[dpdk-dev] [PATCH v4] net/mlx5: relaxed ordering for multi-packet RQ buffer refcnt

Phil Yang phil.yang at arm.com
Thu Sep 3 04:53:10 CEST 2020


Use c11 atomics with RELAXED ordering instead of the rte_atomic ops
which enforce unnecessary barriers on aarch64.

Signed-off-by: Phil Yang <phil.yang at arm.com>
---
v4:
Remove the unnecessary ACQUIRE barrier in rx burst path. (Honnappa)

v3:
Split from the patchset:
http://patchwork.dpdk.org/cover/68159/

 drivers/net/mlx5/mlx5_rxq.c  |  2 +-
 drivers/net/mlx5/mlx5_rxtx.c | 16 +++++++++-------
 drivers/net/mlx5/mlx5_rxtx.h |  2 +-
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
index 79eb8f8..40e0239 100644
--- a/drivers/net/mlx5/mlx5_rxq.c
+++ b/drivers/net/mlx5/mlx5_rxq.c
@@ -2012,7 +2012,7 @@ mlx5_mprq_buf_init(struct rte_mempool *mp, void *opaque_arg,
 
 	memset(_m, 0, sizeof(*buf));
 	buf->mp = mp;
-	rte_atomic16_set(&buf->refcnt, 1);
+	__atomic_store_n(&buf->refcnt, 1, __ATOMIC_RELAXED);
 	for (j = 0; j != strd_n; ++j) {
 		shinfo = &buf->shinfos[j];
 		shinfo->free_cb = mlx5_mprq_buf_free_cb;
diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
index 1b71e94..549477b 100644
--- a/drivers/net/mlx5/mlx5_rxtx.c
+++ b/drivers/net/mlx5/mlx5_rxtx.c
@@ -1626,10 +1626,11 @@ mlx5_mprq_buf_free_cb(void *addr __rte_unused, void *opaque)
 {
 	struct mlx5_mprq_buf *buf = opaque;
 
-	if (rte_atomic16_read(&buf->refcnt) == 1) {
+	if (__atomic_load_n(&buf->refcnt, __ATOMIC_RELAXED) == 1) {
 		rte_mempool_put(buf->mp, buf);
-	} else if (rte_atomic16_add_return(&buf->refcnt, -1) == 0) {
-		rte_atomic16_set(&buf->refcnt, 1);
+	} else if (unlikely(__atomic_sub_fetch(&buf->refcnt, 1,
+					       __ATOMIC_RELAXED) == 0)) {
+		__atomic_store_n(&buf->refcnt, 1, __ATOMIC_RELAXED);
 		rte_mempool_put(buf->mp, buf);
 	}
 }
@@ -1709,7 +1710,8 @@ mlx5_rx_burst_mprq(void *dpdk_rxq, struct rte_mbuf **pkts, uint16_t pkts_n)
 
 		if (consumed_strd == strd_n) {
 			/* Replace WQE only if the buffer is still in use. */
-			if (rte_atomic16_read(&buf->refcnt) > 1) {
+			if (__atomic_load_n(&buf->refcnt,
+					    __ATOMIC_RELAXED) > 1) {
 				mprq_buf_replace(rxq, rq_ci & wq_mask, strd_n);
 				/* Release the old buffer. */
 				mlx5_mprq_buf_free(buf);
@@ -1821,9 +1823,9 @@ mlx5_rx_burst_mprq(void *dpdk_rxq, struct rte_mbuf **pkts, uint16_t pkts_n)
 			void *buf_addr;
 
 			/* Increment the refcnt of the whole chunk. */
-			rte_atomic16_add_return(&buf->refcnt, 1);
-			MLX5_ASSERT((uint16_t)rte_atomic16_read(&buf->refcnt) <=
-				    strd_n + 1);
+			__atomic_add_fetch(&buf->refcnt, 1, __ATOMIC_RELAXED);
+			MLX5_ASSERT(__atomic_load_n(&buf->refcnt,
+				    __ATOMIC_RELAXED) <= strd_n + 1);
 			buf_addr = RTE_PTR_SUB(addr, RTE_PKTMBUF_HEADROOM);
 			/*
 			 * MLX5 device doesn't use iova but it is necessary in a
diff --git a/drivers/net/mlx5/mlx5_rxtx.h b/drivers/net/mlx5/mlx5_rxtx.h
index c02a007..467f31d 100644
--- a/drivers/net/mlx5/mlx5_rxtx.h
+++ b/drivers/net/mlx5/mlx5_rxtx.h
@@ -68,7 +68,7 @@ struct rxq_zip {
 /* Multi-Packet RQ buffer header. */
 struct mlx5_mprq_buf {
 	struct rte_mempool *mp;
-	rte_atomic16_t refcnt; /* Atomically accessed refcnt. */
+	uint16_t refcnt; /* Atomically accessed refcnt. */
 	uint8_t pad[RTE_PKTMBUF_HEADROOM]; /* Headroom for the first packet. */
 	struct rte_mbuf_ext_shared_info shinfos[];
 	/*
-- 
2.7.4



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