netdev - Re: [RFC net-next v2 2/2] bnxt: Use generic HBH removal helper in tx path

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Date:   Wed, 23 Nov 2022 11:42:07 -0800
From:   Michael Chan <michael.chan@...adcom.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>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Andrew Gospodarek <gospo@...adcom.com>
Subject: Re: [RFC net-next v2 2/2] bnxt: Use generic HBH removal helper in tx path

On Wed, Nov 23, 2022 at 11:16 AM 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.
>
> Signed-off-by: Coco Li <lixiaoyan@...gle.com>
> ---
>  drivers/net/ethernet/broadcom/bnxt/bnxt.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> index 0fe164b42c5d..2bfa5e9fb179 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;
> @@ -13657,6 +13660,7 @@ 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);

Our chips can only transmit TSO packets up to 64K bytes, so I think
this won't work.

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