[dpdk-dev] [PATCH v3 5/7] net/mlx4: separate Tx segment cases

[Adrien Mazarguil]

On Mon, Oct 30, 2017 at 10:07:27AM +0000, Matan Azrad wrote:
> Since single segment packets shouldn't use additional memory to
> save segments byte count we can prevent additional memory
> unnecessary usage in this case; Prevent loop management.
> 

Sorry for asking but I really don't understand the above, can you
reformulate the problem addressed by this patch?

> Call a dedicated function for handling multi segments case.

This sentence is clearer, I'll base my review on what this patch does, not
the reasons behind it.

> Signed-off-by: Matan Azrad <matan at mellanox.com>
> Signed-off-by: Ophir Munk <ophirmu at mellanox.com>
> ---
>  drivers/net/mlx4/mlx4_rxtx.c | 247 +++++++++++++++++++++++++++----------------
>  1 file changed, 158 insertions(+), 89 deletions(-)
> 
> diff --git a/drivers/net/mlx4/mlx4_rxtx.c b/drivers/net/mlx4/mlx4_rxtx.c
> index 8ce70d6..8ea8851 100644
> --- a/drivers/net/mlx4/mlx4_rxtx.c
> +++ b/drivers/net/mlx4/mlx4_rxtx.c
> @@ -62,6 +62,9 @@
>  #include "mlx4_rxtx.h"
>  #include "mlx4_utils.h"
>  
> +#define WQE_ONE_DATA_SEG_SIZE \
> +	(sizeof(struct mlx4_wqe_ctrl_seg) + sizeof(struct mlx4_wqe_data_seg))
> +
>  /**
>   * Pointer-value pair structure used in tx_post_send for saving the first
>   * DWORD (32 byte) of a TXBB.
> @@ -140,22 +143,19 @@ struct pv {
>   * @return
>   *   0 on success, -1 on failure.
>   */
> -static int
> -mlx4_txq_complete(struct txq *txq)
> +static inline int

While likely harmless, I think the addition of this inline keyword is not
related to this patch.

> +mlx4_txq_complete(struct txq *txq, const unsigned int elts_n,
> +				struct mlx4_sq *sq)

Looks like an indentation issue, you should align it to the contents of the
opening "(" to match the coding style of this file.

>  {
>  	unsigned int elts_comp = txq->elts_comp;
>  	unsigned int elts_tail = txq->elts_tail;
> -	const unsigned int elts_n = txq->elts_n;
>  	struct mlx4_cq *cq = &txq->mcq;
> -	struct mlx4_sq *sq = &txq->msq;
>  	struct mlx4_cqe *cqe;
>  	uint32_t cons_index = cq->cons_index;
>  	uint16_t new_index;
>  	uint16_t nr_txbbs = 0;
>  	int pkts = 0;
>  
> -	if (unlikely(elts_comp == 0))
> -		return 0;
>  	/*
>  	 * Traverse over all CQ entries reported and handle each WQ entry
>  	 * reported by them.
> @@ -238,6 +238,122 @@ struct pv {
>  	return buf->pool;
>  }
>  
> +static int handle_multi_segs(struct rte_mbuf *buf,
> +			    struct txq *txq,
> +			    struct mlx4_wqe_ctrl_seg **pctrl)

How about naming this function in a way that follows the mlx4_something()
convention?

Here's a suggestion based on how this function remains tied to
mlx4_tx_burst():

 mlx4_tx_burst_seg()

> +{
> +	int wqe_real_size;
> +	int nr_txbbs;
> +	struct pv *pv = (struct pv *)txq->bounce_buf;
> +	struct mlx4_sq *sq = &txq->msq;
> +	uint32_t head_idx = sq->head & sq->txbb_cnt_mask;
> +	struct mlx4_wqe_ctrl_seg *ctrl;
> +	struct mlx4_wqe_data_seg *dseg;
> +	uint32_t lkey;
> +	uintptr_t addr;
> +	uint32_t byte_count;
> +	int pv_counter = 0;
> +
> +	/* Calculate the needed work queue entry size for this packet. */
> +	wqe_real_size = sizeof(struct mlx4_wqe_ctrl_seg) +
> +		buf->nb_segs * sizeof(struct mlx4_wqe_data_seg);
> +	nr_txbbs = MLX4_SIZE_TO_TXBBS(wqe_real_size);
> +	/*
> +	 * Check that there is room for this WQE in the send queue and that
> +	 * the WQE size is legal.
> +	 */
> +	if (((sq->head - sq->tail) + nr_txbbs +
> +				sq->headroom_txbbs) >= sq->txbb_cnt ||
> +			nr_txbbs > MLX4_MAX_WQE_TXBBS) {
> +		return -1;
> +	}
> +

Extra empty line.

