[dpdk-dev] [PATCH v2 1/5] net/mlx5: change indexing for Tx SW ring

[Yongseok Koh <yskoh@mellanox.com>]

For Tx SW ring (txq->elts[]), indexes are kept and used in
txq->elts_head/tail. Because of this, one entry must always be left unused
and it also makes code complex. Changed to store counters instead of
indexes in order to make the code simpler and to reduce a few calculations.

Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
---
 drivers/net/mlx5/mlx5_rxtx.c | 108 +++++++++++++++++--------------------------
 drivers/net/mlx5/mlx5_rxtx.h |   4 +-
 drivers/net/mlx5/mlx5_txq.c  |  16 +++----
 3 files changed, 52 insertions(+), 76 deletions(-)

diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
index 70314b393..43db06ad8 100644
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -255,7 +255,8 @@ mlx5_copy_to_wq(void *dst, const void *src, size_t n,
 static inline void
 txq_complete(struct txq *txq)
 {
-	const unsigned int elts_n = 1 << txq->elts_n;
+	const uint16_t elts_n = 1 << txq->elts_n;
+	const uint16_t elts_m = elts_n - 1;
 	const unsigned int cqe_n = 1 << txq->cqe_n;
 	const unsigned int cqe_cnt = cqe_n - 1;
 	uint16_t elts_free = txq->elts_tail;
@@ -292,24 +293,23 @@ txq_complete(struct txq *txq)
 	ctrl = (volatile struct mlx5_wqe_ctrl *)
 		tx_mlx5_wqe(txq, txq->wqe_pi);
 	elts_tail = ctrl->ctrl3;
-	assert(elts_tail < (1 << txq->wqe_n));
+	assert((elts_tail & elts_m) < (1 << txq->wqe_n));
 	/* Free buffers. */
 	while (elts_free != elts_tail) {
-		struct rte_mbuf *elt = (*txq->elts)[elts_free];
-		unsigned int elts_free_next =
-			(elts_free + 1) & (elts_n - 1);
-		struct rte_mbuf *elt_next = (*txq->elts)[elts_free_next];
+		struct rte_mbuf *elt = (*txq->elts)[elts_free & elts_m];
+		struct rte_mbuf *elt_next =
+			(*txq->elts)[(elts_free + 1) & elts_m];
 
 #ifndef NDEBUG
 		/* Poisoning. */
-		memset(&(*txq->elts)[elts_free],
+		memset(&(*txq->elts)[elts_free & elts_m],
 		       0x66,
-		       sizeof((*txq->elts)[elts_free]));
+		       sizeof((*txq->elts)[elts_free & elts_m]));
 #endif
 		RTE_MBUF_PREFETCH_TO_FREE(elt_next);
 		/* Only one segment needs to be freed. */
 		rte_pktmbuf_free_seg(elt);
-		elts_free = elts_free_next;
+		++elts_free;
 	}
 	txq->cq_ci = cq_ci;
 	txq->elts_tail = elts_tail;
@@ -409,12 +409,10 @@ int
 mlx5_tx_descriptor_status(void *tx_queue, uint16_t offset)
 {
 	struct txq *txq = tx_queue;
-	const unsigned int elts_n = 1 << txq->elts_n;
-	const unsigned int elts_cnt = elts_n - 1;
-	unsigned int used;
+	uint16_t used;
 
