netdev - Re: [PATCH bpf V7 3/7] xdp: rss hash types representation

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Date:   Mon, 10 Apr 2023 17:04:02 +0200
From:   Simon Horman <simon.horman@...igine.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     bpf@...r.kernel.org, Stanislav Fomichev <sdf@...gle.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        martin.lau@...nel.org, ast@...nel.org, daniel@...earbox.net,
        alexandr.lobakin@...el.com, larysa.zaremba@...el.com,
        xdp-hints@...-project.net, anthony.l.nguyen@...el.com,
        yoong.siang.song@...el.com, boon.leong.ong@...el.com,
        intel-wired-lan@...ts.osuosl.org, pabeni@...hat.com,
        jesse.brandeburg@...el.com, kuba@...nel.org, edumazet@...gle.com,
        john.fastabend@...il.com, hawk@...nel.org, davem@...emloft.net,
        tariqt@...dia.com, saeedm@...dia.com, leon@...nel.org,
        linux-rdma@...r.kernel.org
Subject: Re: [PATCH bpf V7 3/7] xdp: rss hash types representation

On Sat, Apr 08, 2023 at 09:24:51PM +0200, Jesper Dangaard Brouer wrote:
> The RSS hash type specifies what portion of packet data NIC hardware used
> when calculating RSS hash value. The RSS types are focused on Internet
> traffic protocols at OSI layers L3 and L4. L2 (e.g. ARP) often get hash
> value zero and no RSS type. For L3 focused on IPv4 vs. IPv6, and L4
> primarily TCP vs UDP, but some hardware supports SCTP.
> 
> Hardware RSS types are differently encoded for each hardware NIC. Most
> hardware represent RSS hash type as a number. Determining L3 vs L4 often
> requires a mapping table as there often isn't a pattern or sorting
> according to ISO layer.
> 
> The patch introduce a XDP RSS hash type (enum xdp_rss_hash_type) that
> contain combinations to be used by drivers, which gets build up with bits
> from enum xdp_rss_type_bits. Both enum xdp_rss_type_bits and
> xdp_rss_hash_type get exposed to BPF via BTF, and it is up to the
> BPF-programmer to match using these defines.
> 
> This proposal change the kfunc API bpf_xdp_metadata_rx_hash() adding
> a pointer value argument for provide the RSS hash type.
> 
> Change function signature for all xmo_rx_hash calls in drivers to make it
> compile. The RSS type implementations for each driver comes as separate
> patches.
> 
> Fixes: 3d76a4d3d4e5 ("bpf: XDP metadata RX kfuncs")
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Acked-by: Toke Høiland-Jørgensen <toke@...hat.com>
> Acked-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>  drivers/net/ethernet/mellanox/mlx4/en_rx.c       |    3 +
>  drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c |    3 +
>  drivers/net/veth.c                               |    3 +
>  include/linux/netdevice.h                        |    3 +
>  include/net/xdp.h                                |   45 ++++++++++++++++++++++
>  net/core/xdp.c                                   |   10 ++++-
>  6 files changed, 62 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> index 4b5e459b6d49..73d10aa4c503 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> @@ -681,7 +681,8 @@ int mlx4_en_xdp_rx_timestamp(const struct xdp_md *ctx, u64 *timestamp)
>  	return 0;
>  }
>  
> -int mlx4_en_xdp_rx_hash(const struct xdp_md *ctx, u32 *hash)
> +int mlx4_en_xdp_rx_hash(const struct xdp_md *ctx, u32 *hash,
> +			enum xdp_rss_hash_type *rss_type)
>  {
>  	struct mlx4_en_xdp_buff *_ctx = (void *)ctx;
>  

Hi Jesper,

I think you also need to update the declaration of mlx4_en_xdp_rx_hash()
in mlx4_en.h.

...