netdev - Re: [xdp-hints] Re: [PATCH bpf-next v7 15/17] net/mlx5e: Introduce wrapper for xdp

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Date:   Thu, 12 Jan 2023 23:29:58 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Tariq Toukan <ttoukan.linux@...il.com>, 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>,
        Saeed Mahameed <saeedm@...dia.com>,
        David Ahern <dsahern@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        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 v7 15/17] net/mlx5e: Introduce
 wrapper for xdp_buff

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

> On Thu, Jan 12, 2023 at 1:55 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>>
>> Toke Høiland-Jørgensen <toke@...hat.com> writes:
>>
>> > Stanislav Fomichev <sdf@...gle.com> writes:
>> >
>> >> On Thu, Jan 12, 2023 at 12:07 AM Tariq Toukan <ttoukan.linux@...il.com> wrote:
>> >>>
>> >>>
>> >>>
>> >>> On 12/01/2023 2:32, Stanislav Fomichev wrote:
>> >>> > From: Toke Høiland-Jørgensen <toke@...hat.com>
>> >>> >
>> >>> > Preparation for implementing HW metadata kfuncs. No functional change.
>> >>> >
>> >>> > Cc: Tariq Toukan <tariqt@...dia.com>
>> >>> > Cc: Saeed Mahameed <saeedm@...dia.com>
>> >>> > Cc: John Fastabend <john.fastabend@...il.com>
>> >>> > Cc: David Ahern <dsahern@...il.com>
>> >>> > Cc: Martin KaFai Lau <martin.lau@...ux.dev>
>> >>> > Cc: Jakub Kicinski <kuba@...nel.org>
>> >>> > Cc: Willem de Bruijn <willemb@...gle.com>
>> >>> > Cc: Jesper Dangaard Brouer <brouer@...hat.com>
>> >>> > Cc: Anatoly Burakov <anatoly.burakov@...el.com>
>> >>> > Cc: Alexander Lobakin <alexandr.lobakin@...el.com>
>> >>> > Cc: Magnus Karlsson <magnus.karlsson@...il.com>
>> >>> > Cc: Maryam Tahhan <mtahhan@...hat.com>
>> >>> > Cc: xdp-hints@...-project.net
>> >>> > Cc: netdev@...r.kernel.org
>> >>> > Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>> >>> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
>> >>> > ---
>> >>> >   drivers/net/ethernet/mellanox/mlx5/core/en.h  |  1 +
>> >>> >   .../net/ethernet/mellanox/mlx5/core/en/xdp.c  |  3 +-
>> >>> >   .../net/ethernet/mellanox/mlx5/core/en/xdp.h  |  6 +-
>> >>> >   .../ethernet/mellanox/mlx5/core/en/xsk/rx.c   | 25 ++++----
>> >>> >   .../net/ethernet/mellanox/mlx5/core/en_rx.c   | 58 +++++++++----------
>> >>> >   5 files changed, 50 insertions(+), 43 deletions(-)
>> >>> >
>> >>> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en.h b/drivers/net/ethernet/mellanox/mlx5/core/en.h
>> >>> > index 2d77fb8a8a01..af663978d1b4 100644
>> >>> > --- a/drivers/net/ethernet/mellanox/mlx5/core/en.h
>> >>> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en.h
>> >>> > @@ -469,6 +469,7 @@ struct mlx5e_txqsq {
>> >>> >   union mlx5e_alloc_unit {
>> >>> >       struct page *page;
>> >>> >       struct xdp_buff *xsk;
>> >>> > +     struct mlx5e_xdp_buff *mxbuf;
>> >>>
>> >>> In XSK files below you mix usage of both alloc_units[page_idx].mxbuf and
>> >>> alloc_units[page_idx].xsk, while both fields share the memory of a union.
>> >>>
>> >>> As struct mlx5e_xdp_buff wraps struct xdp_buff, I think that you just
>> >>> need to change the existing xsk field type from struct xdp_buff *xsk
>> >>> into struct mlx5e_xdp_buff *xsk and align the usage.
>> >>
>> >> Hmmm, good point. I'm actually not sure how it works currently.
>> >> mlx5e_alloc_unit.mxbuf doesn't seem to be initialized anywhere? Toke,
>> >> am I missing something?
>> >
>> > It's initialised piecemeal in different places; but yeah, we're mixing
>> > things a bit...
>> >
>> >> I'm thinking about something like this:
>
> Seems more invasive? I don't care much tbf, but what's wrong with
> keeping 'xdp_buff xsk' member and use it consistently?

Yeah, it's more invasive, but it's also more consistent with the non-xsk
path where every usage of struct xdp_buff is replaced with the wrapping
struct?

Both will work, I suppose (in fact I think the resulting code will be
more or less identical), so it's more a matter of which one is easier to
read and where we put the type-safety-breaking casts.

I can live with either one (just note you'll have to move the
'mxbuf->rq' initialisation next to the one for mxbuf->cqe for yours, but
that's probably fine too). Let's see which way Tariq prefers...

-Toke