Improve NTP / kernel time change event handling

[vpp.git] / src / vppinfra / time.c

diff --git a/src/vppinfra/time.c b/src/vppinfra/time.c
index 770ed8b..d647e67 100644 (file)
--- a/src/vppinfra/time.c
+++ b/src/vppinfra/time.c
@@ -142,17 +142,20 @@ done:
 f64
 os_cpu_clock_frequency (void)
 {
+#if defined (__aarch64__)
+  /* The system counter increments at a fixed frequency. It is distributed
+   * to each core which has registers for reading the current counter value
+   * as well as the clock frequency. The system counter is not clocked at
+   * the same frequency as the core. */
+  u64 hz;
+  asm volatile ("mrs %0, cntfrq_el0":"=r" (hz));
+  return (f64) hz;
+#endif
   f64 cpu_freq;
 
   if (clib_cpu_supports_invariant_tsc ())
     return estimate_clock_frequency (1e-3);
 
-#if defined (__aarch64__)
-  u64 tsc;
-  asm volatile ("mrs %0, CNTFRQ_EL0":"=r" (tsc));
-  return (f64) tsc;
-#endif
-
   /* First try /sys version. */
   cpu_freq = clock_frequency_from_sys_filesystem ();
   if (cpu_freq != 0)
@@ -194,6 +197,7 @@ clib_time_verify_frequency (clib_time_t * c)
   f64 dtr = now_reference - c->last_verify_reference_time;
   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;
@@ -214,6 +218,25 @@ clib_time_verify_frequency (clib_time_t * c)
       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 * round_units)) * round_units;
+
+  delta = new_clocks_per_second - c->clocks_per_second;
+  if (delta < 0.0)
+    delta = -delta;
+
+  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;
+    }
+
   c->clocks_per_second =
     flt_round_nearest ((f64) dtc / (dtr * round_units)) * round_units;
   c->seconds_per_clock = 1 / c->clocks_per_second;