Re: [xdp-hints] Re: [PATCH bpf-next v2 6/8] mlx4: Introduce mlx4_xdp_buff wrapper for xdp_buff - Toke Høiland-Jørgensen

From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Stanislav Fomichev <sdf@google.com>
Cc: Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
	Jakub Kicinski <kuba@kernel.org>,
	bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
	andrii@kernel.org, martin.lau@linux.dev, song@kernel.org,
	yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org,
	haoluo@google.com, jolsa@kernel.org,
	Tariq Toukan <tariqt@nvidia.com>, David Ahern <dsahern@gmail.com>,
	Willem de Bruijn <willemb@google.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Anatoly Burakov <anatoly.burakov@intel.com>,
	Alexander Lobakin <alexandr.lobakin@intel.com>,
	Magnus Karlsson <magnus.karlsson@gmail.com>,
	Maryam Tahhan <mtahhan@redhat.com>,
	xdp-hints@xdp-project.net, netdev@vger.kernel.org
Subject: Re: [xdp-hints] Re: [PATCH bpf-next v2 6/8] mlx4: Introduce mlx4_xdp_buff wrapper for xdp_buff
Date: Mon, 28 Nov 2022 23:11:36 +0100	[thread overview]
Message-ID: <871qpm20h3.fsf@toke.dk> (raw)
In-Reply-To: <CAKH8qBvbYuCq-iiXnMw1QxFbfLFhorpF1+GGqU1yVzX2LhoUzQ@mail.gmail.com>

Stanislav Fomichev <sdf@google.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