Re: [PATCH V3 net-next] net: fec: add XDP_TX feature support

[Jesper Dangaard Brouer <jbrouer@redhat.com>]

On 31/07/2023 08.00, Wei Fang wrote:
> The XDP_TX feature is not supported before, and all the frames
> which are deemed to do XDP_TX action actually do the XDP_DROP
> action. So this patch adds the XDP_TX support to FEC driver.
> 
> I tested the performance of XDP_TX feature in XDP_DRV and XDP_SKB
> modes on i.MX8MM-EVK and i.MX8MP-EVK platforms respectively, and
> the test steps and results are as follows.
> 
> Step 1: Board A connects to the FEC port of the DUT and runs the
> pktgen_sample03_burst_single_flow.sh script to generate and send
> burst traffic to DUT. Note that the length of packet was set to
> 64 bytes and the procotol of packet was UDP in my test scenario.
> 
> Step 2: The DUT runs the xdp2 program to transmit received UDP
> packets back out on the same port where they were received.
> 

Below test result runs should have some more explaination, please.
(more inline code comments below)

> root@imx8mmevk:~# ./xdp2 eth0
> proto 17:     150326 pkt/s
> proto 17:     141920 pkt/s
> proto 17:     147338 pkt/s
> proto 17:     140783 pkt/s
> proto 17:     150400 pkt/s
> proto 17:     134651 pkt/s
> proto 17:     134676 pkt/s
> proto 17:     134959 pkt/s
> proto 17:     148152 pkt/s
> proto 17:     149885 pkt/s
> 
> root@imx8mmevk:~# ./xdp2 -S eth0
> proto 17:     131094 pkt/s
> proto 17:     134691 pkt/s
> proto 17:     138930 pkt/s
> proto 17:     129347 pkt/s
> proto 17:     133050 pkt/s
> proto 17:     132932 pkt/s
> proto 17:     136628 pkt/s
> proto 17:     132964 pkt/s
> proto 17:     131265 pkt/s
> proto 17:     135794 pkt/s
> 
> root@imx8mpevk:~# ./xdp2 eth0
> proto 17:     135817 pkt/s
> proto 17:     142776 pkt/s
> proto 17:     142237 pkt/s
> proto 17:     135673 pkt/s
> proto 17:     139508 pkt/s
> proto 17:     147340 pkt/s
> proto 17:     133329 pkt/s
> proto 17:     141171 pkt/s
> proto 17:     146917 pkt/s
> proto 17:     135488 pkt/s
> 
> root@imx8mpevk:~# ./xdp2 -S eth0
> proto 17:     133150 pkt/s
> proto 17:     133127 pkt/s
> proto 17:     133538 pkt/s
> proto 17:     133094 pkt/s
> proto 17:     133690 pkt/s
> proto 17:     133199 pkt/s
> proto 17:     133905 pkt/s
> proto 17:     132908 pkt/s
> proto 17:     133292 pkt/s
> proto 17:     133511 pkt/s
> 

For this driver, I would like to see a benchmark comparison between
XDP_TX and XDP_REDIRECT.

As below code does could create a situation where XDP_REDIRECT is just
as fast as XDP_TX.  (Note, that I expect XDP_TX to be faster than
XDP_REDIRECT.)

