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

From: Wei Fang
Date: Thu Aug 03 2023 - 07:18:49 EST

>
> On 03/08/2023 05.58, Wei Fang wrote:
> >>> } 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);
>
> To Jakub, using 0 here you are trying to bypass the DMA-sync (which is valid
> as driver knows XDP_TX have already done the sync).
> The code will still call into DMA-sync calls with zero as size, so wonder if we
> should detect size zero and skip that call?
> (I mean is this something page_pool should support.)
>
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c index
> 7ca456bfab71..778d061e4f2c 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -323,7 +323,8 @@ static void page_pool_dma_sync_for_device(struct
> page_pool *pool,
> dma_addr_t dma_addr = page_pool_get_dma_addr(page);
>
> dma_sync_size = min(dma_sync_size, pool->p.max_len);
> - dma_sync_single_range_for_device(pool->p.dev, dma_addr,
> + if (dma_sync_size)
> + dma_sync_single_range_for_device(pool->p.dev,
> dma_addr,
> pool->p.offset,
> dma_sync_size,
> pool->p.dma_dir);
>
>
>
> >>
> >> 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,
>
> The optimization will only have effect on those devices which have
> dev->dma_coherent=false else DMA function [1] (e.g.
> dma_direct_sync_single_for_device) will skip the sync calls.
>
> [1]
> https://elixir.b/
> ootlin.com%2Flinux%2Fv6.5-rc4%2Fsource%2Fkernel%2Fdma%2Fdirect.h%2
> 3L63&data=05%7C01%7Cwei.fang%40nxp.com%7Cb81436deb63d41dd41a1
> 08db93f454cb%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C63
> 8266449821982804%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM
> DAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%
> 7C&sdata=CSi%2Fzld%2FucIYo6VDb9YdO91D8HKV1tbzPq8fB5X%2Bs3s%3D&
> reserved=0
>
> (Cc. Andrew Lunn)
> Does any of the imx generations have dma-noncoherent memory?
>
> And does any of these use the fec NIC driver?
>
> > it even degrades the speed.
>
> Could be low runs simply be a variation between your test runs?
>
Maybe, I just tested once before. So I test several times again, the
results of the two methods do not seem to be much different so far,
both about 255000 pkt/s.

> The specific device (imx8mpevk) this was tested on, clearly have
> dma_coherent=true, or else we would have seen a difference.
> But the code change should not have any overhead for the
> dma_coherent=true case, the only extra overhead is the extra empty DMA
> sync call with size zero (as discussed in top).
>
The FEC of i.MX8MP-EVK has dma_coherent=false, and as I mentioned
above, I did not see an obvious difference in the performance. :(

> >
> > The result of the current modification.
> > root@imx8mpevk:~# ./xdp2 eth0
> > proto 17: 260180 pkt/s
>
> These results are *significantly* better than reported in patch-1.
> What happened?!?
>
The test environment is slightly different, in patch-1, the FEC port was
directly connected to the port of another board. But in the latest test,
the ports of the two boards were connected to a switch, so the ports of
the two boards are not directly connected.

> e.g.
> root@imx8mpevk:~# ./xdp2 eth0
> proto 17: 135817 pkt/s
> proto 17: 142776 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++;
> > }
> >