Subject: Re: [PATCH net-next 4/4] igb: add AF_XDP zero-copy Tx support

From: Maciej Fijalkowski <[email-masked]>
Date: Sat, 10 Aug 2024 16:10:06 +0200

On Thu, Aug 08, 2024 at 11:35:54AM -0700, Tony Nguyen wrote:
> From: Sriram Yagnaraman <[email-masked]>
> 
> Add support for AF_XDP zero-copy transmit path.
> 
> A new TX buffer type IGB_TYPE_XSK is introduced to indicate that the Tx
> frame was allocated from the xsk buff pool, so igb_clean_tx_ring and
> igb_clean_tx_irq can clean the buffers correctly based on type.
> 
> igb_xmit_zc performs the actual packet transmit when AF_XDP zero-copy is
> enabled. We share the TX ring between slow path, XDP and AF_XDP
> zero-copy, so we use the netdev queue lock to ensure mutual exclusion.
> 
> Signed-off-by: Sriram Yagnaraman <[email-masked]>
> [Kurt: Set olinfo_status in igb_xmit_zc() so that frames are transmitted]
> Signed-off-by: Kurt Kanzenbach <[email-masked]>
> Tested-by: Chandan Kumar Rout <[email-masked]> (A Contingent Worker at Intel)
> Signed-off-by: Tony Nguyen <[email-masked]>
> ---
>  drivers/net/ethernet/intel/igb/igb.h      |  2 +
>  drivers/net/ethernet/intel/igb/igb_main.c | 56 +++++++++++++++++++----
>  drivers/net/ethernet/intel/igb/igb_xsk.c  | 53 +++++++++++++++++++++
>  3 files changed, 102 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb.h b/drivers/net/ethernet/intel/igb/igb.h
> index 4983a6ec718e..9ee18ac1ba47 100644
> --- a/drivers/net/ethernet/intel/igb/igb.h
> +++ b/drivers/net/ethernet/intel/igb/igb.h
> @@ -257,6 +257,7 @@ enum igb_tx_flags {
>  enum igb_tx_buf_type {
>  	IGB_TYPE_SKB = 0,
>  	IGB_TYPE_XDP,
> +	IGB_TYPE_XSK
>  };
>  
>  /* wrapper around a pointer to a socket buffer,
> @@ -836,6 +837,7 @@ int igb_xsk_pool_setup(struct igb_adapter *adapter,
>  bool igb_alloc_rx_buffers_zc(struct igb_ring *rx_ring, u16 count);
>  void igb_clean_rx_ring_zc(struct igb_ring *rx_ring);
>  int igb_clean_rx_irq_zc(struct igb_q_vector *q_vector, const int budget);
> +bool igb_xmit_zc(struct igb_ring *tx_ring);
>  int igb_xsk_wakeup(struct net_device *dev, u32 qid, u32 flags);
>  
>  #endif /* _IGB_H_ */
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
> index 0b779b2ca9ea..1ebd67981978 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -2996,6 +2996,9 @@ static int igb_xdp_xmit(struct net_device *dev, int n,
>  	if (unlikely(!tx_ring))
>  		return -ENXIO;
>  
> +	if (unlikely(test_bit(IGB_RING_FLAG_TX_DISABLED, &tx_ring->flags)))
> +		return -ENXIO;
> +
>  	nq = txring_txq(tx_ring);
>  	__netif_tx_lock(nq, cpu);
>  
> @@ -4917,15 +4920,20 @@ void igb_clean_tx_ring(struct igb_ring *tx_ring)
>  {
>  	u16 i = tx_ring->next_to_clean;
>  	struct igb_tx_buffer *tx_buffer = &tx_ring->tx_buffer_info[i];
> +	u32 xsk_frames = 0;
>  
>  	while (i != tx_ring->next_to_use) {
>  		union e1000_adv_tx_desc *eop_desc, *tx_desc;
>  
>  		/* Free all the Tx ring sk_buffs or xdp frames */
> -		if (tx_buffer->type == IGB_TYPE_SKB)
> +		if (tx_buffer->type == IGB_TYPE_SKB) {
>  			dev_kfree_skb_any(tx_buffer->skb);
> -		else
> +		} else if (tx_buffer->type == IGB_TYPE_XDP) {
