diff options
Diffstat (limited to 'src/vppinfra')
| -rw-r--r-- | src/vppinfra/time.c | 120 | ||||
| -rw-r--r-- | src/vppinfra/time.h | 10 |
2 files changed, 76 insertions, 54 deletions
diff --git a/src/vppinfra/time.c b/src/vppinfra/time.c index 35852a61cdf..3b3acfa3d1b 100644 --- a/src/vppinfra/time.c +++ b/src/vppinfra/time.c @@ -39,6 +39,7 @@ #include <vppinfra/time.h> #include <vppinfra/format.h> #include <vppinfra/cpu.h> +#include <math.h> #ifdef CLIB_UNIX @@ -51,11 +52,8 @@ 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; @@ -65,8 +63,6 @@ estimate_clock_frequency (f64 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; } @@ -185,10 +181,11 @@ os_cpu_clock_frequency (void) } #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; @@ -214,23 +211,40 @@ clib_time_init (clib_time_t * c) 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; @@ -240,68 +254,70 @@ clib_time_verify_frequency (clib_time_t * c) * 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); } /* diff --git a/src/vppinfra/time.h b/src/vppinfra/time.h index b2d749256d3..4d8997f0a9e 100644 --- a/src/vppinfra/time.h +++ b/src/vppinfra/time.h @@ -39,6 +39,7 @@ #define included_time_h #include <vppinfra/clib.h> +#include <vppinfra/format.h> typedef struct { @@ -56,10 +57,9 @@ 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; + f64 init_reference_time; u64 last_verify_cpu_time; @@ -67,8 +67,14 @@ typedef struct f64 last_verify_reference_time; u32 log2_clocks_per_second, log2_clocks_per_frequency_verify; + + /* Damping constant */ + f64 damping_constant; + } clib_time_t; +format_function_t format_clib_time; + /* Return CPU time stamp as 64bit number. */ #if defined(__x86_64__) || defined(i386) always_inline u64 |