netdev - Re: [PATCH net-next 1/4] net: Introduce NETIF_F_GRO

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Date:   Mon, 4 Dec 2017 10:23:03 -0800
From:   Michael Chan <michael.chan@...adcom.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        Ariel Elior <Ariel.Elior@...ium.com>,
        everest-linux-l2@...ium.com
Subject: Re: [PATCH net-next 1/4] net: Introduce NETIF_F_GRO_HW

On Mon, Dec 4, 2017 at 8:47 AM, Alexander Duyck
<alexander.duyck@...il.com> wrote:
> On Mon, Dec 4, 2017 at 3:12 AM, Michael Chan <michael.chan@...adcom.com> wrote:
>> Introduce NETIF_F_GRO_HW feature flag for NICs that support hardware
>> GRO.  With this flag, we can now independently turn on or off hardware
>> GRO when GRO is on.  Hardware GRO guarantees that packets can be
>> re-segmented by TSO/GSO to reconstruct the original packet stream.
>>
>> Cc: Ariel Elior <Ariel.Elior@...ium.com>
>> Cc: everest-linux-l2@...ium.com
>> Signed-off-by: Michael Chan <michael.chan@...adcom.com>
>
> Do we really need yet another feature bit for this? We already have
> LRO and GRO and now we have to add something that isn't quite either
> one?

I think so, to be consistent with TSO/GSO on the transmit side.  On
the receive side, we have LRO/GRO_HW/GRO.  There is difference between
LRO/GRO_HW that we need to distinguish between the 2.

>
> I think I would rather have something like a netdev private flag that
> says LRO assembled frames are routable and just have this all run over
> the LRO flag with a test for the private flag to avoid triggering the
> LRO disable in the case of the flag being present. Really this is just
> a clean LRO implementation anyway so maybe we should just go that
> route where LRO is the hardware offload and GRO is the generic
> software implementation of that offload. That way when GRO gets some
> new feature that your hardware doesn't support we don't have to argue
> about the differences since LRO is meant to be a limited
> implementation anyway due to the nature of it being in hardware.

Private flag will work.  But a standard feature flag is better since
there are multiple drivers supporting this.  A standard way to turn
this on/off is a better user experience.  It's also consistent with
TSO/GSO on the transmit side.

>
> To me it just seems like this is an attempt to use the GRO name as a
> marketing term and I really don't like the feel of it.
>

I disagree with this.  It's more than a marketing term.