netdev - Re: [PATCH RFC 1/3] xdp: Infrastructure to generalize XDP

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Date:   Wed, 21 Sep 2016 11:50:06 -0700
From:   Tom Herbert <tom@...bertland.com>
To:     Jakub Kicinski <kubakici@...pl>
Cc:     Alexei Starovoitov <ast@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Kernel Team <kernel-team@...com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Brenden Blanco <bblanco@...mgrid.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH RFC 1/3] xdp: Infrastructure to generalize XDP

On Wed, Sep 21, 2016 at 11:45 AM, Jakub Kicinski <kubakici@...pl> wrote:
> On Wed, 21 Sep 2016 10:39:40 -0700, Tom Herbert wrote:
>> On Wed, Sep 21, 2016 at 10:26 AM, Jakub Kicinski <kubakici@...pl> wrote:
>> > On Tue, 20 Sep 2016 17:01:39 -0700, Alexei Starovoitov wrote:
>> >>  >  - Reduces the amount of code and complexity needed in drivers to
>> >>  >    manage XDP
>> >>
>> >> hmm:
>> >> 534 insertions(+), 144 deletions(-)
>> >> looks like increase in complexity instead.
>> >
>> > and more to come to tie this with HW offloads.
>>
>> The amount of driver code did decrease with these patches:
>>
>> drivers/net/ethernet/mellanox/mlx4/en_netdev.c | 64 ++++----------------------
>> drivers/net/ethernet/mellanox/mlx4/en_rx.c     | 25 ++++------
>> drivers/net/ethernet/mellanox/mlx4/mlx4_en.h   |  1 -
>>
>> Minimizing complexity being added to drivers for XDP is critical since
>> we basically asking every driver to replicate the function. This
>> property also should also apply to HW offloads, the more complexity we
>> can abstract out drivers into a common backend infrastructure the
>> better for supporting across different drivers.
>
> I'm in the middle of writing/testing XDP support for the Netronome's
> driver and generic infra is very much appreciated ;)  In my experience
> the 50 lines of code which are required for assigning the programs and
> freeing them aren't really a big deal, though.
>

50 lines in one driver is not a big deal, 50 lines in a hundred
drivers is! I learned this lesson in BQL which was well abstracted out
to be minimally invasive but we still saw many issues because of the
pecularities of different drivers.

> Let's also separate putting xdp_prog in netdevice/napi_struct from the
> generic hook infra.  All the simplifications to the driver AFAICS come
> from the former.  If everyone is fine with growing napi_struct we can do
> that but IMHO this is not an argument for the generic infra :)