 	txq_complete(txq);
-	used = (txq->elts_head - txq->elts_tail) & elts_cnt;
+	used = txq->elts_head - txq->elts_tail;
 	if (offset < used)
 		return RTE_ETH_TX_DESC_FULL;
 	return RTE_ETH_TX_DESC_DONE;
@@ -488,11 +486,12 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 {
 	struct txq *txq = (struct txq *)dpdk_txq;
 	uint16_t elts_head = txq->elts_head;
-	const unsigned int elts_n = 1 << txq->elts_n;
+	const uint16_t elts_n = 1 << txq->elts_n;
+	const uint16_t elts_m = elts_n - 1;
 	unsigned int i = 0;
 	unsigned int j = 0;
 	unsigned int k = 0;
-	unsigned int max;
+	uint16_t max_elts;
 	unsigned int max_inline = txq->max_inline;
 	const unsigned int inline_en = !!max_inline && txq->inline_en;
 	uint16_t max_wqe;
@@ -509,9 +508,7 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 	rte_prefetch0(*pkts);
 	/* Start processing. */
 	txq_complete(txq);
-	max = (elts_n - (elts_head - txq->elts_tail));
-	if (max > elts_n)
-		max -= elts_n;
+	max_elts = (elts_n - (elts_head - txq->elts_tail));
 	max_wqe = (1u << txq->wqe_n) - (txq->wqe_ci - txq->wqe_pi);
 	if (unlikely(!max_wqe))
 		return 0;
@@ -540,9 +537,9 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 		 * that one ring entry remains unused.
 		 */
 		assert(segs_n);
-		if (max < segs_n + 1)
+		if (max_elts < segs_n)
 			break;
-		max -= segs_n;
+		max_elts -= segs_n;
 		--segs_n;
 		if (unlikely(--max_wqe == 0))
 			break;
@@ -561,7 +558,7 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 		if (length < (MLX5_WQE_DWORD_SIZE + 2))
 			break;
 		/* Update element. */
-		(*txq->elts)[elts_head] = buf;
+		(*txq->elts)[elts_head & elts_m] = buf;
 		/* Prefetch next buffer data. */
 		if (pkts_n - i > 1)
 			rte_prefetch0(
@@ -801,8 +798,7 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 			naddr,
 			naddr >> 32,
 		};
-		elts_head = (elts_head + 1) & (elts_n - 1);
-		(*txq->elts)[elts_head] = buf;
+		(*txq->elts)[++elts_head & elts_m] = buf;
 		++sg;
 		/* Advance counter only if all segs are successfully posted. */
 		if (sg < segs_n)
@@ -810,7 +806,7 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 		else
 			j += sg;
 next_pkt:
-		elts_head = (elts_head + 1) & (elts_n - 1);
+		++elts_head;
 		++pkts;
 		++i;
 		/* Initialize known and common part of the WQE structure. */
@@ -853,7 +849,7 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 	/* Take a shortcut if nothing must be sent. */
 	if (unlikely((i + k) == 0))
 		return 0;
-	txq->elts_head = (txq->elts_head + i + j) & (elts_n - 1);
+	txq->elts_head += (i + j);
 	/* Check whether completion threshold has been reached. */
 	comp = txq->elts_comp + i + j + k;
 	if (comp >= MLX5_TX_COMP_THRESH) {
@@ -960,10 +956,11 @@ mlx5_tx_burst_mpw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 {
 	struct txq *txq = (struct txq *)dpdk_txq;
 	uint16_t elts_head = txq->elts_head;
-	const unsigned int elts_n = 1 << txq->elts_n;
+	const uint16_t elts_n = 1 << txq->elts_n;
+	const uint16_t elts_m = elts_n - 1;
 	unsigned int i = 0;
 	unsigned int j = 0;
-	unsigned int max;
+	uint16_t max_elts;
 	uint16_t max_wqe;
 	unsigned int comp;
 	struct mlx5_mpw mpw = {
@@ -977,15 +974,12 @@ mlx5_tx_burst_mpw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 	rte_prefetch0(tx_mlx5_wqe(txq, txq->wqe_ci + 1));
 	/* Start processing. */
 	txq_complete(txq);
-	max = (elts_n - (elts_head - txq->elts_tail));
-	if (max > elts_n)
-		max -= elts_n;
+	max_elts = (elts_n - (elts_head - txq->elts_tail));
 	max_wqe = (1u << txq->wqe_n) - (txq->wqe_ci - txq->wqe_pi);
 	if (unlikely(!max_wqe))
 		return 0;
 	do {
 		struct rte_mbuf *buf = *(pkts++);
-		unsigned int elts_head_next;
 		uint32_t length;
 		unsigned int segs_n = buf->nb_segs;
 		uint32_t cs_flags = 0;
@@ -995,12 +989,12 @@ mlx5_tx_burst_mpw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 		 * that one ring entry remains unused.
 		 */
 		assert(segs_n);
-		if (max < segs_n + 1)
+		if (max_elts < segs_n)
 			break;
 		/* Do not bother with large packets MPW cannot handle. */
 		if (segs_n > MLX5_MPW_DSEG_MAX)
 			break;
-		max -= segs_n;
+		max_elts -= segs_n;
 		--pkts_n;
 		/* Should we enable HW CKSUM offload */
 		if (buf->ol_flags &
@@ -1036,9 +1030,8 @@ mlx5_tx_burst_mpw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 			volatile struct mlx5_wqe_data_seg *dseg;
 			uintptr_t addr;
 
