netdev - Re: [RFC net-next v5 2/2] bnxt: Use generic HBH removal helper in tx path

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Date:   Thu, 8 Dec 2022 11:54:17 -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
Subject: Re: [RFC net-next v5 2/2] bnxt: Use generic HBH removal helper in tx path

On Wed, Dec 7, 2022 at 2:54 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>

If you have made changes since the last version, please drop these
tags.  Reviewers will provide new tags after reviewing the new
version.

> 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..6ba1cd342a80 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;
> @@ -11315,6 +11318,7 @@ static bool bnxt_exthdr_check(struct bnxt *bp, struct sk_buff *skb, int nw_off,
>                               u8 **nextp)
>  {
>         struct ipv6hdr *ip6h = (struct ipv6hdr *)(skb->data + nw_off);
> +       struct hop_jumbo_hdr *jhdr;
>         int hdr_count = 0;
>         u8 *nexthdr;
>         int start;
> @@ -11342,9 +11346,27 @@ 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;
> +
> +                       jhdr = (struct hop_jumbo_hdr *)nexthdr;

I already explained when reviewing your last version that nexthdr
initially points to the next header field within the ipv6 header so
this won't work.  If you cast it to jhdr, jhdr will be at offset 6 of
the ipv6 header.  It won't be pointing to the extension header.  You
need to do:

jhdr = (struct hop_jumbo_hdr *)hp

hp is pointing to the extension header.

Thanks.

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

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