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authorDave Barach <dave@barachs.net>2018-11-07 17:40:19 -0500
committerDamjan Marion <dmarion@me.com>2018-11-08 19:05:52 +0000
commitba603ba706a5942b7a44178940cd9a0383b93292 (patch)
tree208843808efa3f4820b0d9bba481330e8650b5d1
parent5100aa9cb9e7acff35fa3bfde8aa95b5ace60344 (diff)
Calculate clock rounding constant
Compute the first power of ten which is greater than 0.1% of the clock rate. Save the result, and use it to round future results. The previous constant value - 1e7 - didn't work properly on aarch64. Change-Id: Ic021e3eb1b90c0d4a7d9f1b6425123f0c8b48b0b Signed-off-by: Dave Barach <dave@barachs.net>
-rw-r--r--src/vppinfra/time.c21
-rw-r--r--src/vppinfra/time.h2
2 files changed, 20 insertions, 3 deletions
diff --git a/src/vppinfra/time.c b/src/vppinfra/time.c
index afb1a867ec7..2bba1daba12 100644
--- a/src/vppinfra/time.c
+++ b/src/vppinfra/time.c
@@ -198,7 +198,6 @@ clib_time_verify_frequency (clib_time_t * c)
f64 dtr_max;
u64 dtc = c->last_cpu_time - c->last_verify_cpu_time;
f64 new_clocks_per_second, delta;
- f64 round_units = 100e5;
c->last_verify_cpu_time = c->last_cpu_time;
c->last_verify_reference_time = now_reference;
@@ -218,12 +217,27 @@ clib_time_verify_frequency (clib_time_t * c)
return;
}
+ if (PREDICT_FALSE (c->round_to_units == 0.0))
+ {
+ f64 next_pow10, est_round_to_units;
+ /*
+ * Compute the first power of ten which is greater than
+ * 0.1% of the new clock rate. Save the result, and use it
+ * to round future results, so we don't end up calculating
+ * silly-looking clock rates.
+ */
+ est_round_to_units = ((f64) dtc / dtr) * 0.001;
+ next_pow10 = ceil (log10 (est_round_to_units));
+ c->round_to_units = pow (10.0, next_pow10);
+ }
+
/*
* Reject large frequency changes, another consequence of
* system clock changes particularly with old kernels.
*/
new_clocks_per_second =
- flt_round_nearest ((f64) dtc / (dtr * round_units)) * round_units;
+ flt_round_nearest ((f64) dtc / (dtr * c->round_to_units))
+ * c->round_to_units;
delta = new_clocks_per_second - c->clocks_per_second;
if (delta < 0.0)
@@ -238,7 +252,8 @@ clib_time_verify_frequency (clib_time_t * c)
}
c->clocks_per_second =
- flt_round_nearest ((f64) dtc / (dtr * round_units)) * round_units;
+ flt_round_nearest ((f64) dtc / (dtr * c->round_to_units))
+ * c->round_to_units;
c->seconds_per_clock = 1 / c->clocks_per_second;
/* Double time between verifies; max at 64 secs ~ 1 minute. */
diff --git a/src/vppinfra/time.h b/src/vppinfra/time.h
index 64370d523bb..0327ce0fd05 100644
--- a/src/vppinfra/time.h
+++ b/src/vppinfra/time.h
@@ -56,6 +56,8 @@ typedef struct
from clock cycles into seconds. */
f64 seconds_per_clock;
+ f64 round_to_units;
+
/* Time stamp of call to clib_time_init call. */
u64 init_cpu_time;