From: Phil Yang <phil.yang@arm.com>
Date: Thu, 3 Sep 2020 02:53:10 +0000 (+0800)
Subject: net/mlx5: relax atomic refcnt for multi-packet Rx buffer
X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=ae3255bfd934be8f69ad4c960c755cddb817a12b;p=dpdk.git

net/mlx5: relax atomic refcnt for multi-packet Rx buffer

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@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Acked-by: Alexander Kozyrev <akozyrev@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
---

diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
index a9ccc2be8c..c059e216d4 100644
--- a/drivers/net/mlx5/mlx5_rxq.c
+++ b/drivers/net/mlx5/mlx5_rxq.c
@@ -1090,7 +1090,7 @@ 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 101555ed03..0b87be15b4 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 6876c1bc4a..9ffa028d2e 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[];
 	/*