> +	/* Get the control and data entries of the WQE. */
> +	ctrl = (struct mlx4_wqe_ctrl_seg *)mlx4_get_send_wqe(sq, head_idx);
> +	dseg = (struct mlx4_wqe_data_seg *)((uintptr_t)ctrl +
> +			sizeof(struct mlx4_wqe_ctrl_seg));
> +	*pctrl = ctrl;
> +	/* Fill the data segments with buffer information. */
> +	struct rte_mbuf *sbuf;

I'm usually fine with mixing declarations and code when there's a good
reason, however in this case there's no point. sbuf could have been defined
with the rest at the beginning of the function.

> +

Extra empty line here as well.

> +	for (sbuf = buf; sbuf != NULL; sbuf = sbuf->next, dseg++) {
> +		addr = rte_pktmbuf_mtod(sbuf, uintptr_t);
> +		rte_prefetch0((volatile void *)addr);
> +		/* Handle WQE wraparound. */
> +		if (dseg >= (struct mlx4_wqe_data_seg *)sq->eob)
> +			dseg = (struct mlx4_wqe_data_seg *)sq->buf;
> +		dseg->addr = rte_cpu_to_be_64(addr);
> +		/* Memory region key (big endian) for this memory pool. */
> +		lkey = mlx4_txq_mp2mr(txq, mlx4_txq_mb2mp(sbuf));
> +		dseg->lkey = rte_cpu_to_be_32(lkey);
> +#ifndef NDEBUG
> +		/* Calculate the needed work queue entry size for this packet */
> +		if (unlikely(dseg->lkey == rte_cpu_to_be_32((uint32_t)-1))) {
> +			/* MR does not exist. */
> +			DEBUG("%p: unable to get MP <-> MR association",
> +					(void *)txq);
> +			/*
> +			 * Restamp entry in case of failure.
> +			 * Make sure that size is written correctly
> +			 * Note that we give ownership to the SW, not the HW.
> +			 */
> +			wqe_real_size = sizeof(struct mlx4_wqe_ctrl_seg) +
> +				buf->nb_segs * sizeof(struct mlx4_wqe_data_seg);
> +			ctrl->fence_size = (wqe_real_size >> 4) & 0x3f;
> +			mlx4_txq_stamp_freed_wqe(sq, head_idx,
> +					(sq->head & sq->txbb_cnt) ? 0 : 1);
> +			return -1;
> +		}
> +#endif /* NDEBUG */
> +		if (likely(sbuf->data_len)) {
> +			byte_count = rte_cpu_to_be_32(sbuf->data_len);
> +		} else {
> +			/*
> +			 * Zero length segment is treated as inline segment
> +			 * with zero data.
> +			 */
> +			byte_count = RTE_BE32(0x80000000);
> +		}
> +		/*
> +		 * If the data segment is not at the beginning of a
> +		 * Tx basic block (TXBB) then write the byte count,
> +		 * else postpone the writing to just before updating the
> +		 * control segment.
> +		 */
> +		if ((uintptr_t)dseg & (uintptr_t)(MLX4_TXBB_SIZE - 1)) {
> +			/*
> +			 * Need a barrier here before writing the byte_count
> +			 * fields to make sure that all the data is visible
> +			 * before the byte_count field is set.
> +			 * Otherwise, if the segment begins a new cacheline,
> +			 * the HCA prefetcher could grab the 64-byte chunk and
> +			 * get a valid (!= 0xffffffff) byte count but stale
> +			 * data, and end up sending the wrong data.
> +			 */
> +			rte_io_wmb();
> +			dseg->byte_count = byte_count;
> +		} else {
> +			/*
> +			 * This data segment starts at the beginning of a new
> +			 * TXBB, so we need to postpone its byte_count writing
> +			 * for later.
> +			 */
> +			pv[pv_counter].dseg = dseg;
> +			pv[pv_counter++].val = byte_count;
> +		}
> +	}
> +	/* Write the first DWORD of each TXBB save earlier. */
> +	if (pv_counter) {
> +		/* Need a barrier here before writing the byte_count. */
> +		rte_io_wmb();
> +		for (--pv_counter; pv_counter  >= 0; pv_counter--)
> +			pv[pv_counter].dseg->byte_count = pv[pv_counter].val;
> +	}
> +	/* Fill the control parameters for this packet. */
> +	ctrl->fence_size = (wqe_real_size >> 4) & 0x3f;
> +

Extra empty line.