> Signed-off-by: Wei Fang <wei.fang@nxp.com>
> ---
> V2 changes:
> According to Jakub's comments, the V2 patch adds two changes.
> 1. Call txq_trans_cond_update() in fec_enet_xdp_tx_xmit() to avoid
> tx timeout as XDP shares the queues with kernel stack.
> 2. Tx processing shouldn't call any XDP (or page pool) APIs if the
> "budget" is 0.
> 
> V3 changes:
> 1. Remove the second change in V2, because this change has been
> separated into another patch and it has been submmitted to the
> upstream [1].
> [1] https://lore.kernel.org/r/20230725074148.2936402-1-wei.fang@nxp.com
> ---
>   drivers/net/ethernet/freescale/fec.h      |  1 +
>   drivers/net/ethernet/freescale/fec_main.c | 80 ++++++++++++++++++-----
>   2 files changed, 65 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec.h b/drivers/net/ethernet/freescale/fec.h
> index 8f1edcca96c4..f35445bddc7a 100644
> --- a/drivers/net/ethernet/freescale/fec.h
> +++ b/drivers/net/ethernet/freescale/fec.h
> @@ -547,6 +547,7 @@ enum {
>   enum fec_txbuf_type {
>   	FEC_TXBUF_T_SKB,
>   	FEC_TXBUF_T_XDP_NDO,
> +	FEC_TXBUF_T_XDP_TX,
>   };
>   
>   struct fec_tx_buffer {
> diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> index 14d0dc7ba3c9..2068fe95504e 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -75,6 +75,8 @@
>   
>   static void set_multicast_list(struct net_device *ndev);
>   static void fec_enet_itr_coal_set(struct net_device *ndev);
> +static int fec_enet_xdp_tx_xmit(struct net_device *ndev,
> +				struct xdp_buff *xdp);
>   
>   #define DRIVER_NAME	"fec"
>   
> @@ -960,7 +962,8 @@ static void fec_enet_bd_init(struct net_device *dev)
>   					txq->tx_buf[i].skb = NULL;
>   				}
>   			} else {
> -				if (bdp->cbd_bufaddr)
> +				if (bdp->cbd_bufaddr &&
> +				    txq->tx_buf[i].type == FEC_TXBUF_T_XDP_NDO)
>   					dma_unmap_single(&fep->pdev->dev,
>   							 fec32_to_cpu(bdp->cbd_bufaddr),
>   							 fec16_to_cpu(bdp->cbd_datlen),
> @@ -1423,7 +1426,8 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id, int budget)
>   				break;
>   
>   			xdpf = txq->tx_buf[index].xdp;
> -			if (bdp->cbd_bufaddr)
> +			if (bdp->cbd_bufaddr &&
> +			    txq->tx_buf[index].type == FEC_TXBUF_T_XDP_NDO)
>   				dma_unmap_single(&fep->pdev->dev,
>   						 fec32_to_cpu(bdp->cbd_bufaddr),
>   						 fec16_to_cpu(bdp->cbd_datlen),
> @@ -1482,7 +1486,7 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id, int budget)
>   			/* Free the sk buffer associated with this last transmit */
>   			dev_kfree_skb_any(skb);
>   		} else {
> -			xdp_return_frame(xdpf);
> +			xdp_return_frame_rx_napi(xdpf);
>   
>   			txq->tx_buf[index].xdp = NULL;
>   			/* restore default tx buffer type: FEC_TXBUF_T_SKB */
> @@ -1573,11 +1577,18 @@ fec_enet_run_xdp(struct fec_enet_private *fep, struct bpf_prog *prog,
>   		}
>   		break;
>   
> -	default:
> -		bpf_warn_invalid_xdp_action(fep->netdev, prog, act);
> -		fallthrough;
> -
>   	case XDP_TX:
> +		err = fec_enet_xdp_tx_xmit(fep->netdev, xdp);

You should pass along the "sync" length value to fec_enet_xdp_tx_xmit().
Because we know DMA comes from same device (it is already DMA mapped
to), then we can do a DMA sync "to_device" with only the sync length.

> +		if (err) {

Add an unlikely(err) or do like above case XDP_REDIRECT, where it takes
the likely case "if (!err)" first.

> +			ret = FEC_ENET_XDP_CONSUMED;
> +			page = virt_to_head_page(xdp->data);
> +			page_pool_put_page(rxq->page_pool, page, sync, true);
> +		} else {
> +			ret = FEC_ENET_XDP_TX;
> +		}
> +		break;
> +
> +	default:
>   		bpf_warn_invalid_xdp_action(fep->netdev, prog, act);
>   		fallthrough;
>   
> @@ -3793,7 +3804,8 @@ fec_enet_xdp_get_tx_queue(struct fec_enet_private *fep, int index)
>   
>   static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
>   				   struct fec_enet_priv_tx_q *txq,
> -				   struct xdp_frame *frame)
> +				   struct xdp_frame *frame,
> +				   bool ndo_xmit)

E.g add parameter dma_sync_len.

