netdev - Re: [PATCH net-next v3 2/5] net: Disable GRO_HW when generic XDP is installed on a device.

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Message-ID: <CAKgT0UcbjF+c+eoNTDrp-JQvC5k3jZpNN3H1JCge00MzYG=rhA@mail.gmail.com>
Date:   Sat, 9 Dec 2017 10:56:07 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Michael Chan <michael.chan@...adcom.com>
Cc:     David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        Andrew Gospodarek <andrew.gospodarek@...adcom.com>,
        Ariel Elior <Ariel.Elior@...ium.com>,
        everest-linux-l2@...ium.com
Subject: Re: [PATCH net-next v3 2/5] net: Disable GRO_HW when generic XDP is
 installed on a device.

On Fri, Dec 8, 2017 at 10:27 PM, Michael Chan <michael.chan@...adcom.com> wrote:
> Hardware should not aggregate any packets when generic XDP is installed.
>
> Cc: Ariel Elior <Ariel.Elior@...ium.com>
> Cc: everest-linux-l2@...ium.com
> Signed-off-by: Michael Chan <michael.chan@...adcom.com>
> ---
>  net/core/dev.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 6ebd0e7..ec08ace 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1542,6 +1542,29 @@ void dev_disable_lro(struct net_device *dev)
>  }
>  EXPORT_SYMBOL(dev_disable_lro);
>
> +/**
> + *     dev_disable_gro_hw - disable HW Generic Receive Offload on a device
> + *     @dev: device
> + *
> + *     Disable HW Generic Receive Offload (GRO_HW) on a net device.  Must be
> + *     called under RTNL.  This is needed if Generic XDP is installed on
> + *     the device.
> + */
> +static void dev_disable_gro_hw(struct net_device *dev)
> +{
> +       struct net_device *lower_dev;
> +       struct list_head *iter;
> +
> +       dev->wanted_features &= ~NETIF_F_GRO_HW;
> +       netdev_update_features(dev);
> +
> +       if (unlikely(dev->features & NETIF_F_GRO_HW))
> +               netdev_WARN(dev, "failed to disable GRO_HW!\n");
> +
> +       netdev_for_each_lower_dev(dev, lower_dev, iter)
> +               dev_disable_gro_hw(lower_dev);

I think these two lines are redundant in dev_disable_lro, since
netdev_update_features should propagate the disable to all of the
lower devices. Also this doesn't prevent the lower devices from
re-enabling gro_hw.

> +}
> +
>  static int call_netdevice_notifier(struct notifier_block *nb, unsigned long val,
>                                    struct net_device *dev)
>  {
> @@ -4564,6 +4587,7 @@ static int generic_xdp_install(struct net_device *dev, struct netdev_bpf *xdp)
>                 } else if (new && !old) {
>                         static_key_slow_inc(&generic_xdp_needed);
>                         dev_disable_lro(dev);
> +                       dev_disable_gro_hw(dev);
>                 }
>                 break;
>
> --
> 1.8.3.1
>