Subject: Re: [PATCH net-next] net: lan966x: Don't use xdp_frame when action is XDP_TX

From: Maciej Fijalkowski <[email-masked]>
Date: Thu, 20 Apr 2023 22:52:45 +0200

On Thu, Apr 20, 2023 at 02:11:52PM +0200, Horatiu Vultur wrote:

'net: ' in patch subject is excessive to me

> When the action of an xdp program was XDP_TX, lan966x was creating
> a xdp_frame and use this one to send the frame back. But it is also
> possible to send back the frame without needing a xdp_frame, because
> it possible to send it back using the page.

s/it/it is

> And then once the frame is transmitted is possible to use directly
> page_pool_recycle_direct as lan966x is using page pools.
> This would save some CPU usage on this path.

i remember this optimization gave me noticeable perf improvement, would
you mind sharing it in % on your side?

> 
> Signed-off-by: Horatiu Vultur <[email-masked]>
> ---
>  .../ethernet/microchip/lan966x/lan966x_fdma.c | 35 +++++++++++--------
>  .../ethernet/microchip/lan966x/lan966x_main.h |  2 ++
>  .../ethernet/microchip/lan966x/lan966x_xdp.c  | 11 +++---
>  3 files changed, 27 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> index 2ed76bb61a731..7947259e67e4e 100644
> --- a/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_fdma.c
> @@ -390,6 +390,7 @@ static void lan966x_fdma_stop_netdev(struct lan966x *lan966x)
>  static void lan966x_fdma_tx_clear_buf(struct lan966x *lan966x, int weight)
>  {
>  	struct lan966x_tx *tx = &lan966x->tx;
> +	struct lan966x_rx *rx = &lan966x->rx;
>  	struct lan966x_tx_dcb_buf *dcb_buf;
>  	struct xdp_frame_bulk bq;
>  	struct lan966x_db *db;
> @@ -432,7 +433,8 @@ static void lan966x_fdma_tx_clear_buf(struct lan966x *lan966x, int weight)
>  			if (dcb_buf->xdp_ndo)
>  				xdp_return_frame_bulk(dcb_buf->data.xdpf, &bq);
>  			else
> -				xdp_return_frame_rx_napi(dcb_buf->data.xdpf);
> +				page_pool_recycle_direct(rx->page_pool,
> +							 dcb_buf->data.page);
>  		}
>  
>  		clear = true;
> @@ -702,6 +704,7 @@ static void lan966x_fdma_tx_start(struct lan966x_tx *tx, int next_to_use)
>  int lan966x_fdma_xmit_xdpf(struct lan966x_port *port,
>  			   struct xdp_frame *xdpf,
>  			   struct page *page,
> +			   u32 len,

agreed with Olek regarding arguments reduction here

>  			   bool dma_map)
>  {
>  	struct lan966x *lan966x = port->lan966x;
> @@ -722,6 +725,15 @@ int lan966x_fdma_xmit_xdpf(struct lan966x_port *port,
>  		goto out;
>  	}
>  
> +	/* Fill up the buffer */
> +	next_dcb_buf = &tx->dcbs_buf[next_to_use];
> +	next_dcb_buf->use_skb = false;
> +	next_dcb_buf->xdp_ndo = dma_map;

