netdev - Re: [RFC net-next v4 2/2] bnxt: Use generic HBH removal helper in tx path

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Date:   Mon, 5 Dec 2022 06:14:10 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Coco Li <lixiaoyan@...gle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Michael Chan <michael.chan@...adcom.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC net-next v4 2/2] bnxt: Use generic HBH removal helper in tx path

On Fri, Dec 2, 2022 at 11:12 PM Coco Li <lixiaoyan@...gle.com> wrote:
>
> Eric Dumazet implemented Big TCP that allowed bigger TSO/GRO packet sizes
> for IPv6 traffic. See patch series:
> 'commit 89527be8d8d6 ("net: add IFLA_TSO_{MAX_SIZE|SEGS} attributes")'
>
> This reduces the number of packets traversing the networking stack and
> should usually improves performance. However, it also inserts a
> temporary Hop-by-hop IPv6 extension header.
>
> Using the HBH header removal method in the previous path, the extra header
> be removed in bnxt drivers to allow it to send big TCP packets (bigger
> TSO packets) as well.
>
> Tested:
> Compiled locally
>
> To further test functional correctness, update the GSO/GRO limit on the
> physical NIC:
>
> ip link set eth0 gso_max_size 181000
> ip link set eth0 gro_max_size 181000
>
> Note that if there are bonding or ipvan devices on top of the physical
> NIC, their GSO sizes need to be updated as well.
>
> Then, IPv6/TCP packets with sizes larger than 64k can be observed.
>
> Big TCP functionality is tested by Michael, feature checks not yet.
>
> Tested by Michael:
> I've confirmed with our hardware team that this is supported by our
> chips, and I've tested it up to gso_max_size of 524280.  Thanks.
>
> Tested-by: Michael Chan <michael.chan@...adcom.com>
> Reviewed-by: Michael Chan <michael.chan@...adcom.com>
> Signed-off-by: Coco Li <lixiaoyan@...gle.com>
> ---
>  drivers/net/ethernet/broadcom/bnxt/bnxt.c | 26 ++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> index 0fe164b42c5d..c2713cb5debd 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> @@ -389,6 +389,9 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
>                         return NETDEV_TX_BUSY;
>         }
>
> +       if (unlikely(ipv6_hopopt_jumbo_remove(skb)))
> +               goto tx_free;
> +
>         length = skb->len;
>         len = skb_headlen(skb);
>         last_frag = skb_shinfo(skb)->nr_frags;
> @@ -11342,9 +11345,28 @@ static bool bnxt_exthdr_check(struct bnxt *bp, struct sk_buff *skb, int nw_off,
>
>                 if (hdrlen > 64)
>                         return false;
> +
> +               /* The ext header may be a hop-by-hop header inserted for
> +                * big TCP purposes. This will be removed before sending
> +                * from NIC, so do not count it.
> +                */
> +               if (*nexthdr == NEXTHDR_HOP) {
> +                       if (likely(skb->len <= GRO_LEGACY_MAX_SIZE))
> +                               goto increment_hdr;
> +
> +                       struct hop_jumbo_hdr *jhdr = (struct hop_jumbo_hdr *)(nexthdr + hdrlen);

We discourage adding a variable declaration in the middle of code.

> +
> +                       if (jhdr->tlv_type != IPV6_TLV_JUMBO || jhdr->hdrlen != 0 ||
> +                           (jhdr->nexthdr != IPPROTO_TCP && jhdr->nexthdr != IPPROTO_UDP))

Why testing IPPROTO_UDP ? I do not think we support BIG UDP yet.

> +                               goto increment_hdr;
> +
> +                       goto next_hdr;
> +               }
> +increment_hdr:
> +               hdr_count++;
> +next_hdr:
>                 nexthdr = &hp->nexthdr;
>                 start += hdrlen;
> -               hdr_count++;
>         }
>         if (nextp) {
>                 /* Caller will check inner protocol */
> @@ -13657,6 +13679,8 @@ static int bnxt_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
>                 dev->features &= ~NETIF_F_LRO;
>         dev->priv_flags |= IFF_UNICAST_FLT;
>
> +       netif_set_tso_max_size(dev, GSO_MAX_SIZE);
> +
>  #ifdef CONFIG_BNXT_SRIOV
>         init_waitqueue_head(&bp->sriov_cfg_wait);
>  #endif
> --
> 2.39.0.rc0.267.gcb52ba06e7-goog
>