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

[Wei Fang]

> >  		} else {
> > -			xdp_return_frame(xdpf);
> > +			xdp_return_frame_rx_napi(xdpf);
> 
> If you implement Jesper's syncing suggestions, I think you can use
> 
> 	page_pool_put_page(pool, page, 0, true);
> 
> for XDP_TX here to avoid the DMA sync on page recycle.

I tried Jasper's syncing suggestion and used page_pool_put_page() to recycle
pages, but the results does not seem to improve the performance of XDP_TX,
it even degrades the speed. 

The result of the current modification.
root@imx8mpevk:~# ./xdp2 eth0
proto 17:     260180 pkt/s
proto 17:     260373 pkt/s
proto 17:     260363 pkt/s
proto 17:     259036 pkt/s
proto 17:     260180 pkt/s
proto 17:     260048 pkt/s
proto 17:     260029 pkt/s
proto 17:     260133 pkt/s
proto 17:     260021 pkt/s
proto 17:     260203 pkt/s
proto 17:     260293 pkt/s
proto 17:     259418 pkt/s

After using the sync suggestion, the result shows as follow.
root@imx8mpevk:~# ./xdp2 eth0
proto 17:     255956 pkt/s
proto 17:     255841 pkt/s
proto 17:     255835 pkt/s
proto 17:     255381 pkt/s
proto 17:     255736 pkt/s
proto 17:     255779 pkt/s
proto 17:     254135 pkt/s
proto 17:     255584 pkt/s
proto 17:     255855 pkt/s
proto 17:     255664 pkt/s

Below are my changes, I don't know what cause it. Based on the results,
it's better to keep the current modification.

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index d5fda24a4c52..415c0cb83f84 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -77,7 +77,8 @@
 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);
+                               struct xdp_buff *xdp,
+                               u32 dma_sync_len);

 #define DRIVER_NAME    "fec"

@@ -1487,7 +1488,14 @@ 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_rx_napi(xdpf);
+                       if (txq->tx_buf[index].type == FEC_TXBUF_T_XDP_NDO)
+                               xdp_return_frame_rx_napi(xdpf);
+                       else {
+                               struct page *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 */
@@ -1557,7 +1565,8 @@ fec_enet_run_xdp(struct fec_enet_private *fep, struct bpf_prog *prog,
        act = bpf_prog_run_xdp(prog, xdp);

        /* Due xdp_adjust_tail: DMA sync for_device cover max len CPU touch */
-       sync = xdp->data_end - xdp->data_hard_start - FEC_ENET_XDP_HEADROOM;
+       sync = xdp->data_end - xdp->data;
        sync = max(sync, len);

        switch (act) {
@@ -1579,7 +1588,7 @@ fec_enet_run_xdp(struct fec_enet_private *fep, struct bpf_prog *prog,
                break;

        case XDP_TX:
-               err = fec_enet_xdp_tx_xmit(fep->netdev, xdp);
+               err = fec_enet_xdp_tx_xmit(fep->netdev, xdp, sync);
                if (unlikely(err)) {
                        ret = FEC_ENET_XDP_CONSUMED;
                        page = virt_to_head_page(xdp->data);
@@ -3807,6 +3816,7 @@ 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)
 {
        unsigned int index, status, estatus;
@@ -3840,7 +3850,7 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
                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);
+                                          dma_sync_len, DMA_BIDIRECTIONAL);
                txq->tx_buf[index].type = FEC_TXBUF_T_XDP_TX;
        }

@@ -3889,7 +3899,8 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
 }

 static int fec_enet_xdp_tx_xmit(struct net_device *ndev,
-                               struct xdp_buff *xdp)
+                               struct xdp_buff *xdp,
+                               u32 dma_sync_len)
 {
        struct xdp_frame *xdpf = xdp_convert_buff_to_frame(xdp);
        struct fec_enet_private *fep = netdev_priv(ndev);
@@ -3909,7 +3920,7 @@ static int fec_enet_xdp_tx_xmit(struct net_device *ndev,

        /* 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);
+       ret = fec_enet_txq_xmit_frame(fep, txq, xdpf, dma_sync_len, false);

        __netif_tx_unlock(nq);

@@ -3938,7 +3949,7 @@ 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], true) < 0)
+               if (fec_enet_txq_xmit_frame(fep, txq, frames[i], 0, true) < 0)
                        break;
                sent_frames++;
        }