Subject: Re: [PATCH v3 bpf-next] bpf: devmap: move drop error path to devmap for XDP_REDIRECT

From: Jesper Dangaard Brouer <[email-masked]>
Date: Mon, 8 Mar 2021 15:02:11 +0100

On Mon,  8 Mar 2021 12:06:58 +0100
Lorenzo Bianconi <[email-masked]> wrote:

> We want to change the current ndo_xdp_xmit drop semantics because
> it will allow us to implement better queue overflow handling.
> This is working towards the larger goal of a XDP TX queue-hook.
> Move XDP_REDIRECT error path handling from each XDP ethernet driver to
> devmap code. According to the new APIs, the driver running the
> ndo_xdp_xmit pointer, will break tx loop whenever the hw reports a tx
> error and it will just return to devmap caller the number of successfully
> transmitted frames. It will be devmap responsability to free dropped
> frames.
> Move each XDP ndo_xdp_xmit capable driver to the new APIs:
> - veth
> - virtio-net
> - mvneta
> - mvpp2
> - socionext
> - amazon ena
> - bnxt
> - freescale (dpaa2, dpaa)
> - xen-frontend
> - qede
> - ice
> - igb
> - ixgbe
> - i40e
> - mlx5
> - ti (cpsw, cpsw-new)
> - tun
> - sfc
> 
> Acked-by: Edward Cree <[email-masked]>
> Reviewed-by: Ioana Ciornei <[email-masked]>
> Reviewed-by: Ilias Apalodimas <[email-masked]>
> Signed-off-by: Lorenzo Bianconi <[email-masked]>
> ---
> More details about the new ndo_xdp_xmit design can be found here [0].
> 
> [0] https://github.com/xdp-project/xdp-project/blob/master/areas/core/redesign01_ndo_xdp_xmit.org
> 
> Changes since v2:
> - drop wrong comment in ena driver
> - simplify drop condition using unlikey in the for condition of devmap code
> - rebase on top of bpf-next
> - collect acked-by/reviewed-by
> 
> Changes since v1:
> - rebase on top of bpf-next
> - add driver maintainers in cc
> - add Edward's ack
> ---
>  drivers/net/ethernet/amazon/ena/ena_netdev.c  | 21 ++++++-------
>  drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c | 20 +++++--------
>  .../net/ethernet/freescale/dpaa/dpaa_eth.c    | 12 ++++----
>  .../net/ethernet/freescale/dpaa2/dpaa2-eth.c  |  2 --
>  drivers/net/ethernet/intel/i40e/i40e_txrx.c   | 15 +++++-----
>  drivers/net/ethernet/intel/ice/ice_txrx.c     | 15 +++++-----
>  drivers/net/ethernet/intel/igb/igb_main.c     | 11 ++++---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 11 ++++---
>  drivers/net/ethernet/marvell/mvneta.c         | 13 ++++----
>  .../net/ethernet/marvell/mvpp2/mvpp2_main.c   | 13 ++++----
>  .../net/ethernet/mellanox/mlx5/core/en/xdp.c  | 15 ++++------
>  drivers/net/ethernet/qlogic/qede/qede_fp.c    | 19 +++++-------
>  drivers/net/ethernet/sfc/tx.c                 | 15 +---------
>  drivers/net/ethernet/socionext/netsec.c       | 16 +++++-----
>  drivers/net/ethernet/ti/cpsw.c                | 14 ++++-----
>  drivers/net/ethernet/ti/cpsw_new.c            | 14 ++++-----
>  drivers/net/ethernet/ti/cpsw_priv.c           | 11 +++----
>  drivers/net/tun.c                             | 15 ++++++----
>  drivers/net/veth.c                            | 28 +++++++++--------
>  drivers/net/virtio_net.c                      | 25 ++++++++--------
>  drivers/net/xen-netfront.c                    | 18 +++++------
>  kernel/bpf/devmap.c                           | 30 ++++++++-----------
>  22 files changed, 153 insertions(+), 200 deletions(-)

Acked-by: Jesper Dangaard Brouer <[email-masked]>

Acking core changes to bpf/devmap.c (kept below).
I've only skimmed the driver changes.

> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index 85d9d1b72a33..d6330bbe1209 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -330,7 +330,7 @@ bool dev_map_can_have_prog(struct bpf_map *map)
>  static void bq_xmit_all(struct xdp_dev_bulk_queue *bq, u32 flags)
>  {
>  	struct net_device *dev = bq->dev;
> -	int sent = 0, drops = 0, err = 0;
> +	int sent = 0, err = 0;
>  	int i;
>  
>  	if (unlikely(!bq->count))
> @@ -344,29 +344,23 @@ static void bq_xmit_all(struct xdp_dev_bulk_queue *bq, u32 flags)
>  
>  	sent = dev->netdev_ops->ndo_xdp_xmit(dev, bq->count, bq->q, flags);
>  	if (sent < 0) {
> +		/* If ndo_xdp_xmit fails with an errno, no frames have
> +		 * been xmit'ed.
> +		 */
>  		err = sent;
>  		sent = 0;
> -		goto error;
>  	}
> -	drops = bq->count - sent;
> -out:
> -	bq->count = 0;
>  
> -	trace_xdp_devmap_xmit(bq->dev_rx, dev, sent, drops, err);
> -	bq->dev_rx = NULL;
> -	__list_del_clearprev(&bq->flush_node);
> -	return;
> -error:
> -	/* If ndo_xdp_xmit fails with an errno, no frames have been
> -	 * xmit'ed and it's our responsibility to them free all.
> +	/* If not all frames have been transmitted, it is our
> +	 * responsibility to free them
>  	 */
> -	for (i = 0; i < bq->count; i++) {
> -		struct xdp_frame *xdpf = bq->q[i];
> +	for (i = sent; unlikely(i < bq->count); i++)
> +		xdp_return_frame_rx_napi(bq->q[i]);
>  
> -		xdp_return_frame_rx_napi(xdpf);
> -		drops++;
> -	}
> -	goto out;
> +	trace_xdp_devmap_xmit(bq->dev_rx, dev, sent, bq->count - sent, err);
> +	bq->dev_rx = NULL;
> +	bq->count = 0;
> +	__list_del_clearprev(&bq->flush_node);
>  }
>  
>  /* __dev_flush is called from xdp_do_flush() which _must_ be signaled

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer