netdev - Re: [xdp-hints] Re: [PATCH bpf-next v2 6/8] mlx4: Introduce mlx4_xdp_buff wrapper for xdp

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Date:   Mon, 28 Nov 2022 23:11:36 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jakub Kicinski <kuba@...nel.org>, bpf@...r.kernel.org,
        ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, haoluo@...gle.com,
        jolsa@...nel.org, Tariq Toukan <tariqt@...dia.com>,
        David Ahern <dsahern@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Anatoly Burakov <anatoly.burakov@...el.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
        netdev@...r.kernel.org
Subject: Re: [xdp-hints] Re: [PATCH bpf-next v2 6/8] mlx4: Introduce
 mlx4_xdp_buff wrapper for xdp_buff

Stanislav Fomichev <sdf@...gle.com> writes:

>> >> Why can't you simply have a pointer to xdp_buff in driver specific
>> >> xdp_buff container which would point to xdp_buff that is stack based (or
>> >> whatever else memory that will back it up - I am about to push a change
>> >> that makes ice driver embed xdp_buff within a struct that represents Rx
>> >> ring) for XDP path and for ZC the pointer to xdp_buff that you get from
>> >> xsk_buff_pool ? This would satisfy both sides I believe and would let us
>> >> keep the same container struct.
>> >>
>> >> struct mlx4_xdp_buff {
>> >>      struct xdp_buff *xdp;
>> >>      struct mlx4_cqe *cqe;
>> >>      struct mlx4_en_dev *mdev;
>> >>      struct mlx4_en_rx_ring *ring;
>> >>      struct net_device *dev;
>> >> };
>> >
>> > Nah this won't work from kfunc POV, probably no way to retrieve the
>> > mlx4_xdp_buff based on xdp_buff ptr that needs to be used as an arg.
>> >
>> > Sorry I'll think more about it, in the meantime let's hear more voices
>> > whether we should keep Stan's original approach + modify xdp_buff_xsk or
>> > go with Toke's proposal.
>>
>> OK, so I played around with the mlx5 code a bit more, and I think the
>> "wrapping struct + cb area" can be made to work without too many ugly
>> casts; I'll send an updated version of the mlx5 patches with this
>> incorporated tomorrow, after I've run some tests...
>
> I'll probably send a v3 sometime tomorrow (PST), so maybe wait for me
> to make sure we are working on the same base?
> Or LMK if you prefer to do it differently..

OK, I'll send you my mlx5 patches off-list so you can just incorporate
those. Got stuck on some annoying build issues for the perf testing, so
will defer that until your next version, then :)

-Toke