com>
To:     David Miller <davem@...emloft.net>, vyasevich@...il.com
Cc:     netdev@...r.kernel.org, makita.toshiaki@....ntt.co.jp
Subject: Re: [PATCH net 1/3] vlan: Fix tcp checksums offloads for Q-in-Q vlan.

On 05/22/2017 07:59 PM, David Miller wrote:
> From: Vladislav Yasevich <vyasevich@...il.com>
> Date: Thu, 18 May 2017 09:31:03 -0400
> 
>> It appears that since commit 8cb65d000, Q-in-Q vlans have been
>> broken.  The series that commit is part of enabled TSO and checksum
>> offloading on Q-in-Q vlans.  However, most HW we support can't handle
>> it.  To work around the issue, the above commit added a function that
>> turns off offloads on Q-in-Q devices, but it left the checksum offload.
>> That will cause issues with most older devices that supprort very basic
>> checksum offload capabilities as well as some newer devices (we've
>> reproduced te problem with both be2net and bnx).
>>
>> To solve this for everyone, turn off checksum offloading feature
>> by default when sending Q-in-Q traffic.  Devices that are proven to
>> work can provided a corrected ndo_features_check implemetation.
>>
>> Fixes: 8cb65d000 ("net: Move check for multiple vlans to drivers")
>> CC: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
>> Signed-off-by: Vladislav Yasevich <vyasevic@...hat.com>
> 
> This is a tough one.  I can certainly sympathize with your frustration
> trying to track this down.
> 
> Clearing NETIF_F_HW_CSUM completely is the most conservative change.
> 
> However, for all the (perhaps many) cards upon which the checksumming
> does work properly in Q-in-Q situations, this change could be
> introducing non-trivial performance regressions.
> 
> So I think Toshiaki's suggestion to drop IP_CSUM and IPV6_CSUM is,
> on balance, the best way forward.
> 

Thanks.  I'll update and re-submit.

-vlad

> Thanks.
>