[PATCH v3 1/2] net/memif: add a Rx fast path

[Joyce Kong <joyce.kong@arm.com>]

For memif non-zero-copy mode, there is a branch to compare
the mbuf and memif buffer size during memory copying. Mbuf
and memif buffer size is defined at compile time. If memif
buf size <= mbuf size, add a fast Rx memory copy path by
removing this branch and mbuf bulk alloc.

The removal of the branch and bulk alloc lead to considerable
performance uplift.

Test with 1p1q on N1SDP AArch64 server,
--------------------------------------------
  buf size  | memif <= mbuf | memif > mbuf |
--------------------------------------------
non-zc gain |     26.85%    |    -0.37%    |
--------------------------------------------
   zc gain  |      8.57%    |     3.04%    |
--------------------------------------------

Test with 1p1q on Cascade Lake Xeon X86 server,
--------------------------------------------
  buf size  | memif <= mbuf | memif > mbuf |
--------------------------------------------
non-zc gain |     17.54%    |    -0.42%    |
--------------------------------------------
   zc gain  |     10.67%    |     0.26%    |
--------------------------------------------

Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
---
 drivers/net/memif/rte_eth_memif.c | 137 +++++++++++++++++++++---------
 1 file changed, 96 insertions(+), 41 deletions(-)

diff --git a/drivers/net/memif/rte_eth_memif.c b/drivers/net/memif/rte_eth_memif.c
index dd951b8296..2ea2a8e266 100644
--- a/drivers/net/memif/rte_eth_memif.c
+++ b/drivers/net/memif/rte_eth_memif.c
@@ -342,66 +342,122 @@ eth_memif_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 		goto refill;
 	n_slots = last_slot - cur_slot;
 
-	while (n_slots && n_rx_pkts < nb_pkts) {
-		mbuf_head = rte_pktmbuf_alloc(mq->mempool);
-		if (unlikely(mbuf_head == NULL))
-			goto no_free_bufs;
-		mbuf = mbuf_head;
-		mbuf->port = mq->in_port;
-		dst_off = 0;
+	if (likely(mbuf_size >= pmd->cfg.pkt_buffer_size)) {
+		struct rte_mbuf *mbufs[nb_pkts];
+		ret = rte_pktmbuf_alloc_bulk(mq->mempool, mbufs, nb_pkts);
+			if (unlikely(ret < 0))
+				goto no_free_bufs;
+
+		while (n_slots && n_rx_pkts < nb_pkts) {
+			mbuf_head = mbufs[n_rx_pkts];
+			mbuf = mbuf_head;
+
+next_slot1:
+			mbuf->port = mq->in_port;
+			s0 = cur_slot & mask;
+			d0 = &ring->desc[s0];
 
-next_slot:
-		s0 = cur_slot & mask;
-		d0 = &ring->desc[s0];
+			cp_len = d0->length;
 
-		src_len = d0->length;
-		src_off = 0;
+			rte_pktmbuf_data_len(mbuf) = cp_len;
+			rte_pktmbuf_pkt_len(mbuf) = cp_len;
+			if (mbuf != mbuf_head)
+				rte_pktmbuf_pkt_len(mbuf_head) += cp_len;
 
-		do {
-			dst_len = mbuf_size - dst_off;
-			if (dst_len == 0) {
-				dst_off = 0;
-				dst_len = mbuf_size;
+			rte_memcpy(rte_pktmbuf_mtod(mbuf, void *),
+				(uint8_t *)memif_get_buffer(proc_private, d0), cp_len);
 
-				/* store pointer to tail */
+			cur_slot++;
+			n_slots--;
+
+			if (d0->flags & MEMIF_DESC_FLAG_NEXT) {
 				mbuf_tail = mbuf;
 				mbuf = rte_pktmbuf_alloc(mq->mempool);
-				if (unlikely(mbuf == NULL))
+				if (unlikely(mbuf == NULL)) {
+					rte_pktmbuf_free_bulk(mbufs + n_rx_pkts,
+							nb_pkts - n_rx_pkts);
 					goto no_free_bufs;
-				mbuf->port = mq->in_port;
+				}
 				ret = memif_pktmbuf_chain(mbuf_head, mbuf_tail, mbuf);
 				if (unlikely(ret < 0)) {
 					MIF_LOG(ERR, "number-of-segments-overflow");
 					rte_pktmbuf_free(mbuf);
+					rte_pktmbuf_free_bulk(mbufs + n_rx_pkts,
+							nb_pkts - n_rx_pkts);
 					goto no_free_bufs;
 				}
+				goto next_slot1;
 			}
-			cp_len = RTE_MIN(dst_len, src_len);
 
