Re: [PATCH V5 net-next 2/2] net: fec: improve XDP_TX performance

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On 10/08/2023 08.45, Wei Fang wrote:
As suggested by Jesper and Alexander, we can avoid converting xdp_buff
to xdp_frame in case of XDP_TX to save a bunch of CPU cycles, so that
we can further improve the XDP_TX performance.

Before this patch on i.MX8MP-EVK board, the performance shows as follows.
root@imx8mpevk:~# ./xdp2 eth0
proto 17:     353918 pkt/s
proto 17:     352923 pkt/s
proto 17:     353900 pkt/s
proto 17:     352672 pkt/s
proto 17:     353912 pkt/s
proto 17:     354219 pkt/s

After applying this patch, the performance is improved.
root@imx8mpevk:~# ./xdp2 eth0
proto 17:     369261 pkt/s
proto 17:     369267 pkt/s
proto 17:     369206 pkt/s
proto 17:     369214 pkt/s
proto 17:     369126 pkt/s
proto 17:     369272 pkt/s


So approx 4.3% improvement.

Signed-off-by: Wei Fang <wei.fang@xxxxxxx>
Suggested-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
Suggested-by: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
---
V5 changes:
New patch. Separated from the first patch, to keep track of the changes
and improvements (suggested by Jesper).

Thanks

---
  drivers/net/ethernet/freescale/fec.h      |   5 +-
  drivers/net/ethernet/freescale/fec_main.c | 134 ++++++++++++----------
  2 files changed, 73 insertions(+), 66 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec.h b/drivers/net/ethernet/freescale/fec.h
index 7bb02a9da2a6..a8fbcada6b01 100644
--- a/drivers/net/ethernet/freescale/fec.h
+++ b/drivers/net/ethernet/freescale/fec.h
@@ -552,10 +552,7 @@ enum fec_txbuf_type {
  };
struct fec_tx_buffer {
-	union {
-		struct sk_buff *skb;
-		struct xdp_frame *xdp;
-	};
+	void *buf_p;

I want to hear Olek's (Alexander) oppinion on this void pointer circus.

The rest of the patch looks correct to me so:

