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

[Wei Fang]

>
> 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.
>
Okay, I'll do a comparison test.

> 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.)
>
Could you explain why you expect XDP_TX should be faster than XDP_REDIRECT?
What's the problem if XDP_TX is as fast ad XDP_REDIRECT?

> > Signed-off-by: Wei Fang <wei.fang@xxxxxxx>
> > ---
> > 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.k/
> ernel.org%2Fr%2F20230725074148.2936402-1-wei.fang%40nxp.com&data=
> 05%7C01%7Cwei.fang%40nxp.com%7C9a2fc5bab84947e4bea608db933aa5
> e9%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C638265652320
> 018962%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV
> 2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=wc
> xe8nBeLS9uQrbphuNI18owgDNHJq9478V53KybWB8%3D&reserved=0
> > ---
> >   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++;
> >     }