-			rte_pktmbuf_data_len(mbuf) += cp_len;
-			rte_pktmbuf_pkt_len(mbuf) = rte_pktmbuf_data_len(mbuf);
-			if (mbuf != mbuf_head)
-				rte_pktmbuf_pkt_len(mbuf_head) += cp_len;
+			mq->n_bytes += rte_pktmbuf_pkt_len(mbuf_head);
+			*bufs++ = mbuf_head;
+			n_rx_pkts++;
+		}
 
-			rte_memcpy(rte_pktmbuf_mtod_offset(mbuf, void *,
-							   dst_off),
-				(uint8_t *)memif_get_buffer(proc_private, d0) +
-				src_off, cp_len);
+		if (n_rx_pkts < nb_pkts)
+			rte_pktmbuf_free_bulk(mbufs + n_rx_pkts, nb_pkts - n_rx_pkts);
+	} else {
+		while (n_slots && n_rx_pkts < nb_pkts) {
+			mbuf_head = rte_pktmbuf_alloc(mq->mempool);
+			if (unlikely(mbuf_head == NULL))
+				goto no_free_bufs;
+			mbuf = mbuf_head;
+			mbuf->port = mq->in_port;
+
+next_slot2:
+			s0 = cur_slot & mask;
+			d0 = &ring->desc[s0];
 
-			src_off += cp_len;
-			dst_off += cp_len;
-			src_len -= cp_len;
-		} while (src_len);
+			src_len = d0->length;
+			dst_off = 0;
+			src_off = 0;
 
-		cur_slot++;
-		n_slots--;
+			do {
+				dst_len = mbuf_size - dst_off;
+				if (dst_len == 0) {
+					dst_off = 0;
+					dst_len = mbuf_size;
+
+					/* store pointer to tail */
+					mbuf_tail = mbuf;
+					mbuf = rte_pktmbuf_alloc(mq->mempool);
+					if (unlikely(mbuf == NULL))
+						goto no_free_bufs;
+					mbuf->port = mq->in_port;
+					ret = memif_pktmbuf_chain(mbuf_head, mbuf_tail, mbuf);
+					if (unlikely(ret < 0)) {
+						MIF_LOG(ERR, "number-of-segments-overflow");
+						rte_pktmbuf_free(mbuf);
+						goto no_free_bufs;
+					}
+				}
+				cp_len = RTE_MIN(dst_len, src_len);
 
-		if (d0->flags & MEMIF_DESC_FLAG_NEXT)
-			goto next_slot;
+				rte_pktmbuf_data_len(mbuf) += cp_len;
+				rte_pktmbuf_pkt_len(mbuf) = rte_pktmbuf_data_len(mbuf);
+				if (mbuf != mbuf_head)
+					rte_pktmbuf_pkt_len(mbuf_head) += cp_len;
 
-		mq->n_bytes += rte_pktmbuf_pkt_len(mbuf_head);
-		*bufs++ = mbuf_head;
-		n_rx_pkts++;
+				rte_memcpy(rte_pktmbuf_mtod_offset(mbuf, void *,
+								   dst_off),
+					(uint8_t *)memif_get_buffer(proc_private, d0) +
+					src_off, cp_len);
+
+				src_off += cp_len;
+				dst_off += cp_len;
+				src_len -= cp_len;
+			} while (src_len);
+
+			cur_slot++;
+			n_slots--;
+
+			if (d0->flags & MEMIF_DESC_FLAG_NEXT)
+				goto next_slot2;
+
+			mq->n_bytes += rte_pktmbuf_pkt_len(mbuf_head);
+			*bufs++ = mbuf_head;
+			n_rx_pkts++;
+		}
 	}
 
 no_free_bufs:
@@ -694,7 +750,6 @@ eth_memif_tx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
 	return n_tx_pkts;
 }
 
-
 static int
 memif_tx_one_zc(struct pmd_process_private *proc_private, struct memif_queue *mq,
 		memif_ring_t *ring, struct rte_mbuf *mbuf, const uint16_t mask,
-- 
2.25.1