[dpdk-dev] [PATCH] examples/timer: fix incorrect time interval

["Min Hu (Connor)" <humin29@huawei.com>]

From: Chengchang Tang <tangchengchang@huawei.com>

Timer sample example assumes that the frequency of the timer is about
2Ghz to control the period of calling rte_timer_manage(). But this
assumption is easy to fail. For example. the frequency of tsc on ARM64
is much less than 2Ghz.

This patch uses the frequency of the current timer to calculate the
correct time interval to ensure consistent result on all platforms.

In addition, the rte_rdtsc() is replaced with the more recommended
rte_get_timer_cycles function in this patch.

Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org

Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Signed-off-by: Min Hu (Connor) <humin29@huawei.com>
---
 examples/timer/main.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/examples/timer/main.c b/examples/timer/main.c
index 5a57e48..05f4a9f 100644
--- a/examples/timer/main.c
+++ b/examples/timer/main.c
@@ -18,8 +18,7 @@
 #include <rte_timer.h>
 #include <rte_debug.h>
 
-#define TIMER_RESOLUTION_CYCLES 20000000ULL /* around 10ms at 2 Ghz */
-
+static uint64_t timer_resolution_cycles;
 static struct rte_timer timer0;
 static struct rte_timer timer1;
 
@@ -66,15 +65,16 @@ lcore_mainloop(__rte_unused void *arg)
 
 	while (1) {
 		/*
-		 * Call the timer handler on each core: as we don't
-		 * need a very precise timer, so only call
-		 * rte_timer_manage() every ~10ms (at 2Ghz). In a real
-		 * application, this will enhance performances as
-		 * reading the HPET timer is not efficient.
+		 * Call the timer handler on each core: as we don't need a
+		 * very precise timer, so only call rte_timer_manage()
+		 * every ~10ms. since rte_eal_hpet_init() has not been
+		 * called, the rte_rdtsc() will be used at runtime.
+		 * In a real application, this will enhance performances
+		 * as reading the HPET timer is not efficient.
 		 */
-		cur_tsc = rte_rdtsc();
+		cur_tsc = rte_get_timer_cycles();
 		diff_tsc = cur_tsc - prev_tsc;
-		if (diff_tsc > TIMER_RESOLUTION_CYCLES) {
+		if (diff_tsc > timer_resolution_cycles) {
 			rte_timer_manage();
 			prev_tsc = cur_tsc;
 		}
@@ -100,8 +100,10 @@ main(int argc, char **argv)
 	rte_timer_init(&timer0);
 	rte_timer_init(&timer1);
 
-	/* load timer0, every second, on main lcore, reloaded automatically */
 	hz = rte_get_timer_hz();
+	timer_resolution_cycles = hz * 10 / 1000; /* around 10ms */
+
+	/* load timer0, every second, on main lcore, reloaded automatically */
 	lcore_id = rte_lcore_id();
 	rte_timer_reset(&timer0, hz, PERIODICAL, lcore_id, timer0_cb, NULL);
 
-- 
2.7.4