>   {
>   	unsigned int index, status, estatus;
>   	struct bufdesc *bdp;
> @@ -3813,10 +3825,24 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
>   
>   	index = fec_enet_get_bd_index(bdp, &txq->bd);
>   
> -	dma_addr = dma_map_single(&fep->pdev->dev, frame->data,
> -				  frame->len, DMA_TO_DEVICE);
> -	if (dma_mapping_error(&fep->pdev->dev, dma_addr))
> -		return -ENOMEM;
> +	if (ndo_xmit) {
> +		dma_addr = dma_map_single(&fep->pdev->dev, frame->data,
> +					  frame->len, DMA_TO_DEVICE);
> +		if (dma_mapping_error(&fep->pdev->dev, dma_addr))
> +			return -ENOMEM;
> +
> +		txq->tx_buf[index].type = FEC_TXBUF_T_XDP_NDO;
> +	} else {
> +		struct page *page = virt_to_page(frame->data);
> +
> +		dma_addr = page_pool_get_dma_addr(page) + sizeof(*frame) +
> +			   frame->headroom;
> +		dma_sync_single_for_device(&fep->pdev->dev, dma_addr,
> +					   frame->len, DMA_BIDIRECTIONAL);

Optimization: use dma_sync_len here instead of frame->len.

> +		txq->tx_buf[index].type = FEC_TXBUF_T_XDP_TX;
> +	}
> +
> +	txq->tx_buf[index].xdp = frame;
>   
>   	status |= (BD_ENET_TX_INTR | BD_ENET_TX_LAST);
>   	if (fep->bufdesc_ex)
> @@ -3835,9 +3861,6 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
>   		ebdp->cbd_esc = cpu_to_fec32(estatus);
>   	}
>   
> -	txq->tx_buf[index].type = FEC_TXBUF_T_XDP_NDO;
> -	txq->tx_buf[index].xdp = frame;
> -
>   	/* Make sure the updates to rest of the descriptor are performed before
>   	 * transferring ownership.
>   	 */
> @@ -3863,6 +3886,31 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
>   	return 0;
>   }
>   
> +static int fec_enet_xdp_tx_xmit(struct net_device *ndev,
> +				struct xdp_buff *xdp)
> +{

E.g add parameter dma_sync_len.

> +	struct xdp_frame *xdpf = xdp_convert_buff_to_frame(xdp);

XDP_TX can avoid this conversion to xdp_frame.
It would requires some refactor of fec_enet_txq_xmit_frame().

> +	struct fec_enet_private *fep = netdev_priv(ndev);
> +	struct fec_enet_priv_tx_q *txq;
> +	int cpu = smp_processor_id();
> +	struct netdev_queue *nq;
> +	int queue, ret;
> +
> +	queue = fec_enet_xdp_get_tx_queue(fep, cpu);
> +	txq = fep->tx_queue[queue];
> +	nq = netdev_get_tx_queue(fep->netdev, queue);
> +
> +	__netif_tx_lock(nq, cpu);

It is sad that XDP_TX takes a lock for each frame.

> +
> +	/* Avoid tx timeout as XDP shares the queue with kernel stack */
> +	txq_trans_cond_update(nq);
> +	ret = fec_enet_txq_xmit_frame(fep, txq, xdpf, false);

Add/pass parameter dma_sync_len to fec_enet_txq_xmit_frame().


> +
> +	__netif_tx_unlock(nq);
> +
> +	return ret;
> +}
> +
>   static int fec_enet_xdp_xmit(struct net_device *dev,
>   			     int num_frames,
>   			     struct xdp_frame **frames,
> @@ -3885,7 +3933,7 @@ static int fec_enet_xdp_xmit(struct net_device *dev,
>   	/* Avoid tx timeout as XDP shares the queue with kernel stack */
>   	txq_trans_cond_update(nq);
>   	for (i = 0; i < num_frames; i++) {
> -		if (fec_enet_txq_xmit_frame(fep, txq, frames[i]) < 0)
> +		if (fec_enet_txq_xmit_frame(fep, txq, frames[i], true) < 0)
>   			break;
>   		sent_frames++;
>   	}