> +	return nr_txbbs;
> +}
>  /**
>   * DPDK callback for Tx.
>   *
> @@ -261,10 +377,11 @@ struct pv {
>  	unsigned int i;
>  	unsigned int max;
>  	struct mlx4_sq *sq = &txq->msq;
> -	struct pv *pv = (struct pv *)txq->bounce_buf;
> +	int nr_txbbs;
>  
>  	assert(txq->elts_comp_cd != 0);
> -	mlx4_txq_complete(txq);
> +	if (likely(txq->elts_comp != 0))
> +		mlx4_txq_complete(txq, elts_n, sq);
>  	max = (elts_n - (elts_head - txq->elts_tail));
>  	if (max > elts_n)
>  		max -= elts_n;
> @@ -283,7 +400,6 @@ struct pv {
>  		uint32_t owner_opcode = MLX4_OPCODE_SEND;
>  		struct mlx4_wqe_ctrl_seg *ctrl;
>  		struct mlx4_wqe_data_seg *dseg;
> -		struct rte_mbuf *sbuf;
>  		union {
>  			uint32_t flags;
>  			uint16_t flags16[2];
> @@ -291,10 +407,6 @@ struct pv {
>  		uint32_t head_idx = sq->head & sq->txbb_cnt_mask;
>  		uint32_t lkey;
>  		uintptr_t addr;
> -		uint32_t byte_count;
> -		int wqe_real_size;
> -		int nr_txbbs;
> -		int pv_counter = 0;
>  
>  		/* Clean up old buffer. */
>  		if (likely(elt->buf != NULL)) {
> @@ -313,40 +425,29 @@ struct pv {
>  			} while (tmp != NULL);
>  		}
>  		RTE_MBUF_PREFETCH_TO_FREE(elt_next->buf);
> -
> -		/*
> -		 * Calculate the needed work queue entry size
> -		 * for this packet.
> -		 */
> -		wqe_real_size = sizeof(struct mlx4_wqe_ctrl_seg) +
> -				buf->nb_segs * sizeof(struct mlx4_wqe_data_seg);
> -		nr_txbbs = MLX4_SIZE_TO_TXBBS(wqe_real_size);
> -		/*
> -		 * Check that there is room for this WQE in the send
> -		 * queue and that the WQE size is legal.
> -		 */
> -		if (((sq->head - sq->tail) + nr_txbbs +
> -		     sq->headroom_txbbs) >= sq->txbb_cnt ||
> -		    nr_txbbs > MLX4_MAX_WQE_TXBBS) {
> -			elt->buf = NULL;
> -			break;
> -		}
> -		/* Get the control and data entries of the WQE. */
> -		ctrl = (struct mlx4_wqe_ctrl_seg *)
> -				mlx4_get_send_wqe(sq, head_idx);
> -		dseg = (struct mlx4_wqe_data_seg *)((uintptr_t)ctrl +
> -				sizeof(struct mlx4_wqe_ctrl_seg));
> -		/* Fill the data segments with buffer information. */
> -		for (sbuf = buf; sbuf != NULL; sbuf = sbuf->next, dseg++) {
> -			addr = rte_pktmbuf_mtod(sbuf, uintptr_t);
> +		if (buf->nb_segs == 1) {
> +			/*
> +			 * Check that there is room for this WQE in the send
> +			 * queue and that the WQE size is legal
> +			 */
> +			if (((sq->head - sq->tail) + 1 + sq->headroom_txbbs) >=
> +			     sq->txbb_cnt || 1 > MLX4_MAX_WQE_TXBBS) {
> +				elt->buf = NULL;
> +				break;
> +			}
> +			/* Get the control and data entries of the WQE. */
> +			ctrl = (struct mlx4_wqe_ctrl_seg *)
> +					mlx4_get_send_wqe(sq, head_idx);
> +			dseg = (struct mlx4_wqe_data_seg *)((uintptr_t)ctrl +
> +					sizeof(struct mlx4_wqe_ctrl_seg));
> +			addr = rte_pktmbuf_mtod(buf, uintptr_t);
>  			rte_prefetch0((volatile void *)addr);
>  			/* Handle WQE wraparound. */
> -			if (unlikely(dseg >=
> -			    (struct mlx4_wqe_data_seg *)sq->eob))
> +			if (dseg >= (struct mlx4_wqe_data_seg *)sq->eob)

Ideally this change should have been on its own in a fix commit.

