Re: [PATCH v3 5/7] net/mlx4: separate Tx segment cases

[Matan Azrad <matan@mellanox.com>]

Hi Adrien

> -----Original Message-----
> From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com]
> Sent: Monday, October 30, 2017 4:24 PM
> To: Matan Azrad <matan@mellanox.com>
> Cc: dev@dpdk.org; Ophir Munk <ophirmu@mellanox.com>
> Subject: Re: [PATCH v3 5/7] net/mlx4: separate Tx segment cases
> 
> 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?
> 
What's about next?
Optimize single segment case by processing it in different code which prevents checks and calculations relevant only to multi segment case. 

> > 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@mellanox.com>
> > Signed-off-by: Ophir Munk <ophirmu@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.
> 
Yes, you right, will be fixed in next version.

> > +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.
> 
OK.
> >  {
> >  	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()
> 
Good, thanks!

> > +{
> > +	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.
>

OK.
 
> > +
> 
> 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

Thanks!