-			elts_head_next = (elts_head + 1) & (elts_n - 1);
 			assert(buf);
-			(*txq->elts)[elts_head] = buf;
+			(*txq->elts)[elts_head++ & elts_m] = buf;
 			dseg = mpw.data.dseg[mpw.pkts_n];
 			addr = rte_pktmbuf_mtod(buf, uintptr_t);
 			*dseg = (struct mlx5_wqe_data_seg){
@@ -1046,7 +1039,6 @@ mlx5_tx_burst_mpw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 				.lkey = txq_mp2mr(txq, txq_mb2mp(buf)),
 				.addr = htonll(addr),
 			};
-			elts_head = elts_head_next;
 #if defined(MLX5_PMD_SOFT_COUNTERS) || !defined(NDEBUG)
 			length += DATA_LEN(buf);
 #endif
@@ -1057,7 +1049,6 @@ mlx5_tx_burst_mpw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 		assert(length == mpw.len);
 		if (mpw.pkts_n == MLX5_MPW_DSEG_MAX)
 			mlx5_mpw_close(txq, &mpw);
-		elts_head = elts_head_next;
 #ifdef MLX5_PMD_SOFT_COUNTERS
 		/* Increment sent bytes counter. */
 		txq->stats.obytes += length;
@@ -1175,10 +1166,11 @@ mlx5_tx_burst_mpw_inline(void *dpdk_txq, struct rte_mbuf **pkts,
 {
 	struct txq *txq = (struct txq *)dpdk_txq;
 	uint16_t elts_head = txq->elts_head;
-	const unsigned int elts_n = 1 << txq->elts_n;
+	const uint16_t elts_n = 1 << txq->elts_n;
+	const uint16_t elts_m = elts_n - 1;
 	unsigned int i = 0;
 	unsigned int j = 0;
-	unsigned int max;
+	uint16_t max_elts;
 	uint16_t max_wqe;
 	unsigned int comp;
 	unsigned int inline_room = txq->max_inline * RTE_CACHE_LINE_SIZE;
@@ -1205,12 +1197,9 @@ mlx5_tx_burst_mpw_inline(void *dpdk_txq, struct rte_mbuf **pkts,
 	rte_prefetch0(tx_mlx5_wqe(txq, txq->wqe_ci + 1));
 	/* Start processing. */
 	txq_complete(txq);
-	max = (elts_n - (elts_head - txq->elts_tail));
-	if (max > elts_n)
-		max -= elts_n;
+	max_elts = (elts_n - (elts_head - txq->elts_tail));
 	do {
 		struct rte_mbuf *buf = *(pkts++);
-		unsigned int elts_head_next;
 		uintptr_t addr;
 		uint32_t length;
 		unsigned int segs_n = buf->nb_segs;
@@ -1221,12 +1210,12 @@ mlx5_tx_burst_mpw_inline(void *dpdk_txq, struct rte_mbuf **pkts,
 		 * that one ring entry remains unused.
 		 */
 		assert(segs_n);
-		if (max < segs_n + 1)
+		if (max_elts < segs_n)
 			break;
 		/* Do not bother with large packets MPW cannot handle. */
 		if (segs_n > MLX5_MPW_DSEG_MAX)
 			break;
-		max -= segs_n;
+		max_elts -= segs_n;
 		--pkts_n;
 		/*
 		 * Compute max_wqe in case less WQE were consumed in previous
@@ -1287,10 +1276,8 @@ mlx5_tx_burst_mpw_inline(void *dpdk_txq, struct rte_mbuf **pkts,
 			do {
 				volatile struct mlx5_wqe_data_seg *dseg;
 