>  			xdp_return_frame(tx_buffer->xdpf);
> +		} else if (tx_buffer->type == IGB_TYPE_XSK) {
> +			xsk_frames++;
> +			goto skip_for_xsk;
> +		}
>  
>  		/* unmap skb header data */
>  		dma_unmap_single(tx_ring->dev,
> @@ -4956,6 +4964,7 @@ void igb_clean_tx_ring(struct igb_ring *tx_ring)
>  					       DMA_TO_DEVICE);
>  		}
>  
> +skip_for_xsk:
>  		tx_buffer->next_to_watch = NULL;
>  
>  		/* move us one more past the eop_desc for start of next pkt */
> @@ -4970,6 +4979,9 @@ void igb_clean_tx_ring(struct igb_ring *tx_ring)
>  	/* reset BQL for queue */
>  	netdev_tx_reset_queue(txring_txq(tx_ring));
>  
> +	if (tx_ring->xsk_pool && xsk_frames)
> +		xsk_tx_completed(tx_ring->xsk_pool, xsk_frames);
> +
>  	/* reset next_to_use and next_to_clean */
>  	tx_ring->next_to_use = 0;
>  	tx_ring->next_to_clean = 0;
> @@ -6503,6 +6515,9 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
>  		return NETDEV_TX_BUSY;
>  	}
>  
> +	if (unlikely(test_bit(IGB_RING_FLAG_TX_DISABLED, &tx_ring->flags)))
> +		return NETDEV_TX_BUSY;
> +
>  	/* record the location of the first descriptor for this packet */
>  	first = &tx_ring->tx_buffer_info[tx_ring->next_to_use];
>  	first->type = IGB_TYPE_SKB;
> @@ -8263,13 +8278,17 @@ static int igb_poll(struct napi_struct *napi, int budget)
>   **/
>  static bool igb_clean_tx_irq(struct igb_q_vector *q_vector, int napi_budget)
>  {
> -	struct igb_adapter *adapter = q_vector->adapter;
> -	struct igb_ring *tx_ring = q_vector->tx.ring;
> -	struct igb_tx_buffer *tx_buffer;
> -	union e1000_adv_tx_desc *tx_desc;
>  	unsigned int total_bytes = 0, total_packets = 0;
> +	struct igb_adapter *adapter = q_vector->adapter;
>  	unsigned int budget = q_vector->tx.work_limit;
> +	struct igb_ring *tx_ring = q_vector->tx.ring;
>  	unsigned int i = tx_ring->next_to_clean;
> +	union e1000_adv_tx_desc *tx_desc;
> +	struct igb_tx_buffer *tx_buffer;
> +	int cpu = smp_processor_id();
> +	bool xsk_xmit_done = true;
> +	struct netdev_queue *nq;
> +	u32 xsk_frames = 0;
>  
>  	if (test_bit(__IGB_DOWN, &adapter->state))
>  		return true;
> @@ -8300,10 +8319,14 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector, int napi_budget)
>  		total_packets += tx_buffer->gso_segs;
>  
>  		/* free the skb */
> -		if (tx_buffer->type == IGB_TYPE_SKB)
> +		if (tx_buffer->type == IGB_TYPE_SKB) {
>  			napi_consume_skb(tx_buffer->skb, napi_budget);
> -		else
> +		} else if (tx_buffer->type == IGB_TYPE_XDP) {
>  			xdp_return_frame(tx_buffer->xdpf);
> +		} else if (tx_buffer->type == IGB_TYPE_XSK) {
> +			xsk_frames++;
> +			goto skip_for_xsk;
> +		}
>  
>  		/* unmap skb header data */
>  		dma_unmap_single(tx_ring->dev,
> @@ -8335,6 +8358,7 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector, int napi_budget)
>  			}
>  		}
>  
> +skip_for_xsk:
>  		/* move us one more past the eop_desc for start of next pkt */
>  		tx_buffer++;
>  		tx_desc++;
> @@ -8363,6 +8387,20 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector, int napi_budget)
>  	q_vector->tx.total_bytes += total_bytes;
>  	q_vector->tx.total_packets += total_packets;
>  
> +	if (tx_ring->xsk_pool) {

