[dpdk-dev] [memnic PATCH 6/7] pmd: add branch hint in recv/xmit

[Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>]

From: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>

To reduce instruction cache miss, add branch condition hints into
recv/xmit functions. This improves a bit performance.

We can see performance improvements with memnic-tester.
Using Xeon E5-2697 v2 @ 2.70GHz, 4 vCPU.
 size |  before  |  after
   64 | 5.54Mpps | 5.55Mpps
  128 | 5.46Mpps | 5.44Mpps
  256 | 5.21Mpps | 5.22Mpps
  512 | 4.50Mpps | 4.52Mpps
 1024 | 3.71Mpps | 3.73Mpps
 1280 | 3.21Mpps | 3.22Mpps
 1518 | 2.92Mpps | 2.93Mpps

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Reviewed-by: Hayato Momma <h-momma@ce.jp.nec.com>
---
 pmd/pmd_memnic.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/pmd/pmd_memnic.c b/pmd/pmd_memnic.c
index dbe5033..cc0ae25 100644
--- a/pmd/pmd_memnic.c
+++ b/pmd/pmd_memnic.c
@@ -289,26 +289,26 @@ static uint16_t memnic_recv_pkts(void *rx_queue,
 	int idx, next;
 	struct rte_eth_stats *st = &adapter->stats[rte_lcore_id()];
 
-	if (!adapter->nic->hdr.valid)
+	if (unlikely(!adapter->nic->hdr.valid))
 		return 0;
 
 	pkts = bytes = errs = 0;
 	idx = adapter->up_idx;
 	for (nr = 0; nr < nb_pkts; nr++) {
 		p = &data->packets[idx];
-		if (p->status != MEMNIC_PKT_ST_FILLED)
+		if (unlikely(p->status != MEMNIC_PKT_ST_FILLED))
 			break;
 		/* prefetch the next area */
 		next = idx;
-		if (++next >= MEMNIC_NR_PACKET)
+		if (unlikely(++next >= MEMNIC_NR_PACKET))
 			next = 0;
 		rte_prefetch0(&data->packets[next]);
-		if (p->len > framesz) {
+		if (unlikely(p->len > framesz)) {
 			errs++;
 			goto drop;
 		}
 		mb = rte_pktmbuf_alloc(adapter->mp);
-		if (!mb)
+		if (unlikely(!mb))
 			break;
 
 		rte_memcpy(rte_pktmbuf_mtod(mb, void *), p->data, p->len);
@@ -350,7 +350,7 @@ static uint16_t memnic_xmit_pkts(void *tx_queue,
 	uint64_t pkts, bytes, errs;
 	uint32_t framesz = adapter->framesz;
 
-	if (!adapter->nic->hdr.valid)
+	if (unlikely(!adapter->nic->hdr.valid))
 		return 0;
 
 	pkts = bytes = errs = 0;
@@ -360,7 +360,7 @@ static uint16_t memnic_xmit_pkts(void *tx_queue,
 		struct rte_mbuf *sg;
 		void *ptr;
 
-		if (pkt_len > framesz) {
+		if (unlikely(pkt_len > framesz)) {
 			errs++;
 			break;
 		}
@@ -379,7 +379,7 @@ retry:
 			goto retry;
 		}
 
-		if (idx != ACCESS_ONCE(adapter->down_idx)) {
+		if (unlikely(idx != ACCESS_ONCE(adapter->down_idx))) {
 			/*
 			 * host freed this and got false positive,
 			 * need to recover the status and retry.
@@ -388,7 +388,7 @@ retry:
 			goto retry;
 		}
 
-		if (++idx >= MEMNIC_NR_PACKET)
+		if (unlikely(++idx >= MEMNIC_NR_PACKET))
 			idx = 0;
 		adapter->down_idx = idx;
 
-- 
1.8.3.1