Reviewed-by: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>

--Jesper

  	enum fec_txbuf_type type;
  };
diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 30b01985be7c..ae6e41ad71b8 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -399,7 +399,7 @@ static void fec_dump(struct net_device *ndev)
  			fec16_to_cpu(bdp->cbd_sc),
  			fec32_to_cpu(bdp->cbd_bufaddr),
  			fec16_to_cpu(bdp->cbd_datlen),
-			txq->tx_buf[index].skb);
+			txq->tx_buf[index].buf_p);
  		bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
  		index++;
  	} while (bdp != txq->bd.base);
@@ -656,7 +656,7 @@ static int fec_enet_txq_submit_skb(struct fec_enet_priv_tx_q *txq,
index = fec_enet_get_bd_index(last_bdp, &txq->bd);
  	/* Save skb pointer */
-	txq->tx_buf[index].skb = skb;
+	txq->tx_buf[index].buf_p = skb;
/* Make sure the updates to rest of the descriptor are performed before
  	 * transferring ownership.
@@ -862,7 +862,7 @@ static int fec_enet_txq_submit_tso(struct fec_enet_priv_tx_q *txq,
  	}
/* Save skb pointer */
-	txq->tx_buf[index].skb = skb;
+	txq->tx_buf[index].buf_p = skb;
skb_tx_timestamp(skb);
  	txq->bd.cur = bdp;
@@ -959,27 +959,27 @@ static void fec_enet_bd_init(struct net_device *dev)
  							 fec32_to_cpu(bdp->cbd_bufaddr),
  							 fec16_to_cpu(bdp->cbd_datlen),
  							 DMA_TO_DEVICE);
-				if (txq->tx_buf[i].skb) {
-					dev_kfree_skb_any(txq->tx_buf[i].skb);
-					txq->tx_buf[i].skb = NULL;
-				}
-			} else {
-				if (bdp->cbd_bufaddr &&
-				    txq->tx_buf[i].type == FEC_TXBUF_T_XDP_NDO)
+				if (txq->tx_buf[i].buf_p)
+					dev_kfree_skb_any(txq->tx_buf[i].buf_p);
+			} else if (txq->tx_buf[i].type == FEC_TXBUF_T_XDP_NDO) {
+				if (bdp->cbd_bufaddr)
  					dma_unmap_single(&fep->pdev->dev,
  							 fec32_to_cpu(bdp->cbd_bufaddr),
  							 fec16_to_cpu(bdp->cbd_datlen),
  							 DMA_TO_DEVICE);
- if (txq->tx_buf[i].xdp) {
-					xdp_return_frame(txq->tx_buf[i].xdp);
-					txq->tx_buf[i].xdp = NULL;
-				}
+				if (txq->tx_buf[i].buf_p)
+					xdp_return_frame(txq->tx_buf[i].buf_p);
+			} else {
+				struct page *page = txq->tx_buf[i].buf_p;
- /* restore default tx buffer type: FEC_TXBUF_T_SKB */
-				txq->tx_buf[i].type = FEC_TXBUF_T_SKB;
+				if (page)
+					page_pool_put_page(page->pp, page, 0, false);
  			}
+ txq->tx_buf[i].buf_p = NULL;
+			/* restore default tx buffer type: FEC_TXBUF_T_SKB */
+			txq->tx_buf[i].type = FEC_TXBUF_T_SKB;
  			bdp->cbd_bufaddr = cpu_to_fec32(0);
  			bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
  		}
@@ -1386,6 +1386,8 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id, int budget)
  	struct netdev_queue *nq;
  	int	index = 0;
  	int	entries_free;
+	struct page *page;
+	int frame_len;
fep = netdev_priv(ndev); @@ -1407,8 +1409,7 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id, int budget)
  		index = fec_enet_get_bd_index(bdp, &txq->bd);
if (txq->tx_buf[index].type == FEC_TXBUF_T_SKB) {
-			skb = txq->tx_buf[index].skb;
-			txq->tx_buf[index].skb = NULL;
+			skb = txq->tx_buf[index].buf_p;
  			if (bdp->cbd_bufaddr &&
  			    !IS_TSO_HEADER(txq, fec32_to_cpu(bdp->cbd_bufaddr)))
  				dma_unmap_single(&fep->pdev->dev,
@@ -1427,18 +1428,24 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id, int budget)
  			if (unlikely(!budget))
  				break;
- xdpf = txq->tx_buf[index].xdp;
-			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),
-						 DMA_TO_DEVICE);
+			if (txq->tx_buf[index].type == FEC_TXBUF_T_XDP_NDO) {
+				xdpf = txq->tx_buf[index].buf_p;
+				if (bdp->cbd_bufaddr)
+					dma_unmap_single(&fep->pdev->dev,
+							 fec32_to_cpu(bdp->cbd_bufaddr),
+							 fec16_to_cpu(bdp->cbd_datlen),
+							 DMA_TO_DEVICE);
+			} else {
+				page = txq->tx_buf[index].buf_p;
+			}
+
  			bdp->cbd_bufaddr = cpu_to_fec32(0);
-			if (unlikely(!xdpf)) {
+			if (unlikely(!txq->tx_buf[index].buf_p)) {
  				txq->tx_buf[index].type = FEC_TXBUF_T_SKB;
  				goto tx_buf_done;
  			}
+
+			frame_len = fec16_to_cpu(bdp->cbd_datlen);
  		}
/* Check for errors. */
@@ -1462,7 +1469,7 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id, int budget)
  			if (txq->tx_buf[index].type == FEC_TXBUF_T_SKB)
  				ndev->stats.tx_bytes += skb->len;
  			else
-				ndev->stats.tx_bytes += xdpf->len;
+				ndev->stats.tx_bytes += frame_len;
  		}
/* Deferred means some collisions occurred during transmit,
@@ -1487,20 +1494,16 @@ 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 if (txq->tx_buf[index].type == FEC_TXBUF_T_XDP_NDO) {
