netdev - Re: [PATCH net] netdevice.h: Fix unintentional disable of ALL_FOR

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Date:   Thu, 26 Nov 2020 14:01:07 +0200
From:   Tariq Toukan <ttoukan.linux@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Tariq Toukan <tariqt@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Moshe Shemesh <moshe@...dia.com>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH net] netdevice.h: Fix unintentional disable of ALL_FOR_ALL
 features on upper device



On 11/25/2020 11:27 AM, Eric Dumazet wrote:
> On Wed, Nov 25, 2020 at 10:06 AM Tariq Toukan <ttoukan.linux@...il.com> wrote:
>>
>>
>>
>> On 11/25/2020 5:25 AM, Herbert Xu wrote:
>>> On Tue, Nov 24, 2020 at 11:48:35AM +0100, Eric Dumazet wrote:
>>>>
>>>> Well, the 'increment' part was suggesting the function was adding
>>>> flags, not removing them.
>>>
>>> The idea of the increment part is that we're adding a constituent
>>> device, not that we're adding features.  There have always been
>>> features which were conjunctions, i.e., they must be supported by
>>> all underlying devices for them to be enabled on the virtual device.
>>>
>>> Your use of the increment function is unusual, as you're not adding
>>> features that belong to one underlying device, but rather you're
>>> trying to enable a feature on the virtual device unconditionally.
> 
> This was not the intent.
> 
> We can still disable TSO on the bonding device if desired.
> 
> pk51:~# for i in bond0 eth1 eth2; do ethtool -k $i|grep
> tcp-segmentation-offload; done
> tcp-segmentation-offload: on
> tcp-segmentation-offload: on
> tcp-segmentation-offload: on
> lpk51:~# ethtool -K bond0 tso off
> Actual changes:
> tcp-segmentation-offload: off
> tx-tcp-segmentation: off
> tx-tcp-ecn-segmentation: off
> tx-tcp-mangleid-segmentation: off
> tx-tcp6-segmentation: off
> large-receive-offload: off [requested on]
> lpk51:~# for i in bond0 eth1 eth2; do ethtool -k $i|grep
> tcp-segmentation-offload; done
> tcp-segmentation-offload: off
> tcp-segmentation-offload: on
> tcp-segmentation-offload: on
> 
> The intent was that we could have :
> 
> lpk51:~# ethtool -K bond0 tso on
> Actual changes:
> tcp-segmentation-offload: on
> tx-tcp-segmentation: on
> tx-tcp-ecn-segmentation: on
> tx-tcp-mangleid-segmentation: on
> tx-tcp6-segmentation: on
> lpk51:~# ethtool -K eth1 tso off
> lpk51:~# ethtool -K eth2 tso off
> lpk51:~# for i in bond0 eth1 eth2; do ethtool -k $i|grep
> tcp-segmentation-offload; done
> tcp-segmentation-offload: on
> tcp-segmentation-offload: off
> tcp-segmentation-offload: off
> lpk51:~#
> 
> 

IIUC, we want to let the bond TSO feature bit be totally independent, 
not affected by slaves.
If so, I think that:
First we should take NETIF_F_GSO_SOFTWARE (or just NETIF_F_ALL_TSO) out 
of NETIF_F_ONE_FOR_ALL.
Then, make sure it is set in bond_setup (it is already done, as part of 
BOND_VLAN_FEATURES).

I think this new logic is good for all other upper devices, which will 
be affected by the change in NETIF_F_ONE_FOR_ALL.


>>>
>>>> We might ask Herbert Xu if we :
>>>>
>>>> 1) Need to comment the function, or change its name to be more descriptive.
>>>> 2) Change the behavior (as you suggested)
>>>> 3) Other choice.
>>>
>>> I think Tariq's patch is fine, although a comment should be added
>>> to netdev_add_tso_features as this use of the increment function
>>> is nonstandard.
>>>
>>
>> Thanks Herbert, I'll add a comment and re-spin.
> 
> I think we should remove the use of  netdev_increment_features() and
> replace it with something else,
> because there is too much confusion.
> 

I think it would be best.

I can prepare the patch I described above if you agree with it.