netdev - Re: [PATCH net-next] net/mlx4_en: CHECKSUM

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Message-ID: <CALzJLG-BEORd+YgBqk1E1PFd8fjzDkUDQGP29ApgMaQXTPJxqw@mail.gmail.com>
Date:   Thu, 29 Mar 2018 17:34:14 -0700
From:   Saeed Mahameed <saeedm@....mellanox.co.il>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [PATCH net-next] net/mlx4_en: CHECKSUM_COMPLETE support for fragments

On Tue, Mar 27, 2018 at 2:21 PM, Eric Dumazet <edumazet@...gle.com> wrote:
> Refine the RX check summing handling to propagate the
> hardware provided checksum so that we do not have to
> compute it later in software.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Cc: Tariq Toukan <tariqt@...lanox.com>
> ---
>  drivers/net/ethernet/mellanox/mlx4/en_rx.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> index 05787efef492b1c0c6ce540ef73647fad91ce282..5c613c6663da51a4ae792eeb4d8956b54655786b 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> @@ -821,14 +821,12 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
>                 skb_record_rx_queue(skb, cq_ring);
>
>                 if (likely(dev->features & NETIF_F_RXCSUM)) {
> -                       if (cqe->status & cpu_to_be16(MLX4_CQE_STATUS_TCP |
> -                                                     MLX4_CQE_STATUS_UDP)) {
> +                       if ((cqe->status & cpu_to_be16(MLX4_CQE_STATUS_TCP |
> +                                                      MLX4_CQE_STATUS_UDP)) &&
> +                           (cqe->status & cpu_to_be16(MLX4_CQE_STATUS_IPOK)) &&
> +                           cqe->checksum == cpu_to_be16(0xffff)) {
>                                 bool l2_tunnel;
>

LGTM, this code even aligns better with the mlx4 HW documentation:

"When L4_CSUM field is not supported, L4 checksum for TCP/UDP packets
can be validated by: (IP_OK && (TCP || UDP)) && (checksum ==
0xFFFF))."

in the code we don't even consider L4_CSUM at the moment, As a future
patch, it could be a nice acceleration for the above 3 steps
condition.

Small comment, if we expect that  cqe->checksum is NOT likely to be
0xffff for UDP/TCP packets, maybe it is better performance wise to
move (cqe->checksum == cpu_to_be16(0xffff)) to be evaluated first in
the condition.

> -                               if (!((cqe->status & cpu_to_be16(MLX4_CQE_STATUS_IPOK)) &&
> -                                     cqe->checksum == cpu_to_be16(0xffff)))
> -                                       goto csum_none;
> -
>                                 l2_tunnel = (dev->hw_enc_features & NETIF_F_RXCSUM) &&
>                                         (cqe->vlan_my_qpn & cpu_to_be32(MLX4_CQE_L2_TUNNEL));
>                                 ip_summed = CHECKSUM_UNNECESSARY;
> --
> 2.17.0.rc1.321.gba9d0f2565-goog
>