netdev - Re: [PATCH v2 bpf-next 3/3] veth: allow jumbo frames in xdp mode

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Date:   Tue, 22 Feb 2022 18:21:56 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net, brouer@...hat.com, toke@...hat.com,
        echaudro@...hat.com, lorenzo.bianconi@...hat.com,
        toshiaki.makita1@...il.com, andrii@...nel.org
Subject: Re: [PATCH v2 bpf-next 3/3] veth: allow jumbo frames in xdp mode

On Tue, 2022-02-15 at 14:08 +0100, Lorenzo Bianconi wrote:
> Allow increasing the MTU over page boundaries on veth devices
> if the attached xdp program declares to support xdp fragments.
> Enable NETIF_F_ALL_TSO when the device is running in xdp mode.
> 
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  drivers/net/veth.c | 26 +++++++++++---------------
>  1 file changed, 11 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> index a45aaaecc21f..2e048f957bc6 100644
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -292,8 +292,6 @@ static int veth_forward_skb(struct net_device *dev, struct sk_buff *skb,
>  /* return true if the specified skb has chances of GRO aggregation
>   * Don't strive for accuracy, but try to avoid GRO overhead in the most
>   * common scenarios.
> - * When XDP is enabled, all traffic is considered eligible, as the xmit
> - * device has TSO off.
>   * When TSO is enabled on the xmit device, we are likely interested only
>   * in UDP aggregation, explicitly check for that if the skb is suspected
>   * - the sock_wfree destructor is used by UDP, ICMP and XDP sockets -
> @@ -334,7 +332,8 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
>  		 * Don't bother with napi/GRO if the skb can't be aggregated
>  		 */
>  		use_napi = rcu_access_pointer(rq->napi) &&
> -			   veth_skb_is_eligible_for_gro(dev, rcv, skb);
> +			   (rcu_access_pointer(rq->xdp_prog) ||
> +			    veth_skb_is_eligible_for_gro(dev, rcv, skb));

Sorry for the late feedback. I think the code would be more readable if
you move the additional check inside 'veth_skb_is_eligible_for_gro' and
adjust veth_skb_is_eligible_for_gro() comment accordingly.

Thanks!

Paolo