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

[Petri Savolainen]

Add short warm up round and measure over a longer period of
time (250ms vs 100ms).

Signed-off-by: Petri Savolainen <petri.savolai...@linaro.org>
---
 platform/linux-generic/arch/x86/odp_cpu_arch.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

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);
 }
-- 
2.11.0