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Date: Thu, 10 Aug 2023 15:58:33 +0200
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Wei Fang <wei.fang@....com>, davem@...emloft.net,
edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
shenwei.wang@....com, xiaoning.wang@....com, ast@...nel.org,
daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
larysa.zaremba@...el.com, aleksander.lobakin@...el.com,
jbrouer@...hat.com, netdev@...r.kernel.org
Cc: linux-imx@....com, linux-kernel@...r.kernel.org,
bpf@...r.kernel.org
Subject: Re: [PATCH V5 net-next 1/2] net: fec: add XDP_TX feature support
On 10/08/2023 08.45, 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 in XDP_DRV mode and XDP_SKB
> mode respectively on i.MX8MP-EVK platform, and as suggested by
> Jesper, I also tested the performance of XDP_REDIRECT on the
> same platform. And the test steps and results are as follows.
>
> XDP_TX test:
> Step 1: One board is used as generator and connects to switch,and
> the FEC port of DUT also connects to the switch. Both boards with
> flow control off. Then the generator runs the
> pktgen_sample03_burst_single_flow.sh script to generate and send
> burst traffic to DUT. Note that the size of packet was set to 64
> bytes and the procotol of packet was UDP in my test scenario. In
> addtion, the SMAC of the packet need to be different from the MAC
> of the generator, because the xdp2 program will swap the DMAC and
> SMAC of the packet and send it back to the generator. If the SMAC
> of the generated packet is the MAC of the generator, the generator
> will receive the returned traffic which increase the CPU loading
> and significantly degrade the transmit speed of the generator, and
> finally it affects the test of XDP_TX performance.
>
Great that you included this description.
> Step 2: The DUT runs the xdp2 program to transmit received UDP
> packets back out on the same port where they were received.
>
> root@...8mpevk:~# ./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
>
Nice performance results! :-)
> root@...8mpevk:~# ./xdp2 -S eth0
> proto 17: 160604 pkt/s
> proto 17: 160708 pkt/s
> proto 17: 160564 pkt/s
> proto 17: 160684 pkt/s
> proto 17: 160640 pkt/s
> proto 17: 160720 pkt/s
>
> The above results show that the XDP_TX performance of XDP_DRV mode
> is much better than XDP_SKB mode, more than twice that of XDP_SKB
> mode, which is in line with our expectation.
>
> XDP_REDIRECT test:
> Step1: Both the generator and the FEC port of the DUT connet to the
> switch port. All the ports with flow control off, then the generator
> runs the pktgen script to generate and send burst traffic to DUT.
> Note that the size of packet was set to 64 bytes and the procotol of
> packet was UDP in my test scenario.
>
> Step2: The DUT runs the xdp_redirect program to redirect the traffic
> from the FEC port to the FEC port itself.
>
> root@...8mpevk:~# ./xdp_redirect eth0 eth0
> Redirecting from eth0 (ifindex 2; driver fec) to eth0
> (ifindex 2; driver fec)
> Summary 232,302 rx/s 0 err,drop/s 232,344 xmit/s
> Summary 234,579 rx/s 0 err,drop/s 234,577 xmit/s
> Summary 235,548 rx/s 0 err,drop/s 235,549 xmit/s
> Summary 234,704 rx/s 0 err,drop/s 234,703 xmit/s
> Summary 235,504 rx/s 0 err,drop/s 235,504 xmit/s
> Summary 235,223 rx/s 0 err,drop/s 235,224 xmit/s
> Summary 234,509 rx/s 0 err,drop/s 234,507 xmit/s
> Summary 235,481 rx/s 0 err,drop/s 235,482 xmit/s
> Summary 234,684 rx/s 0 err,drop/s 234,683 xmit/s
> Summary 235,520 rx/s 0 err,drop/s 235,520 xmit/s
> Summary 235,461 rx/s 0 err,drop/s 235,461 xmit/s
> Summary 234,627 rx/s 0 err,drop/s 234,627 xmit/s
> Summary 235,611 rx/s 0 err,drop/s 235,611 xmit/s
> Packets received : 3,053,753
> Average packets/s : 234,904
> Packets transmitted : 3,053,792
> Average transmit/s : 234,907
>
> Compared the performance of XDP_TX with XDP_REDIRECT, XDP_TX is also
> much better than XDP_REDIRECT. It's also in line with our expectation.
>
> Signed-off-by: Wei Fang <wei.fang@....com>
> Suggested-by: Jesper Dangaard Brouer <hawk@...nel.org>
> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> Reviewed-by: Larysa Zaremba <larysa.zaremba@...el.com>
> ---
If you add below code comment you can add my ACK in V6:
Acked-by: Jesper Dangaard Brouer <hawk@...nel.org>
> 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
>
> V4 changes:
> 1. Based on Jakub's comments, add trace_xdp_exception() for the
> error path of XDP_TX.
>
> V5: changes:
> 1. Implement Jesper's "sync_dma_len" suggestion and simultaneously
> use page_pool_put_page(pool, page, 0, true) for XDP_TX to avoid
> the DMA sync on page recycle, which is suggested by Jakub.
> 2. Based on Jesper's suggestion, add a benchmark comparison between
> XDP_TX and XDP_REDIRECT. So the commit message is also modified
> synchronously.
