diff -r a7642acd9caf xen/arch/x86/time.c
--- a/xen/arch/x86/time.c	Fri Jul 25 10:06:53 2008 +0100
+++ b/xen/arch/x86/time.c	Sun Jul 27 06:31:19 2008 -0600
@@ -35,7 +35,8 @@ static char opt_clocksource[10];
 static char opt_clocksource[10];
 string_param("clocksource", opt_clocksource);
 
-#define EPOCH MILLISECS(1000)
+#define EPOCH (1ULL<<30)
+#define NEXT_ROUNDED_EPOCH(now)  (((now) + (EPOCH+(EPOCH/2))) & ~(EPOCH-1))
 
 unsigned long cpu_khz;  /* CPU clock frequency in kHz. */
 DEFINE_SPINLOCK(rtc_lock);
@@ -1021,7 +1022,7 @@ static void local_time_calibration(void 
     update_vcpu_system_time(current);
 
  out:
-    set_timer(&t->calibration_timer, NOW() + EPOCH);
+    set_timer(&t->calibration_timer, NEXT_ROUNDED_EPOCH(curr_local_stime));
 
     if ( smp_processor_id() == 0 )
         platform_time_calibration();
@@ -1050,7 +1051,7 @@ void init_percpu_time(void)
  out:
     init_timer(&t->calibration_timer, local_time_calibration,
                NULL, smp_processor_id());
-    set_timer(&t->calibration_timer, NOW() + EPOCH);
+    set_timer(&t->calibration_timer, NEXT_ROUNDED_EPOCH(NOW()));
 }
 
 /* Late init function (after all CPUs are booted). */