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

Jesper Dangaard Brouer
2023-08-02T12:35:21Z

On 02/08/2023 11.59, Wei Fang wrote:
>>
>> 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.

Thanks.

>
>> 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?

First of all: I explained the changes needed to improve XDP_TX, below as
comments on the code. Please read and address.

XDP_TX should always be faster than XDP_REDIRECT, because it happens
locally in the driver and doesn't have to go through any generic
xdp_do_redirect code.

Like benchmarks shown in our XDP-paper[1] on mlx5 the graph[2] shows
XDP_TX vs XDP_REDIRECT vs. DPDK.

[1] https://dl.acm.org/doi/10.1145/3281411.3281443
[2]
https://github.com/xdp-project/xdp-paper/blob/master/figures/redirect-test.pdf

> What's the problem if XDP_TX is as fast ad 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.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++;
>>> }
>