+			xdp_return_frame_rx_napi(xdpf);
  		} else {
-			if (txq->tx_buf[index].type == FEC_TXBUF_T_XDP_NDO) {
-				xdp_return_frame_rx_napi(xdpf);
-			} else {
-				struct page *page = virt_to_head_page(xdpf->data);
-
-				page_pool_put_page(page->pp, page, 0, true);
-			}
-
-			txq->tx_buf[index].xdp = NULL;
-			/* restore default tx buffer type: FEC_TXBUF_T_SKB */
-			txq->tx_buf[index].type = FEC_TXBUF_T_SKB;
+			page_pool_put_page(page->pp, page, 0, true);
  		}
+ txq->tx_buf[index].buf_p = NULL;
+		/* restore default tx buffer type: FEC_TXBUF_T_SKB */
+		txq->tx_buf[index].type = FEC_TXBUF_T_SKB;
+
  tx_buf_done:
  		/* Make sure the update to bdp and tx_buf are performed
  		 * before dirty_tx
@@ -3230,7 +3233,6 @@ static void fec_enet_free_buffers(struct net_device *ndev)
  {
  	struct fec_enet_private *fep = netdev_priv(ndev);
  	unsigned int i;
-	struct sk_buff *skb;
  	struct fec_enet_priv_tx_q *txq;
  	struct fec_enet_priv_rx_q *rxq;
  	unsigned int q;
@@ -3255,18 +3257,23 @@ static void fec_enet_free_buffers(struct net_device *ndev)
  			kfree(txq->tx_bounce[i]);
  			txq->tx_bounce[i] = NULL;
+ if (!txq->tx_buf[i].buf_p) {
+				txq->tx_buf[i].type = FEC_TXBUF_T_SKB;
+				continue;
+			}
+
  			if (txq->tx_buf[i].type == FEC_TXBUF_T_SKB) {
-				skb = txq->tx_buf[i].skb;
-				txq->tx_buf[i].skb = NULL;
-				dev_kfree_skb(skb);
+				dev_kfree_skb(txq->tx_buf[i].buf_p);
+			} else if (txq->tx_buf[i].type == FEC_TXBUF_T_XDP_NDO) {
+				xdp_return_frame(txq->tx_buf[i].buf_p);
  			} else {
-				if (txq->tx_buf[i].xdp) {
-					xdp_return_frame(txq->tx_buf[i].xdp);
-					txq->tx_buf[i].xdp = NULL;
-				}
+				struct page *page = txq->tx_buf[i].buf_p;
- txq->tx_buf[i].type = FEC_TXBUF_T_SKB;
+				page_pool_put_page(page->pp, page, 0, false);
  			}
+
+			txq->tx_buf[i].buf_p = NULL;
+			txq->tx_buf[i].type = FEC_TXBUF_T_SKB;
  		}
  	}
  }
@@ -3789,13 +3796,14 @@ 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,
-				   u32 dma_sync_len, bool ndo_xmit)
+				   void *frame, u32 dma_sync_len,
+				   bool ndo_xmit)
  {
  	unsigned int index, status, estatus;
  	struct bufdesc *bdp;
  	dma_addr_t dma_addr;
  	int entries_free;
+	u16 frame_len;
entries_free = fec_enet_get_free_txdesc_num(txq);
  	if (entries_free < MAX_SKB_FRAGS + 1) {
@@ -3811,30 +3819,36 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
  	index = fec_enet_get_bd_index(bdp, &txq->bd);
if (ndo_xmit) {
-		dma_addr = dma_map_single(&fep->pdev->dev, frame->data,
-					  frame->len, DMA_TO_DEVICE);
+		struct xdp_frame *xdpf = frame;
+
+		dma_addr = dma_map_single(&fep->pdev->dev, xdpf->data,
+					  xdpf->len, DMA_TO_DEVICE);
  		if (dma_mapping_error(&fep->pdev->dev, dma_addr))
  			return -ENOMEM;
+ frame_len = xdpf->len;
+		txq->tx_buf[index].buf_p = xdpf;
  		txq->tx_buf[index].type = FEC_TXBUF_T_XDP_NDO;
  	} else {
-		struct page *page = virt_to_page(frame->data);
+		struct xdp_buff *xdpb = frame;
+		struct page *page;
- dma_addr = page_pool_get_dma_addr(page) + sizeof(*frame) +
-			   frame->headroom;
+		page = virt_to_page(xdpb->data);
+		dma_addr = page_pool_get_dma_addr(page) +
+			   (xdpb->data - xdpb->data_hard_start);
  		dma_sync_single_for_device(&fep->pdev->dev, dma_addr,
  					   dma_sync_len, DMA_BIDIRECTIONAL);
+		frame_len = xdpb->data_end - xdpb->data;
+		txq->tx_buf[index].buf_p = page;
  		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)
  		estatus = BD_ENET_TX_INT;
bdp->cbd_bufaddr = cpu_to_fec32(dma_addr);
-	bdp->cbd_datlen = cpu_to_fec16(frame->len);
+	bdp->cbd_datlen = cpu_to_fec16(frame_len);
if (fep->bufdesc_ex) {
  		struct bufdesc_ex *ebdp = (struct bufdesc_ex *)bdp;
@@ -3875,14 +3889,10 @@ static int fec_enet_xdp_tx_xmit(struct fec_enet_private *fep,
  				int cpu, struct xdp_buff *xdp,
  				u32 dma_sync_len)
  {
-	struct xdp_frame *xdpf = xdp_convert_buff_to_frame(xdp);
  	struct fec_enet_priv_tx_q *txq;
  	struct netdev_queue *nq;
  	int queue, ret;
- if (unlikely(!xdpf))
-		return -EFAULT;
-
  	queue = fec_enet_xdp_get_tx_queue(fep, cpu);
  	txq = fep->tx_queue[queue];
  	nq = netdev_get_tx_queue(fep->netdev, queue);
@@ -3891,7 +3901,7 @@ static int fec_enet_xdp_tx_xmit(struct fec_enet_private *fep,
/* 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, dma_sync_len, false);
+	ret = fec_enet_txq_xmit_frame(fep, txq, xdp, dma_sync_len, false);
__netif_tx_unlock(nq);




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