>  				dseg = (struct mlx4_wqe_data_seg *)sq->buf;
>  			dseg->addr = rte_cpu_to_be_64(addr);
>  			/* Memory region key (big endian). */
> -			lkey = mlx4_txq_mp2mr(txq, mlx4_txq_mb2mp(sbuf));
> +			lkey = mlx4_txq_mp2mr(txq, mlx4_txq_mb2mp(buf));
>  			dseg->lkey = rte_cpu_to_be_32(lkey);
>  #ifndef NDEBUG
>  			if (unlikely(dseg->lkey ==
> @@ -360,61 +461,28 @@ struct pv {
>  				 * Note that we give ownership to the SW,
>  				 * not the HW.
>  				 */
> -				ctrl->fence_size = (wqe_real_size >> 4) & 0x3f;
> +				ctrl->fence_size =
> +					(WQE_ONE_DATA_SEG_SIZE >> 4) & 0x3f;
>  				mlx4_txq_stamp_freed_wqe(sq, head_idx,
>  					     (sq->head & sq->txbb_cnt) ? 0 : 1);
>  				elt->buf = NULL;
>  				break;
>  			}
>  #endif /* NDEBUG */
> -			if (likely(sbuf->data_len)) {
> -				byte_count = rte_cpu_to_be_32(sbuf->data_len);
> -			} else {
> -				/*
> -				 * Zero length segment is treated as inline
> -				 * segment with zero data.
> -				 */
> -				byte_count = RTE_BE32(0x80000000);
> -			}
> -			/*
> -			 * If the data segment is not at the beginning
> -			 * of a Tx basic block (TXBB) then write the
> -			 * byte count, else postpone the writing to
> -			 * just before updating the control segment.
> -			 */
> -			if ((uintptr_t)dseg & (uintptr_t)(MLX4_TXBB_SIZE - 1)) {
> -				/*
> -				 * Need a barrier here before writing the
> -				 * byte_count fields to make sure that all the
> -				 * data is visible before the byte_count field
> -				 * is set. otherwise, if the segment begins a
> -				 * new cacheline, the HCA prefetcher could grab
> -				 * the 64-byte chunk and get a valid
> -				 * (!= 0xffffffff) byte count but stale data,
> -				 * and end up sending the wrong data.
> -				 */
> -				rte_io_wmb();
> -				dseg->byte_count = byte_count;
> -			} else {
> -				/*
> -				 * This data segment starts at the beginning of
> -				 * a new TXBB, so we need to postpone its
> -				 * byte_count writing for later.
> -				 */
> -				pv[pv_counter].dseg = dseg;
> -				pv[pv_counter++].val = byte_count;
> -			}
> -		}
> -		/* Write the first DWORD of each TXBB save earlier. */
> -		if (pv_counter) {
> -			/* Need a barrier before writing the byte_count. */
> +			/* Need a barrier here before byte count store. */
>  			rte_io_wmb();
> -			for (--pv_counter; pv_counter  >= 0; pv_counter--)
> -				pv[pv_counter].dseg->byte_count =
> -						pv[pv_counter].val;
> +			dseg->byte_count = rte_cpu_to_be_32(buf->data_len);
> +

Extra empty line.

> +			/* Fill the control parameters for this packet. */
> +			ctrl->fence_size = (WQE_ONE_DATA_SEG_SIZE >> 4) & 0x3f;
> +			nr_txbbs = 1;
> +		} else {
> +			nr_txbbs = handle_multi_segs(buf, txq, &ctrl);
> +			if (nr_txbbs < 0) {
> +				elt->buf = NULL;
> +				break;
> +			}
>  		}
> -		/* Fill the control parameters for this packet. */
> -		ctrl->fence_size = (wqe_real_size >> 4) & 0x3f;
>  		/*
>  		 * For raw Ethernet, the SOLICIT flag is used to indicate
>  		 * that no ICRC should be calculated.
> @@ -469,6 +537,7 @@ struct pv {
>  		ctrl->owner_opcode = rte_cpu_to_be_32(owner_opcode |
>  					      ((sq->head & sq->txbb_cnt) ?
>  						       MLX4_BIT_WQE_OWN : 0));
> +

Extra empty line.

>  		sq->head += nr_txbbs;
>  		elt->buf = buf;
>  		bytes_sent += buf->pkt_len;
> -- 
> 1.8.3.1
> 

-- 
Adrien Mazarguil
6WIND