netdev - Re: [PATCH v2 net] ixgbe: allow to increase MTU to some extent with XDP enabled

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Message-ID: <CAL+tcoAci+fwk6-JsTL7+yOiom08XSpc9Y5xbTZZ=WWRjYvnuw@mail.gmail.com>
Date:   Fri, 27 Jan 2023 22:54:11 +0800
From:   Jason Xing <kerneljasonxing@...il.com>
To:     jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, richardcochran@...il.com, ast@...nel.org,
        daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
        alexandr.lobakin@...el.com
Cc:     intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH v2 net] ixgbe: allow to increase MTU to some extent with
 XDP enabled

My bad. It's not that right. Please ignore the v2 patch. I need some
time to do more studies and tests on this part.

Thanks,
Jason

On Fri, Jan 27, 2023 at 8:20 PM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> From: Jason Xing <kernelxing@...cent.com>
>
> I encountered one case where I cannot increase the MTU size directly
> from 1500 to 2000 with XDP enabled if the server is equipped with
> IXGBE card, which happened on thousands of servers in production
> environment.
>
> This patch follows the behavior of changing MTU as i40e/ice does.
>
> Referrences:
> commit 23b44513c3e6f ("ice: allow 3k MTU for XDP")
> commit 0c8493d90b6bb ("i40e: add XDP support for pass and drop actions")
>
> Link: https://lore.kernel.org/lkml/20230121085521.9566-1-kerneljasonxing@gmail.com/
> Signed-off-by: Jason Xing <kernelxing@...cent.com>
> ---
> v2:
> 1) change the commit message.
> 2) modify the logic when changing MTU size suggested by Maciej and Alexander.
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 25 ++++++++++++-------
>  1 file changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index ab8370c413f3..2c1b6eb60436 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -6777,6 +6777,18 @@ static void ixgbe_free_all_rx_resources(struct ixgbe_adapter *adapter)
>                         ixgbe_free_rx_resources(adapter->rx_ring[i]);
>  }
>
> +/**
> + * ixgbe_max_xdp_frame_size - returns the maximum allowed frame size for XDP
> + * @adapter - device handle, pointer to adapter
> + */
> +static int ixgbe_max_xdp_frame_size(struct ixgbe_adapter *adapter)
> +{
> +       if (PAGE_SIZE >= 8192 || adapter->flags2 & IXGBE_FLAG2_RX_LEGACY)
> +               return IXGBE_RXBUFFER_2K;
> +       else
> +               return IXGBE_RXBUFFER_3K;
> +}
> +
>  /**
>   * ixgbe_change_mtu - Change the Maximum Transfer Unit
>   * @netdev: network interface device structure
> @@ -6788,18 +6800,13 @@ static int ixgbe_change_mtu(struct net_device *netdev, int new_mtu)
>  {
>         struct ixgbe_adapter *adapter = netdev_priv(netdev);
>
> -       if (adapter->xdp_prog) {
> +       if (ixgbe_enabled_xdp_adapter(adapter)) {
>                 int new_frame_size = new_mtu + ETH_HLEN + ETH_FCS_LEN +
>                                      VLAN_HLEN;
> -               int i;
> -
> -               for (i = 0; i < adapter->num_rx_queues; i++) {
> -                       struct ixgbe_ring *ring = adapter->rx_ring[i];
>
> -                       if (new_frame_size > ixgbe_rx_bufsz(ring)) {
> -                               e_warn(probe, "Requested MTU size is not supported with XDP\n");
> -                               return -EINVAL;
> -                       }
> +               if (new_frame_size > ixgbe_max_xdp_frame_size(adapter)) {
> +                       e_warn(probe, "Requested MTU size is not supported with XDP\n");
> +                       return -EINVAL;
>                 }
>         }
>
> --
> 2.37.3
>