Re: [PATCH v3 13/13] net/intel: add common Tx mbuf recycle

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, May 12, 2025 at 01:54:39PM +0100, Anatoly Burakov wrote:
> Currently, there are duplicate implementations of Tx mbuf recycle in some
> drivers, specifically ixgbe and i40e. Move them into a common header.
> 
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> ---
>  drivers/net/intel/common/recycle_mbufs.h      | 98 +++++++++++++++++++
>  drivers/net/intel/common/tx.h                 |  1 +
>  .../i40e/i40e_recycle_mbufs_vec_common.c      | 88 +----------------
>  .../ixgbe/ixgbe_recycle_mbufs_vec_common.c    | 89 +----------------
>  4 files changed, 107 insertions(+), 169 deletions(-)
> 
> diff --git a/drivers/net/intel/common/recycle_mbufs.h b/drivers/net/intel/common/recycle_mbufs.h
> index fd31c5c1ff..88779c5aa4 100644
> --- a/drivers/net/intel/common/recycle_mbufs.h
> +++ b/drivers/net/intel/common/recycle_mbufs.h
> @@ -64,4 +64,102 @@ ci_rx_recycle_mbufs(struct ci_rx_queue *rxq, const uint16_t nb_mbufs,
>  	rte_write32_wc_relaxed(rte_cpu_to_le_32(rx_id), rxq->qrx_tail);
>  }
>  
> +/**
> + * Recycle buffers on Tx. Note: the function must first perform a driver-specific
> + * DD-bit-set check to ensure that the Tx descriptors are ready for recycling.
> + *
> + * @param txq Tx queue pointer
> + * @param recycle_rxq_info recycling mbuf information
> + *
> + * @return how many buffers were recycled
> + */
> +static __rte_always_inline uint16_t
> +ci_tx_recycle_mbufs(struct ci_tx_queue *txq,
> +	struct rte_eth_recycle_rxq_info *recycle_rxq_info)
> +{
> +	struct ci_tx_entry *txep;
> +	struct rte_mbuf **rxep;
> +	int i, n;
> +	uint16_t nb_recycle_mbufs;
> +	uint16_t avail = 0;
> +	uint16_t mbuf_ring_size = recycle_rxq_info->mbuf_ring_size;
> +	uint16_t mask = recycle_rxq_info->mbuf_ring_size - 1;
> +	uint16_t refill_requirement = recycle_rxq_info->refill_requirement;
> +	uint16_t refill_head = *recycle_rxq_info->refill_head;
> +	uint16_t receive_tail = *recycle_rxq_info->receive_tail;
> +
> +	/* Get available recycling Rx buffers. */
> +	avail = (mbuf_ring_size - (refill_head - receive_tail)) & mask;
> +
> +	/* Check Tx free thresh and Rx available space. */
> +	if (txq->nb_tx_free > txq->tx_free_thresh || avail <= txq->tx_rs_thresh)
> +		return 0;
> +
> +	n = txq->tx_rs_thresh;
> +	nb_recycle_mbufs = n;
> +
> +	/* Mbufs recycle mode can only support no ring buffer wrapping around.
> +	 * Two case for this:
> +	 *
> +	 * case 1: The refill head of Rx buffer ring needs to be aligned with
> +	 * mbuf ring size. In this case, the number of Tx freeing buffers
> +	 * should be equal to refill_requirement.
> +	 *
> +	 * case 2: The refill head of Rx ring buffer does not need to be aligned
> +	 * with mbuf ring size. In this case, the update of refill head can not
> +	 * exceed the Rx mbuf ring size.
> +	 */
> +	if ((refill_requirement && refill_requirement != n) ||
> +		(!refill_requirement && (refill_head + n > mbuf_ring_size)))
> +		return 0;
> +
> +	/* First buffer to free from S/W ring is at index
> +	 * tx_next_dd - (tx_rs_thresh-1).
> +	 */
> +	txep = &txq->sw_ring[txq->tx_next_dd - (n - 1)];
> +	rxep = recycle_rxq_info->mbuf_ring;
> +	rxep += refill_head;
> +
> +	/* is fast-free enabled in offloads? */
> +	if (txq->offloads & RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE) {
> +		/* Avoid txq containing buffers from unexpected mempool. */
> +		if (unlikely(recycle_rxq_info->mp
> +					!= txep[0].mbuf->pool))
> +			return 0;
> +
> +		/* Directly put mbufs from Tx to Rx. */
