Subject: Re: [PATCH intel-next v3 8/8] i40e: add support for XDP multi-buffer Rx

From: Maciej Fijalkowski <[email-masked]>
Date: Tue, 14 Feb 2023 18:01:29 +0100

On Tue, Feb 14, 2023 at 06:00:18PM +0530, Tirthendu Sarkar wrote:
> This patch adds multi-buffer support for the i40e_driver.
> 
> i40e_clean_rx_irq() is modified to collate all the buffers of a packet
> before calling the XDP program. xdp_buff is built for the first frag of
> the packet and subsequent frags are added to it. 'next_to_process' is
> incremented for all non-EOP frags while 'next_to_clean' stays at the
> first descriptor of the packet. XDP program is called only on receiving
> EOP frag.
> 
> New functions are added for adding frags to xdp_buff and for post
> processing of the buffers once the xdp prog has run. For XDP_PASS this
> results in a skb with multiple fragments.
> 
> i40e_build_skb() builds the skb around xdp buffer that already contains
> frags data. So i40e_add_rx_frag() helper function is now removed. Since
> fields before 'dataref' in skb_shared_info are cleared during
> napi_skb_build(), xdp_update_skb_shared_info() is called to set those.
> 
> For i40e_construct_skb(), all the frags data needs to be copied from
> xdp_buffer's shared_skb_info to newly constructed skb's shared_skb_info.
> 
> This also means 'skb' does not need to be preserved across i40e_napi_poll()
> calls and hence is removed from i40e_ring structure.
> 
> Previously i40e_alloc_rx_buffers() was called for every 32 cleaned
> buffers. For multi-buffers this may not be optimal as there may be more
> cleaned buffers in each i40e_clean_rx_irq() call. So this is now called
> when at least half of the ring size has been cleaned.

Please align this patch with xdp_features update

> 
> Signed-off-by: Tirthendu Sarkar <[email-masked]>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c |   4 +-
>  drivers/net/ethernet/intel/i40e/i40e_txrx.c | 314 +++++++++++++-------
>  drivers/net/ethernet/intel/i40e/i40e_txrx.h |   8 -
>  3 files changed, 209 insertions(+), 117 deletions(-)
> 

(...)

>  }
>  
> +/**
> + * i40e_add_xdp_frag: Add a frag to xdp_buff
> + * @xdp: xdp_buff pointing to the data
> + * @nr_frags: return number of buffers for the packet
> + * @rx_buffer: rx_buffer holding data of the current frag
> + * @size: size of data of current frag
> + */
> +static int i40e_add_xdp_frag(struct xdp_buff *xdp, u32 *nr_frags,
> +			     struct i40e_rx_buffer *rx_buffer, u32 size)
> +{
> +	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> +
> +	if (!xdp_buff_has_frags(xdp)) {
> +		sinfo->nr_frags = 0;
> +		sinfo->xdp_frags_size = 0;
> +		xdp_buff_set_frags_flag(xdp);
> +	} else if (unlikely(sinfo->nr_frags >= MAX_SKB_FRAGS)) {
> +		/* Overflowing packet: All frags need to be dropped */
> +		return  -ENOMEM;

