[Patch v4] net/mana: use rte_pktmbuf_alloc_bulk for allocating RX mbufs

[longli@linuxonhyperv.com]

From: Long Li <longli@microsoft.com>

Instead of allocating mbufs one by one during RX, use
rte_pktmbuf_alloc_bulk() to allocate them in a batch.

With this patch, there are no measurable performance improvements in
benchmarks. However, this patch should improve CPU cycles and reduce
potential locking conflicts in real-world applications.

Signed-off-by: Long Li <longli@microsoft.com>
---
Change in v2:
use rte_calloc_socket() in place of rte_calloc()

v3:
add more comment explaining the benefit of doing alloc_bulk.
free mbufs that are failed to post

v4:
replace rte_calloc_socket() with a fixed array on the stack

 drivers/net/mana/rx.c | 76 ++++++++++++++++++++++++++++---------------
 1 file changed, 50 insertions(+), 26 deletions(-)

diff --git a/drivers/net/mana/rx.c b/drivers/net/mana/rx.c
index acad5e26cd..4fc0f789d8 100644
--- a/drivers/net/mana/rx.c
+++ b/drivers/net/mana/rx.c
@@ -59,9 +59,8 @@ mana_rq_ring_doorbell(struct mana_rxq *rxq)
 }
 
 static int
-mana_alloc_and_post_rx_wqe(struct mana_rxq *rxq)
+mana_post_rx_wqe(struct mana_rxq *rxq, struct rte_mbuf *mbuf)
 {
-	struct rte_mbuf *mbuf = NULL;
 	struct gdma_sgl_element sgl[1];
 	struct gdma_work_request request;
 	uint32_t wqe_size_in_bu;
@@ -69,12 +68,6 @@ mana_alloc_and_post_rx_wqe(struct mana_rxq *rxq)
 	int ret;
 	struct mana_mr_cache *mr;
 
-	mbuf = rte_pktmbuf_alloc(rxq->mp);
-	if (!mbuf) {
-		rxq->stats.nombuf++;
-		return -ENOMEM;
-	}
-
 	mr = mana_alloc_pmd_mr(&rxq->mr_btree, priv, mbuf);
 	if (!mr) {
 		DP_LOG(ERR, "failed to register RX MR");
@@ -120,20 +113,33 @@ mana_alloc_and_post_rx_wqe(struct mana_rxq *rxq)
 /*
  * Post work requests for a Rx queue.
  */
+#define MANA_MBUF_BULK 32u
 static int
-mana_alloc_and_post_rx_wqes(struct mana_rxq *rxq)
+mana_alloc_and_post_rx_wqes(struct mana_rxq *rxq, uint32_t count)
 {
 	int ret;
-	uint32_t i;
+	uint32_t i, batch_count;
+	struct rte_mbuf *mbufs[MANA_MBUF_BULK];
+
+more_mbufs:
+	batch_count = RTE_MIN(count, MANA_MBUF_BULK);
+	ret = rte_pktmbuf_alloc_bulk(rxq->mp, mbufs, batch_count);
+	if (ret) {
+		DP_LOG(ERR, "failed to allocate mbufs for RX");
+		rxq->stats.nombuf += count;
+
+		/* Bail out to ring doorbell for posted packets */
+		goto out;
+	}
 
 #ifdef RTE_ARCH_32
 	rxq->wqe_cnt_to_short_db = 0;
 #endif
-	for (i = 0; i < rxq->num_desc; i++) {
-		ret = mana_alloc_and_post_rx_wqe(rxq);
+	for (i = 0; i < batch_count; i++) {
+		ret = mana_post_rx_wqe(rxq, mbufs[i]);
 		if (ret) {
 			DP_LOG(ERR, "failed to post RX ret = %d", ret);
-			return ret;
+			break;
 		}
 
 #ifdef RTE_ARCH_32
@@ -144,8 +150,15 @@ mana_alloc_and_post_rx_wqes(struct mana_rxq *rxq)
 #endif
 	}
 
-	mana_rq_ring_doorbell(rxq);
+	/* Free the remaining mbufs that are not posted */
+	rte_pktmbuf_free_bulk(&mbufs[i], batch_count - i);
+
+	count -= batch_count;
+	if (count > 0)
+		goto more_mbufs;
 
+out:
+	mana_rq_ring_doorbell(rxq);
 	return ret;
 }
 
@@ -404,7 +417,9 @@ mana_start_rx_queues(struct rte_eth_dev *dev)
 	}
 
 	for (i = 0; i < priv->num_queues; i++) {
-		ret = mana_alloc_and_post_rx_wqes(dev->data->rx_queues[i]);
+		struct mana_rxq *rxq = dev->data->rx_queues[i];
+
+		ret = mana_alloc_and_post_rx_wqes(rxq, rxq->num_desc);
 		if (ret)
 			goto fail;
 	}
@@ -423,7 +438,7 @@ uint16_t
 mana_rx_burst(void *dpdk_rxq, struct rte_mbuf **pkts, uint16_t pkts_n)
 {
 	uint16_t pkt_received = 0;
-	uint16_t wqe_posted = 0;
+	uint16_t wqe_consumed = 0;
 	struct mana_rxq *rxq = dpdk_rxq;
 	struct mana_priv *priv = rxq->priv;
 	struct rte_mbuf *mbuf;
@@ -535,18 +550,23 @@ mana_rx_burst(void *dpdk_rxq, struct rte_mbuf **pkts, uint16_t pkts_n)
 
 		rxq->gdma_rq.tail += desc->wqe_size_in_bu;
 
-		/* Consume this request and post another request */
-		ret = mana_alloc_and_post_rx_wqe(rxq);
-		if (ret) {
-			DP_LOG(ERR, "failed to post rx wqe ret=%d", ret);
-			break;
-		}
-
-		wqe_posted++;
+		/* Record the number of the RX WQE we need to post to replenish
+		 * consumed RX requests
+		 */
+		wqe_consumed++;
 		if (pkt_received == pkts_n)
 			break;
 
 #ifdef RTE_ARCH_32
+		/* Always post WQE as soon as it's consumed for short DB */
+		ret = mana_alloc_and_post_rx_wqes(rxq, wqe_consumed);
+		if (ret) {
+			DRV_LOG(ERR, "failed to post %d WQEs, ret %d",
+				wqe_consumed, ret);
+			return pkt_received;
+		}
+		wqe_consumed = 0;
+
 		/* Ring short doorbell if approaching the wqe increment
 		 * limit.
 		 */
@@ -569,8 +589,12 @@ mana_rx_burst(void *dpdk_rxq, struct rte_mbuf **pkts, uint16_t pkts_n)
 		goto repoll;
 	}
 
-	if (wqe_posted)
-		mana_rq_ring_doorbell(rxq);
+	if (wqe_consumed) {
+		ret = mana_alloc_and_post_rx_wqes(rxq, wqe_consumed);
+		if (ret)
+			DRV_LOG(ERR, "failed to post %d WQEs, ret %d",
+				wqe_consumed, ret);
+	}
 
 	return pkt_received;
 }
-- 
2.17.1