#include <vppinfra/time.h>
#include <vppinfra/format.h>
#include <vppinfra/cpu.h>
+#include <math.h>
#ifdef CLIB_UNIX
static f64
estimate_clock_frequency (f64 sample_time)
{
- /* Round to nearest 100KHz. */
- const f64 round_to_units = 100e5;
-
f64 time_now, time_start, time_limit, freq;
- u64 ifreq, t[2];
+ u64 t[2];
time_start = time_now = unix_time_now ();
time_limit = time_now + sample_time;
t[1] = clib_cpu_time_now ();
freq = (t[1] - t[0]) / (time_now - time_start);
- ifreq = flt_round_nearest (freq / round_to_units);
- freq = ifreq * round_to_units;
return freq;
}
}
#endif
+ /* If we have an invariant TSC, use it to estimate the clock frequency */
if (clib_cpu_supports_invariant_tsc ())
return estimate_clock_frequency (1e-3);
- /* First try /sys version. */
+ /* Next, try /sys version. */
cpu_freq = clock_frequency_from_sys_filesystem ();
if (cpu_freq != 0)
return cpu_freq;
c->seconds_per_clock = 1 / c->clocks_per_second;
c->log2_clocks_per_second = min_log2_u64 ((u64) c->clocks_per_second);
- /* Initially verify frequency every sec */
- c->log2_clocks_per_frequency_verify = c->log2_clocks_per_second;
+ /* Verify frequency every 16 sec */
+ c->log2_clocks_per_frequency_verify = c->log2_clocks_per_second + 4;
c->last_verify_reference_time = unix_time_now ();
+ c->init_reference_time = c->last_verify_reference_time;
c->last_cpu_time = clib_cpu_time_now ();
c->init_cpu_time = c->last_verify_cpu_time = c->last_cpu_time;
+ c->total_cpu_time = 0ULL;
+
+ /*
+ * Use exponential smoothing, with a half-life of 1 minute
+ * reported_rate(t) = reported_rate(t-1) * K + rate(t)*(1-K)
+ * where K = e**(-1.0/3.75);
+ * 15 samples in 4 minutes
+ * 7.5 samples in 2 minutes,
+ * 3.75 samples in 1 minute, etc.
+ */
+ c->damping_constant = exp (-1.0 / 3.75);
}
void
clib_time_verify_frequency (clib_time_t * c)
{
- f64 now_reference = unix_time_now ();
- f64 dtr = now_reference - c->last_verify_reference_time;
- f64 dtr_max;
- u64 dtc = c->last_cpu_time - c->last_verify_cpu_time;
+ f64 now_reference, delta_reference, delta_reference_max;
+ u64 delta_clock;
f64 new_clocks_per_second, delta;
- f64 save_total_cpu_time_in_seconds;
+
+ /* Ask the kernel and the CPU what time it is... */
+ now_reference = unix_time_now ();
+ c->last_cpu_time = clib_cpu_time_now ();
+
+ /* Calculate a new clock rate sample */
+ delta_reference = now_reference - c->last_verify_reference_time;
+ delta_clock = c->last_cpu_time - c->last_verify_cpu_time;
c->last_verify_cpu_time = c->last_cpu_time;
c->last_verify_reference_time = now_reference;
* or off by a factor of two - or 8 seconds - whichever is larger?
* Someone reset the clock behind our back.
*/
- dtr_max = (f64) (2ULL << c->log2_clocks_per_frequency_verify) /
+ delta_reference_max = (f64) (2ULL << c->log2_clocks_per_frequency_verify) /
(f64) (1ULL << c->log2_clocks_per_second);
- dtr_max = dtr_max > 8.0 ? dtr_max : 8.0;
-
- if (dtr <= 0.0 || dtr > dtr_max)
- {
- c->log2_clocks_per_frequency_verify = c->log2_clocks_per_second;
- return;
- }
+ delta_reference_max = delta_reference_max > 8.0 ? delta_reference_max : 8.0;
- 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);
- }
+ /* Ignore this sample */
+ if (delta_reference <= 0.0 || delta_reference > delta_reference_max)
+ return;
/*
* Reject large frequency changes, another consequence of
* system clock changes particularly with old kernels.
*/
- new_clocks_per_second =
- flt_round_nearest ((f64) dtc / (dtr * c->round_to_units))
- * c->round_to_units;
+ new_clocks_per_second = ((f64) delta_clock) / delta_reference;
/* Compute abs(rate change) */
delta = new_clocks_per_second - c->clocks_per_second;
if (delta < 0.0)
delta = -delta;
- /* If rate change > 1%, reject it and try again */
+ /* If rate change > 1%, reject this sample */
if (PREDICT_FALSE ((delta / c->clocks_per_second) > .01))
{
clib_warning ("Rejecting large frequency change of %.2f%%",
(delta / c->clocks_per_second) * 100.0);
- c->log2_clocks_per_frequency_verify = c->log2_clocks_per_second;
return;
}
- /* Save total cpu time in seconds */
- save_total_cpu_time_in_seconds = c->total_cpu_time * c->seconds_per_clock;
-
- /* Recalculate clock rate */
- c->clocks_per_second = new_clocks_per_second;
- c->seconds_per_clock = 1 / c->clocks_per_second;
+ /* Add sample to the exponentially-smoothed rate */
+ c->clocks_per_second = c->clocks_per_second * c->damping_constant +
+ (1.0 - c->damping_constant) * new_clocks_per_second;
+ c->seconds_per_clock = 1.0 / c->clocks_per_second;
/*
- * Restore total cpu time in seconds. Otherwise, if c->clocks_per_second
- * has decreased, time may appear to flow backwards.
+ * Recalculate total_cpu_time based on the kernel timebase, and
+ * the calculated clock rate
*/
- c->total_cpu_time = save_total_cpu_time_in_seconds * c->clocks_per_second;
+ c->total_cpu_time =
+ (now_reference - c->init_reference_time) * c->clocks_per_second;
+}
+
+
+u8 *
+format_clib_time (u8 * s, va_list * args)
+{
+ clib_time_t *c = va_arg (*args, clib_time_t *);
+ int verbose = va_arg (*args, int);
+ f64 now, reftime, delta_reftime_in_seconds, error;
+
+ /* Compute vpp elapsed time from the CPU clock */
+ reftime = unix_time_now ();
+ now = clib_time_now (c);
+
+ s = format (s, "Time now %.6f", now);
+ if (verbose == 0)
+ return s;
+
+ /* And also from the kernel */
+ delta_reftime_in_seconds = reftime - c->init_reference_time;
+
+ error = now - delta_reftime_in_seconds;
- /* Double time between verifies; max at 64 secs ~ 1 minute. */
- if (c->log2_clocks_per_frequency_verify < c->log2_clocks_per_second + 6)
- c->log2_clocks_per_frequency_verify += 1;
+ s = format (s, ", reftime %.6f, error %.6f, clocks/sec %.6f",
+ delta_reftime_in_seconds, error, c->clocks_per_second);
+ return (s);
}
/*
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