nit: double space

> +	}
> +
> +	__skb_fill_page_desc_noacc(sinfo, sinfo->nr_frags++, rx_buffer->page,
> +				   rx_buffer->page_offset, size);
> +
> +	sinfo->xdp_frags_size += size;
> +
> +	if (page_is_pfmemalloc(rx_buffer->page))
> +		xdp_buff_set_frag_pfmemalloc(xdp);
> +	*nr_frags = sinfo->nr_frags;
> +
> +	return 0;
> +}
> +
> +/**
> + * i40e_consume_xdp_buff - Consume all the buffers of the packet and update ntc
> + * @rx_ring: rx descriptor ring to transact packets on
> + * @xdp: xdp_buff pointing to the data
> + * @rx_buffer: rx_buffer of eop desc
> + */
> +static void i40e_consume_xdp_buff(struct i40e_ring *rx_ring,
> +				  struct xdp_buff *xdp,
> +				  struct i40e_rx_buffer *rx_buffer)
> +{
> +	i40e_process_rx_buffs(rx_ring, I40E_XDP_CONSUMED, xdp);
> +	i40e_put_rx_buffer(rx_ring, rx_buffer);
> +	rx_ring->next_to_clean = rx_ring->next_to_process;
> +	xdp->data = NULL;
> +}
> +
>  /**
>   * i40e_clean_rx_irq - Clean completed descriptors from Rx ring - bounce buf
>   * @rx_ring: rx descriptor ring to transact packets on
> @@ -2405,9 +2495,9 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
>  {
>  	unsigned int total_rx_bytes = 0, total_rx_packets = 0;
>  	u16 cleaned_count = I40E_DESC_UNUSED(rx_ring);
> +	u16 clean_threshold = rx_ring->count / 2;
>  	unsigned int offset = rx_ring->rx_offset;
>  	struct xdp_buff *xdp = &rx_ring->xdp;
> -	struct sk_buff *skb = rx_ring->skb;
>  	unsigned int xdp_xmit = 0;
>  	struct bpf_prog *xdp_prog;
>  	bool failure = false;
> @@ -2419,11 +2509,14 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
>  		u16 ntp = rx_ring->next_to_process;
>  		struct i40e_rx_buffer *rx_buffer;
>  		union i40e_rx_desc *rx_desc;
> +		struct sk_buff *skb;
>  		unsigned int size;
> +		u32 nfrags = 0;
> +		bool neop;
>  		u64 qword;
>  
>  		/* return some buffers to hardware, one at a time is too slow */
> -		if (cleaned_count >= I40E_RX_BUFFER_WRITE) {
> +		if (cleaned_count >= clean_threshold) {
>  			failure = failure ||
>  				  i40e_alloc_rx_buffers(rx_ring, cleaned_count);
>  			cleaned_count = 0;
> @@ -2461,76 +2554,83 @@ static int i40e_clean_rx_irq(struct i40e_ring *rx_ring, int budget,
>  			break;
>  
>  		i40e_trace(clean_rx_irq, rx_ring, rx_desc, xdp);
> +		/* retrieve a buffer from the ring */
>  		rx_buffer = i40e_get_rx_buffer(rx_ring, size);
>  
> -		/* retrieve a buffer from the ring */
> -		if (!skb) {
> +		neop = i40e_is_non_eop(rx_ring, rx_desc);
> +		i40e_inc_ntp(rx_ring);
> +
> +		if (!xdp->data) {
>  			unsigned char *hard_start;
>  
>  			hard_start = page_address(rx_buffer->page) +
>  				     rx_buffer->page_offset - offset;
>  			xdp_prepare_buff(xdp, hard_start, offset, size, true);
> -			xdp_buff_clear_frags_flag(xdp);
>  #if (PAGE_SIZE > 4096)
>  			/* At larger PAGE_SIZE, frame_sz depend on len size */
>  			xdp->frame_sz = i40e_rx_frame_truesize(rx_ring, size);
>  #endif
> -			xdp_res = i40e_run_xdp(rx_ring, xdp, xdp_prog);
> +		} else if (i40e_add_xdp_frag(xdp, &nfrags, rx_buffer, size) &&
> +			   !neop) {
> +			/* Overflowing packet: Drop all frags on EOP */
> +			i40e_consume_xdp_buff(rx_ring, xdp, rx_buffer);
> +			break;
>  		}
>  
> +		if (neop)
> +			continue;
> +
> +		xdp_res = i40e_run_xdp(rx_ring, xdp, xdp_prog);
> +
>  		if (xdp_res) {
> -			if (xdp_res & (I40E_XDP_TX | I40E_XDP_REDIR)) {
> -				xdp_xmit |= xdp_res;
> +			xdp_xmit |= xdp_res & (I40E_XDP_TX | I40E_XDP_REDIR);

what was wrong with having above included in the

	} else if (xdp_res & (I40E_XDP_TX | I40E_XDP_REDIR)) {

branch?