> +		for (i = 0; i < n; i++)
> +			rxep[i] = txep[i].mbuf;
> +	} else {
> +		for (i = 0; i < n; i++) {
> +			rxep[i] = rte_pktmbuf_prefree_seg(txep[i].mbuf);
> +
> +			/* If Tx buffers are not the last reference or from
> +			 * unexpected mempool, previous copied buffers are
> +			 * considered as invalid.
> +			 */
> +			if (unlikely(rxep[i] == NULL ||
> +				recycle_rxq_info->mp != txep[i].mbuf->pool))
> +				nb_recycle_mbufs = 0;
> +		}
> +		/* If Tx buffers are not the last reference or
> +		 * from unexpected mempool, all recycled buffers
> +		 * are put into mempool.
> +		 */
> +		if (nb_recycle_mbufs == 0)
> +			for (i = 0; i < n; i++) {
> +				if (rxep[i] != NULL)
> +					rte_mempool_put(rxep[i]->pool, rxep[i]);
> +			}
> +	}
> +
> +	/* Update counters for Tx. */
> +	txq->nb_tx_free = (uint16_t)(txq->nb_tx_free + txq->tx_rs_thresh);
> +	txq->tx_next_dd = (uint16_t)(txq->tx_next_dd + txq->tx_rs_thresh);
> +	if (txq->tx_next_dd >= txq->nb_tx_desc)
> +		txq->tx_next_dd = (uint16_t)(txq->tx_rs_thresh - 1);
> +
> +	return nb_recycle_mbufs;
> +}
> +
>  #endif
> diff --git a/drivers/net/intel/common/tx.h b/drivers/net/intel/common/tx.h
> index c99bd5420f..cc70fa7db4 100644
> --- a/drivers/net/intel/common/tx.h
> +++ b/drivers/net/intel/common/tx.h
> @@ -37,6 +37,7 @@ struct ci_tx_queue {
>  		volatile struct ice_tx_desc *ice_tx_ring;
>  		volatile struct idpf_base_tx_desc *idpf_tx_ring;
>  		volatile union ixgbe_adv_tx_desc *ixgbe_tx_ring;
> +		volatile void *tx_ring; /**< Generic. */
>  	};
>  	volatile uint8_t *qtx_tail;               /* register address of tail */
>  	union {
> diff --git a/drivers/net/intel/i40e/i40e_recycle_mbufs_vec_common.c b/drivers/net/intel/i40e/i40e_recycle_mbufs_vec_common.c
> index 073357bee2..19edee781d 100644
> --- a/drivers/net/intel/i40e/i40e_recycle_mbufs_vec_common.c
> +++ b/drivers/net/intel/i40e/i40e_recycle_mbufs_vec_common.c
> @@ -23,92 +23,12 @@ i40e_recycle_tx_mbufs_reuse_vec(void *tx_queue,
>  	struct rte_eth_recycle_rxq_info *recycle_rxq_info)
>  {
>  	struct ci_tx_queue *txq = tx_queue;
> -	struct ci_tx_entry *txep;
> -	struct rte_mbuf **rxep;
> -	int i, n;
> -	uint16_t nb_recycle_mbufs;
> -	uint16_t avail = 0;
> -	uint16_t mbuf_ring_size = recycle_rxq_info->mbuf_ring_size;
> -	uint16_t mask = recycle_rxq_info->mbuf_ring_size - 1;
> -	uint16_t refill_requirement = recycle_rxq_info->refill_requirement;
> -	uint16_t refill_head = *recycle_rxq_info->refill_head;
> -	uint16_t receive_tail = *recycle_rxq_info->receive_tail;
> +	const uint64_t ctob = txq->i40e_tx_ring[txq->tx_next_dd].cmd_type_offset_bsz;
>  
> -	/* Get available recycling Rx buffers. */
> -	avail = (mbuf_ring_size - (refill_head - receive_tail)) & mask;
> -
> -	/* Check Tx free thresh and Rx available space. */
> -	if (txq->nb_tx_free > txq->tx_free_thresh || avail <= txq->tx_rs_thresh)
> -		return 0;
> -
> -	/* check DD bits on threshold descriptor */
> -	if ((txq->i40e_tx_ring[txq->tx_next_dd].cmd_type_offset_bsz &
> -				rte_cpu_to_le_64(I40E_TXD_QW1_DTYPE_MASK)) !=
> +	/* are Tx descriptors ready for recycling? */
> +	if ((ctob & rte_cpu_to_le_64(I40E_TXD_QW1_DTYPE_MASK)) !=
>  			rte_cpu_to_le_64(I40E_TX_DESC_DTYPE_DESC_DONE))
>  		return 0;

There is the function i40e_tx_desc_done (and similar functions for other
drivers) to do this check. In the tx cleanup code we pass that function in
as a callback - you could probably shorten things a little by doing so
here. Due to inlining, the indirect function call is eliminated by the
compiler (as constant propagation), leading to no perf penalty.

/Bruce