-				elts_head_next =
-					(elts_head + 1) & (elts_n - 1);
 				assert(buf);
-				(*txq->elts)[elts_head] = buf;
+				(*txq->elts)[elts_head++ & elts_m] = buf;
 				dseg = mpw.data.dseg[mpw.pkts_n];
 				addr = rte_pktmbuf_mtod(buf, uintptr_t);
 				*dseg = (struct mlx5_wqe_data_seg){
@@ -1298,7 +1285,6 @@ mlx5_tx_burst_mpw_inline(void *dpdk_txq, struct rte_mbuf **pkts,
 					.lkey = txq_mp2mr(txq, txq_mb2mp(buf)),
 					.addr = htonll(addr),
 				};
-				elts_head = elts_head_next;
 #if defined(MLX5_PMD_SOFT_COUNTERS) || !defined(NDEBUG)
 				length += DATA_LEN(buf);
 #endif
@@ -1315,9 +1301,8 @@ mlx5_tx_burst_mpw_inline(void *dpdk_txq, struct rte_mbuf **pkts,
 			assert(mpw.state == MLX5_MPW_INL_STATE_OPENED);
 			assert(length <= inline_room);
 			assert(length == DATA_LEN(buf));
-			elts_head_next = (elts_head + 1) & (elts_n - 1);
 			addr = rte_pktmbuf_mtod(buf, uintptr_t);
-			(*txq->elts)[elts_head] = buf;
+			(*txq->elts)[elts_head++ & elts_m] = buf;
 			/* Maximum number of bytes before wrapping. */
 			max = ((((uintptr_t)(txq->wqes)) +
 				(1 << txq->wqe_n) *
@@ -1354,7 +1339,6 @@ mlx5_tx_burst_mpw_inline(void *dpdk_txq, struct rte_mbuf **pkts,
 				inline_room -= length;
 			}
 		}
-		elts_head = elts_head_next;
 #ifdef MLX5_PMD_SOFT_COUNTERS
 		/* Increment sent bytes counter. */
 		txq->stats.obytes += length;
@@ -1476,10 +1460,11 @@ mlx5_tx_burst_empw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 {
 	struct txq *txq = (struct txq *)dpdk_txq;
 	uint16_t elts_head = txq->elts_head;
-	const unsigned int elts_n = 1 << txq->elts_n;
+	const uint16_t elts_n = 1 << txq->elts_n;
+	const uint16_t elts_m = elts_n - 1;
 	unsigned int i = 0;
 	unsigned int j = 0;
-	unsigned int max_elts;
+	uint16_t max_elts;
 	uint16_t max_wqe;
 	unsigned int max_inline = txq->max_inline * RTE_CACHE_LINE_SIZE;
 	unsigned int mpw_room = 0;
@@ -1494,8 +1479,6 @@ mlx5_tx_burst_empw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 	/* Start processing. */
 	txq_complete(txq);
 	max_elts = (elts_n - (elts_head - txq->elts_tail));
-	if (max_elts > elts_n)
-		max_elts -= elts_n;
 	/* A CQE slot must always be available. */
 	assert((1u << txq->cqe_n) - (txq->cq_pi - txq->cq_ci));
 	max_wqe = (1u << txq->wqe_n) - (txq->wqe_ci - txq->wqe_pi);
@@ -1503,7 +1486,6 @@ mlx5_tx_burst_empw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 		return 0;
 	do {
 		struct rte_mbuf *buf = *(pkts++);
-		unsigned int elts_head_next;
 		uintptr_t addr;
 		uint64_t naddr;
 		unsigned int n;
@@ -1517,7 +1499,7 @@ mlx5_tx_burst_empw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 		 * that one ring entry remains unused.
 		 */
 		assert(segs_n);
-		if (max_elts - j < segs_n + 1)
+		if (max_elts - j < segs_n)
 			break;
 		/* Do not bother with large packets MPW cannot handle. */
 		if (segs_n > MLX5_MPW_DSEG_MAX)
@@ -1601,10 +1583,8 @@ mlx5_tx_burst_empw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 			do {
 				volatile struct mlx5_wqe_data_seg *dseg;
 