> +
> +			if (unlikely(xdp_buff_has_frags(xdp))) {
> +				i40e_process_rx_buffs(rx_ring, xdp_res, xdp);
> +				size = xdp_get_buff_len(xdp);
> +			} else if (xdp_res & (I40E_XDP_TX | I40E_XDP_REDIR)) {
>  				i40e_rx_buffer_flip(rx_buffer, xdp->frame_sz);
>  			} else {
>  				rx_buffer->pagecnt_bias++;
>  			}
>  			total_rx_bytes += size;
> -			total_rx_packets++;
> -		} else if (skb) {
> -			i40e_add_rx_frag(rx_ring, rx_buffer, skb, size);
> -		} else if (ring_uses_build_skb(rx_ring)) {
> -			skb = i40e_build_skb(rx_ring, rx_buffer, xdp);
>  		} else {
> -			skb = i40e_construct_skb(rx_ring, rx_buffer, xdp);
> -		}
> +			if (ring_uses_build_skb(rx_ring))
> +				skb = i40e_build_skb(rx_ring, xdp, nfrags);
> +			else
> +				skb = i40e_construct_skb(rx_ring, xdp, nfrags);
> +
> +			/* drop if we failed to retrieve a buffer */
> +			if (!skb) {
> +				rx_ring->rx_stats.alloc_buff_failed++;
> +				i40e_consume_xdp_buff(rx_ring, xdp, rx_buffer);
> +				break;
> +			}
>  
> -		/* exit if we failed to retrieve a buffer */
> -		if (!xdp_res && !skb) {
> -			rx_ring->rx_stats.alloc_buff_failed++;
> -			rx_buffer->pagecnt_bias++;
> -			break;
> -		}
> +			if (i40e_cleanup_headers(rx_ring, skb, rx_desc))
> +				goto process_next;
>  
> -		i40e_put_rx_buffer(rx_ring, rx_buffer);
> -		cleaned_count++;
> +			/* probably a little skewed due to removing CRC */
> +			total_rx_bytes += skb->len;
>  
> -		i40e_inc_ntp(rx_ring);
> -		rx_ring->next_to_clean = rx_ring->next_to_process;
> -		if (i40e_is_non_eop(rx_ring, rx_desc))
> -			continue;
> +			/* populate checksum, VLAN, and protocol */
> +			i40e_process_skb_fields(rx_ring, rx_desc, skb);
>  
> -		if (xdp_res || i40e_cleanup_headers(rx_ring, skb, rx_desc)) {
> -			skb = NULL;
> -			continue;
> +			i40e_trace(clean_rx_irq_rx, rx_ring, rx_desc, xdp);
> +			napi_gro_receive(&rx_ring->q_vector->napi, skb);
>  		}
>  
> -		/* probably a little skewed due to removing CRC */
> -		total_rx_bytes += skb->len;
> -
> -		/* populate checksum, VLAN, and protocol */
> -		i40e_process_skb_fields(rx_ring, rx_desc, skb);
> -
> -		i40e_trace(clean_rx_irq_rx, rx_ring, rx_desc, xdp);
> -		napi_gro_receive(&rx_ring->q_vector->napi, skb);
> -		skb = NULL;
> -
>  		/* update budget accounting */
>  		total_rx_packets++;
> +process_next:
> +		cleaned_count += nfrags + 1;
> +		i40e_put_rx_buffer(rx_ring, rx_buffer);
> +		rx_ring->next_to_clean = rx_ring->next_to_process;
> +
> +		xdp->data = NULL;
>  	}
>  
>  	i40e_finalize_xdp_rx(rx_ring, xdp_xmit);
> -	rx_ring->skb = skb;
>  
>  	i40e_update_rx_stats(rx_ring, total_rx_bytes, total_rx_packets);
>  
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.h b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> index e86abc25bb5e..14ad074639ab 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> @@ -393,14 +393,6 @@ struct i40e_ring {
>  
>  	struct rcu_head rcu;		/* to avoid race on free */
>  	u16 next_to_alloc;
> -	struct sk_buff *skb;		/* When i40e_clean_rx_ring_irq() must
> -					 * return before it sees the EOP for
> -					 * the current packet, we save that skb
> -					 * here and resume receiving this
> -					 * packet the next time
> -					 * i40e_clean_rx_ring_irq() is called
> -					 * for this ring.
> -					 */

this comment was valuable to me back when i was getting started with i40e,
so maybe we could have something equivalent around xdp_buff now?

>  	struct i40e_channel *ch;
>  	u16 rx_offset;
> -- 
> 2.34.1