> ---
> drivers/net/ethernet/freescale/fec.h | 1 +
> drivers/net/ethernet/freescale/fec_main.c | 104 +++++++++++++++++-----
> 2 files changed, 84 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/net/ethernet/freescale/fec.h b/drivers/net/ethernet/freescale/fec.h
> index 5ca9906d7c6a..7bb02a9da2a6 100644
> --- a/drivers/net/ethernet/freescale/fec.h
> +++ b/drivers/net/ethernet/freescale/fec.h
> @@ -548,6 +548,7 @@ 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 43f14cec91e9..30b01985be7c 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -68,6 +68,7 @@
> #include <soc/imx/cpuidle.h>
> #include <linux/filter.h>
> #include <linux/bpf.h>
> +#include <linux/bpf_trace.h>
>
> #include <asm/cacheflush.h>
>
> @@ -75,6 +76,9 @@
>
> 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 fec_enet_private *fep,
> + int cpu, struct xdp_buff *xdp,
> + u32 dma_sync_len);
>
> #define DRIVER_NAME "fec"
>
> @@ -960,7 +964,8 @@ 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),
> @@ -1423,13 +1428,14 @@ 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),
> DMA_TO_DEVICE);
> bdp->cbd_bufaddr = cpu_to_fec32(0);
> - if (!xdpf) {
> + if (unlikely(!xdpf)) {
> txq->tx_buf[index].type = FEC_TXBUF_T_SKB;
> goto tx_buf_done;
> }
> @@ -1482,7 +1488,13 @@ 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);
> + 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);
> +
I think this usage of page_pool_put_page() with dma_sync_size=0 requires
a comment, else we will forget why this okay...
I suggest:
/* PP dma_sync_size=0 as xmit already synced DMA for_device */
> + page_pool_put_page(page->pp, page, 0, true);
> + }
>
> txq->tx_buf[index].xdp = NULL;
> /* restore default tx buffer type: FEC_TXBUF_T_SKB */
> @@ -1541,7 +1553,7 @@ static void fec_enet_update_cbd(struct fec_enet_priv_rx_q *rxq,
>
> static u32
> fec_enet_run_xdp(struct fec_enet_private *fep, struct bpf_prog *prog,
> - struct xdp_buff *xdp, struct fec_enet_priv_rx_q *rxq, int index)
> + struct xdp_buff *xdp, struct fec_enet_priv_rx_q *rxq, int cpu)
> {
> unsigned int sync, len = xdp->data_end - xdp->data;
> u32 ret = FEC_ENET_XDP_PASS;
> @@ -1551,8 +1563,10 @@ 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;
> + /* Due xdp_adjust_tail and xdp_adjust_head: DMA sync for_device cover
> + * max len CPU touch
> + */
> + sync = xdp->data_end - xdp->data;
> sync = max(sync, len);
>
> switch (act) {
> @@ -1573,11 +1587,19 @@ 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, cpu, xdp, sync);
> + if (unlikely(err)) {
> + ret = FEC_ENET_XDP_CONSUMED;
> + page = virt_to_head_page(xdp->data);
> + page_pool_put_page(rxq->page_pool, page, sync, true);
> + trace_xdp_exception(fep->netdev, prog, act);
> + } else {
> + ret = FEC_ENET_XDP_TX;
> + }
> + break;
> +
> + default:
> bpf_warn_invalid_xdp_action(fep->netdev, prog, act);
> fallthrough;
>
> @@ -1619,6 +1641,7 @@ fec_enet_rx_queue(struct net_device *ndev, int budget, u16 queue_id)
> struct bpf_prog *xdp_prog = READ_ONCE(fep->xdp_prog);
> u32 ret, xdp_result = FEC_ENET_XDP_PASS;
> u32 data_start = FEC_ENET_XDP_HEADROOM;
> + int cpu = smp_processor_id();
> struct xdp_buff xdp;
> struct page *page;
> u32 sub_len = 4;
> @@ -1697,7 +1720,7 @@ fec_enet_rx_queue(struct net_device *ndev, int budget, u16 queue_id)
> /* subtract 16bit shift and FCS */
> xdp_prepare_buff(&xdp, page_address(page),
> data_start, pkt_len - sub_len, false);
> - ret = fec_enet_run_xdp(fep, xdp_prog, &xdp, rxq, index);
> + ret = fec_enet_run_xdp(fep, xdp_prog, &xdp, rxq, cpu);
> xdp_result |= ret;
> if (ret != FEC_ENET_XDP_PASS)
> goto rx_processing_done;
> @@ -3766,7 +3789,8 @@ 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,
> + u32 dma_sync_len, bool ndo_xmit)
> {
> unsigned int index, status, estatus;
> struct bufdesc *bdp;
> @@ -3786,10 +3810,24 @@ 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,
> + dma_sync_len, DMA_BIDIRECTIONAL);
DMA sync for_device is here, that allows recycling PP with dma_sync_size=0.
> + 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)
> @@ -3808,9 +3846,6 @@ 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.
> */
> @@ -3836,6 +3871,33 @@ static int fec_enet_txq_xmit_frame(struct fec_enet_private *fep,
> return 0;
> }
>
> +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);
> +
> + __netif_tx_lock(nq, cpu);
> +
> + /* 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);
> +
> + __netif_tx_unlock(nq);
> +
> + return ret;
> +}
> +
> static int fec_enet_xdp_xmit(struct net_device *dev,
> int num_frames,
> struct xdp_frame **frames,
> @@ -3858,7 +3920,7 @@ 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], 0, true) < 0)
> break;
> sent_frames++;
> }
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