a bit misleading that xdp_ndo is a bool :P

> +	next_dcb_buf->len = len + IFH_LEN_BYTES;
> +	next_dcb_buf->used = true;
> +	next_dcb_buf->ptp = false;
> +	next_dcb_buf->dev = port->dev;
> +
>  	/* Generate new IFH */
>  	if (dma_map) {
>  		if (xdpf->headroom < IFH_LEN_BYTES) {
> @@ -736,16 +748,18 @@ int lan966x_fdma_xmit_xdpf(struct lan966x_port *port,
>  
>  		dma_addr = dma_map_single(lan966x->dev,
>  					  xdpf->data - IFH_LEN_BYTES,
> -					  xdpf->len + IFH_LEN_BYTES,
> +					  len + IFH_LEN_BYTES,
>  					  DMA_TO_DEVICE);
>  		if (dma_mapping_error(lan966x->dev, dma_addr)) {
>  			ret = NETDEV_TX_OK;
>  			goto out;
>  		}
>  
> +		next_dcb_buf->data.xdpf = xdpf;
> +
>  		/* Setup next dcb */
>  		lan966x_fdma_tx_setup_dcb(tx, next_to_use,
> -					  xdpf->len + IFH_LEN_BYTES,
> +					  len + IFH_LEN_BYTES,
>  					  dma_addr);
>  	} else {
>  		ifh = page_address(page) + XDP_PACKET_HEADROOM;
> @@ -756,25 +770,18 @@ int lan966x_fdma_xmit_xdpf(struct lan966x_port *port,
>  		dma_addr = page_pool_get_dma_addr(page);
>  		dma_sync_single_for_device(lan966x->dev,
>  					   dma_addr + XDP_PACKET_HEADROOM,
> -					   xdpf->len + IFH_LEN_BYTES,
> +					   len + IFH_LEN_BYTES,
>  					   DMA_TO_DEVICE);
>  
> +		next_dcb_buf->data.page = page;
> +
>  		/* Setup next dcb */
>  		lan966x_fdma_tx_setup_dcb(tx, next_to_use,
> -					  xdpf->len + IFH_LEN_BYTES,
> +					  len + IFH_LEN_BYTES,
>  					  dma_addr + XDP_PACKET_HEADROOM);
>  	}
>  
> -	/* Fill up the buffer */
> -	next_dcb_buf = &tx->dcbs_buf[next_to_use];
> -	next_dcb_buf->use_skb = false;
> -	next_dcb_buf->data.xdpf = xdpf;
> -	next_dcb_buf->xdp_ndo = dma_map;
> -	next_dcb_buf->len = xdpf->len + IFH_LEN_BYTES;
>  	next_dcb_buf->dma_addr = dma_addr;
> -	next_dcb_buf->used = true;
> -	next_dcb_buf->ptp = false;
> -	next_dcb_buf->dev = port->dev;
>  
>  	/* Start the transmission */
>  	lan966x_fdma_tx_start(tx, next_to_use);
> diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_main.h b/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
> index 851afb0166b19..59da35a2c93d4 100644
> --- a/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
> +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_main.h
> @@ -243,6 +243,7 @@ struct lan966x_tx_dcb_buf {
>  	union {
>  		struct sk_buff *skb;
>  		struct xdp_frame *xdpf;
> +		struct page *page;
>  	} data;
>  	u32 len;
>  	u32 used : 1;
> @@ -544,6 +545,7 @@ int lan966x_fdma_xmit(struct sk_buff *skb, __be32 *ifh, struct net_device *dev);
>  int lan966x_fdma_xmit_xdpf(struct lan966x_port *port,
>  			   struct xdp_frame *frame,
>  			   struct page *page,
> +			   u32 len,
>  			   bool dma_map);
>  int lan966x_fdma_change_mtu(struct lan966x *lan966x);
>  void lan966x_fdma_netdev_init(struct lan966x *lan966x, struct net_device *dev);
> diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c b/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c
> index 2e6f486ec67d7..a8ad1f4e431cb 100644
> --- a/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c
> +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c
> @@ -62,7 +62,7 @@ int lan966x_xdp_xmit(struct net_device *dev,
>  		struct xdp_frame *xdpf = frames[i];
>  		int err;
>  
> -		err = lan966x_fdma_xmit_xdpf(port, xdpf, NULL, true);
> +		err = lan966x_fdma_xmit_xdpf(port, xdpf, NULL, xdpf->len, true);
>  		if (err)
>  			break;
>  
> @@ -76,7 +76,6 @@ int lan966x_xdp_run(struct lan966x_port *port, struct page *page, u32 data_len)
>  {
>  	struct bpf_prog *xdp_prog = port->xdp_prog;
>  	struct lan966x *lan966x = port->lan966x;
> -	struct xdp_frame *xdpf;
>  	struct xdp_buff xdp;
>  	u32 act;
>  
> @@ -90,11 +89,9 @@ int lan966x_xdp_run(struct lan966x_port *port, struct page *page, u32 data_len)
>  	case XDP_PASS:
>  		return FDMA_PASS;
>  	case XDP_TX:
> -		xdpf = xdp_convert_buff_to_frame(&xdp);
> -		if (!xdpf)
> -			return FDMA_DROP;
> -
> -		return lan966x_fdma_xmit_xdpf(port, xdpf, page, false) ?
> +		return lan966x_fdma_xmit_xdpf(port, NULL, page,
> +					      data_len - IFH_LEN_BYTES,
> +					      false) ?
>  		       FDMA_DROP : FDMA_TX;
>  	case XDP_REDIRECT:
>  		if (xdp_do_redirect(port->dev, &xdp, xdp_prog))
> -- 
> 2.38.0
>