READ_ONCE()

> +		if (xsk_frames)
> +			xsk_tx_completed(tx_ring->xsk_pool, xsk_frames);
> +		if (xsk_uses_need_wakeup(tx_ring->xsk_pool))
> +			xsk_set_tx_need_wakeup(tx_ring->xsk_pool);
> +
> +		nq = txring_txq(tx_ring);
> +		__netif_tx_lock(nq, cpu);
> +		/* Avoid transmit queue timeout since we share it with the slow path */
> +		txq_trans_cond_update(nq);
> +		xsk_xmit_done = igb_xmit_zc(tx_ring);
> +		__netif_tx_unlock(nq);
> +	}
> +
>  	if (test_bit(IGB_RING_FLAG_TX_DETECT_HANG, &tx_ring->flags)) {
>  		struct e1000_hw *hw = &adapter->hw;
>  
> @@ -8425,7 +8463,7 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector, int napi_budget)
>  		}
>  	}
>  
> -	return !!budget;
> +	return !!budget && xsk_xmit_done;
>  }
>  
>  /**
> diff --git a/drivers/net/ethernet/intel/igb/igb_xsk.c b/drivers/net/ethernet/intel/igb/igb_xsk.c
> index 66cdc30e9b6e..4e530e1eb3c0 100644
> --- a/drivers/net/ethernet/intel/igb/igb_xsk.c
> +++ b/drivers/net/ethernet/intel/igb/igb_xsk.c
> @@ -431,6 +431,59 @@ int igb_clean_rx_irq_zc(struct igb_q_vector *q_vector, const int budget)
>  	return failure ? budget : (int)total_packets;
>  }
>  
> +bool igb_xmit_zc(struct igb_ring *tx_ring)
> +{
> +	unsigned int budget = igb_desc_unused(tx_ring);
> +	struct xsk_buff_pool *pool = tx_ring->xsk_pool;
> +	u32 cmd_type, olinfo_status, nb_pkts, i = 0;
> +	struct xdp_desc *descs = pool->tx_descs;
> +	union e1000_adv_tx_desc *tx_desc = NULL;
> +	struct igb_tx_buffer *tx_buffer_info;
> +	unsigned int total_bytes = 0;
> +	dma_addr_t dma;

check IGB_RING_FLAG_TX_DISABLED?

> +
> +	nb_pkts = xsk_tx_peek_release_desc_batch(pool, budget);
> +	if (!nb_pkts)
> +		return true;
> +
> +	while (nb_pkts-- > 0) {
> +		dma = xsk_buff_raw_get_dma(pool, descs[i].addr);
> +		xsk_buff_raw_dma_sync_for_device(pool, dma, descs[i].len);
> +
> +		tx_buffer_info = &tx_ring->tx_buffer_info[tx_ring->next_to_use];
> +		tx_buffer_info->bytecount = descs[i].len;
> +		tx_buffer_info->type = IGB_TYPE_XSK;
> +		tx_buffer_info->xdpf = NULL;
> +		tx_buffer_info->gso_segs = 1;
> +		tx_buffer_info->time_stamp = jiffies;
> +
> +		tx_desc = IGB_TX_DESC(tx_ring, tx_ring->next_to_use);
> +		tx_desc->read.buffer_addr = cpu_to_le64(dma);
> +
> +		/* put descriptor type bits */
> +		cmd_type = E1000_ADVTXD_DTYP_DATA | E1000_ADVTXD_DCMD_DEXT |
> +			   E1000_ADVTXD_DCMD_IFCS;
> +		olinfo_status = descs[i].len << E1000_ADVTXD_PAYLEN_SHIFT;
> +
> +		cmd_type |= descs[i].len | IGB_TXD_DCMD;

This is also sub-optimal as you are setting RS bit on each Tx descriptor,
which will in turn raise a lot of irqs. See how ice sets RS bit only on
last desc from a batch and then, on cleaning side, how it finds a
descriptor that is supposed to have DD bit written by HW.

> +		tx_desc->read.cmd_type_len = cpu_to_le32(cmd_type);
> +		tx_desc->read.olinfo_status = cpu_to_le32(olinfo_status);
> +
> +		total_bytes += descs[i].len;
> +
> +		i++;
> +		tx_ring->next_to_use++;
> +		tx_buffer_info->next_to_watch = tx_desc;
> +		if (tx_ring->next_to_use == tx_ring->count)
> +			tx_ring->next_to_use = 0;
> +	}
> +
> +	netdev_tx_sent_queue(txring_txq(tx_ring), total_bytes);
> +	igb_xdp_ring_update_tail(tx_ring);
> +
> +	return nb_pkts < budget;
> +}
> +
>  int igb_xsk_wakeup(struct net_device *dev, u32 qid, u32 flags)
>  {
>  	struct igb_adapter *adapter = netdev_priv(dev);
> -- 
> 2.42.0
>