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[API-NEXT,v3,10/11] linux-gen: time: improve x86 TSC freq measurement accuracy

Message ID 20170428120958.17526-11-petri.savolainen@linaro.org
State New
Headers show
Series Use HW time counter | expand

Commit Message

Petri Savolainen April 28, 2017, 12:09 p.m. UTC 
Add short warm up round and measure over a longer period of
time (250ms vs 100ms).

Signed-off-by: Petri Savolainen <petri.savolainen@linaro.org>

---
 platform/linux-generic/arch/x86/odp_cpu_arch.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

-- 
2.11.0
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Patch

diff --git a/platform/linux-generic/arch/x86/odp_cpu_arch.c b/platform/linux-generic/arch/x86/odp_cpu_arch.c
index 9ba601a3..b1da428b 100644
--- a/platform/linux-generic/arch/x86/odp_cpu_arch.c
+++ b/platform/linux-generic/arch/x86/odp_cpu_arch.c
@@ -54,11 +54,16 @@  uint64_t cpu_global_time_freq(void)
 	uint64_t t1, t2, ts_nsec, cycles, hz;
 	int i;
 	uint64_t avg = 0;
-	int rounds = 4;
+	int rounds = 3;
+	int warm_up = 1;
 
 	for (i = 0; i < rounds; i++) {
-		sleep.tv_sec  = 0;
-		sleep.tv_nsec = SEC_IN_NS / 10;
+		sleep.tv_sec = 0;
+
+		if (warm_up)
+			sleep.tv_nsec = SEC_IN_NS / 1000;
+		else
+			sleep.tv_nsec = SEC_IN_NS / 4;
 
 		if (clock_gettime(CLOCK_MONOTONIC_RAW, &ts1)) {
 			ODP_DBG("clock_gettime failed\n");
@@ -85,8 +90,12 @@  uint64_t cpu_global_time_freq(void)
 		cycles = t2 - t1;
 
 		hz = (cycles * SEC_IN_NS) / ts_nsec;
-		avg += hz;
+
+		if (warm_up)
+			warm_up = 0;
+		else
+			avg += hz;
 	}
 
-	return avg / rounds;
+	return avg / (rounds - 1);
 }