[dpdk-dev] [PATCH 3/4] examples/l3fwd: eliminate unnecessary reloads in loop

[Ruifeng Wang]

Number of rx queue and number of rx port in lcore config are constants
during the period of l3 forward application running. But compiler has
no this information.

Copied values from lcore config to local variables and used the local
variables for iteration. Compiler can see that the local variables are
not changed, so qconf reloads at each iteration can be eliminated.

The change showed 1.8% performance uplift in single core, single port,
single queue test on N1SDP platform with MLX5 NIC.

Signed-off-by: Ruifeng Wang <ruifeng.wang at arm.com>
---
 examples/l3fwd/l3fwd_lpm.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/examples/l3fwd/l3fwd_lpm.c b/examples/l3fwd/l3fwd_lpm.c
index 3dcf1fef1..d338590b9 100644
--- a/examples/l3fwd/l3fwd_lpm.c
+++ b/examples/l3fwd/l3fwd_lpm.c
@@ -190,14 +190,16 @@ lpm_main_loop(__rte_unused void *dummy)
 	lcore_id = rte_lcore_id();
 	qconf = &lcore_conf[lcore_id];
 
-	if (qconf->n_rx_queue == 0) {
+	uint16_t n_rx_q = qconf->n_rx_queue;
+	uint16_t n_tx_p = qconf->n_tx_port;
+	if (n_rx_q == 0) {
 		RTE_LOG(INFO, L3FWD, "lcore %u has nothing to do\n", lcore_id);
 		return 0;
 	}
 
 	RTE_LOG(INFO, L3FWD, "entering main loop on lcore %u\n", lcore_id);
 
-	for (i = 0; i < qconf->n_rx_queue; i++) {
+	for (i = 0; i < n_rx_q; i++) {
 
 		portid = qconf->rx_queue_list[i].port_id;
 		queueid = qconf->rx_queue_list[i].queue_id;
@@ -216,7 +218,7 @@ lpm_main_loop(__rte_unused void *dummy)
 		diff_tsc = cur_tsc - prev_tsc;
 		if (unlikely(diff_tsc > drain_tsc)) {
 
-			for (i = 0; i < qconf->n_tx_port; ++i) {
+			for (i = 0; i < n_tx_p; ++i) {
 				portid = qconf->tx_port_id[i];
 				if (qconf->tx_mbufs[portid].len == 0)
 					continue;
@@ -232,7 +234,7 @@ lpm_main_loop(__rte_unused void *dummy)
 		/*
 		 * Read packet from RX queues
 		 */
-		for (i = 0; i < qconf->n_rx_queue; ++i) {
+		for (i = 0; i < n_rx_q; ++i) {
 			portid = qconf->rx_queue_list[i].port_id;
 			queueid = qconf->rx_queue_list[i].queue_id;
 			nb_rx = rte_eth_rx_burst(portid, queueid, pkts_burst,
-- 
2.25.1