-				elts_head_next =
-					(elts_head + 1) & (elts_n - 1);
 				assert(buf);
-				(*txq->elts)[elts_head] = buf;
+				(*txq->elts)[elts_head++ & elts_m] = buf;
 				dseg = mpw.data.dseg[mpw.pkts_n];
 				addr = rte_pktmbuf_mtod(buf, uintptr_t);
 				*dseg = (struct mlx5_wqe_data_seg){
@@ -1612,7 +1592,6 @@ mlx5_tx_burst_empw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 					.lkey = txq_mp2mr(txq, txq_mb2mp(buf)),
 					.addr = htonll(addr),
 				};
-				elts_head = elts_head_next;
 #if defined(MLX5_PMD_SOFT_COUNTERS) || !defined(NDEBUG)
 				length += DATA_LEN(buf);
 #endif
@@ -1663,7 +1642,6 @@ mlx5_tx_burst_empw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 			/* No need to get completion as the entire packet is
 			 * copied to WQ. Free the buf right away.
 			 */
-			elts_head_next = elts_head;
 			rte_pktmbuf_free_seg(buf);
 			mpw_room -= (inl_pad + sizeof(inl_hdr) + length);
 			/* Add pad in the next packet if any. */
@@ -1686,8 +1664,7 @@ mlx5_tx_burst_empw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 				dseg = (volatile void *)
 					((uintptr_t)mpw.data.raw +
 					 inl_pad);
-			elts_head_next = (elts_head + 1) & (elts_n - 1);
-			(*txq->elts)[elts_head] = buf;
+			(*txq->elts)[elts_head++ & elts_m] = buf;
 			addr = rte_pktmbuf_mtod(buf, uintptr_t);
 			for (n = 0; n * RTE_CACHE_LINE_SIZE < length; n++)
 				rte_prefetch2((void *)(addr +
@@ -1706,7 +1683,6 @@ mlx5_tx_burst_empw(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
 			mpw_room -= (inl_pad + sizeof(*dseg));
 			inl_pad = 0;
 		}
-		elts_head = elts_head_next;
 #ifdef MLX5_PMD_SOFT_COUNTERS
 		/* Increment sent bytes counter. */
 		txq->stats.obytes += length;
diff --git a/drivers/net/mlx5/mlx5_rxtx.h b/drivers/net/mlx5/mlx5_rxtx.h
index 450a56966..f9b738b4e 100644
--- a/drivers/net/mlx5/mlx5_rxtx.h
+++ b/drivers/net/mlx5/mlx5_rxtx.h
@@ -242,8 +242,8 @@ struct hash_rxq {
 /* TX queue descriptor. */
 RTE_STD_C11
 struct txq {
-	uint16_t elts_head; /* Current index in (*elts)[]. */
-	uint16_t elts_tail; /* First element awaiting completion. */
+	uint16_t elts_head; /* Current counter in (*elts)[]. */
+	uint16_t elts_tail; /* Counter of first element awaiting completion. */
 	uint16_t elts_comp; /* Counter since last completion request. */
 	uint16_t mpw_comp; /* WQ index since last completion request. */
 	uint16_t cq_ci; /* Consumer index for completion queue. */
diff --git a/drivers/net/mlx5/mlx5_txq.c b/drivers/net/mlx5/mlx5_txq.c
index bf72468d5..f0729a2a8 100644
--- a/drivers/net/mlx5/mlx5_txq.c
+++ b/drivers/net/mlx5/mlx5_txq.c
@@ -103,9 +103,10 @@ txq_alloc_elts(struct txq_ctrl *txq_ctrl, unsigned int elts_n)
 static void
 txq_free_elts(struct txq_ctrl *txq_ctrl)
 {
-	unsigned int elts_n = 1 << txq_ctrl->txq.elts_n;
-	unsigned int elts_head = txq_ctrl->txq.elts_head;
-	unsigned int elts_tail = txq_ctrl->txq.elts_tail;
+	const uint16_t elts_n = 1 << txq_ctrl->txq.elts_n;
+	const uint16_t elts_m = elts_n - 1;
+	uint16_t elts_head = txq_ctrl->txq.elts_head;
+	uint16_t elts_tail = txq_ctrl->txq.elts_tail;
 	struct rte_mbuf *(*elts)[elts_n] = txq_ctrl->txq.elts;
 
 	DEBUG("%p: freeing WRs", (void *)txq_ctrl);
@@ -114,18 +115,17 @@ txq_free_elts(struct txq_ctrl *txq_ctrl)
 	txq_ctrl->txq.elts_comp = 0;
 
 	while (elts_tail != elts_head) {
-		struct rte_mbuf *elt = (*elts)[elts_tail];
+		struct rte_mbuf *elt = (*elts)[elts_tail & elts_m];
 
 		assert(elt != NULL);
 		rte_pktmbuf_free_seg(elt);
 #ifndef NDEBUG
 		/* Poisoning. */
-		memset(&(*elts)[elts_tail],
+		memset(&(*elts)[elts_tail & elts_m],
 		       0x77,
-		       sizeof((*elts)[elts_tail]));
+		       sizeof((*elts)[elts_tail & elts_m]));
 #endif
-		if (++elts_tail == elts_n)
-			elts_tail = 0;
+		++elts_tail;
 	}
 }
 
-- 
2.11.0