diff -r 3157b54eb465 xen/arch/x86/hvm/hpet.c
--- a/xen/arch/x86/hvm/hpet.c	Thu Jan 04 16:34:19 2007 +0000
+++ b/xen/arch/x86/hvm/hpet.c	Wed Jan 10 16:50:52 2007 +0800
@@ -144,7 +144,7 @@ static void hpet_stop_timer(HPETState *h
 
 static void hpet_set_timer(HPETState *h, unsigned int tn)
 {
-    uint64_t tn_cmp, cur_tick;
+    uint64_t tn_cmp, cur_tick, scheduled, passed;
 
     ASSERT(tn < HPET_TIMER_NUM);
     
@@ -167,11 +167,25 @@ static void hpet_set_timer(HPETState *h,
         cur_tick = (uint32_t)cur_tick;
     }
 
-    if ( (int64_t)(tn_cmp - cur_tick) > 0 )
-        set_timer(&h->timers[tn], NOW() +
-                  hpet_tick_to_ns(h, tn_cmp-cur_tick));
-    else
-        set_timer(&h->timers[tn], NOW());
+    scheduled = tn_cmp - cur_tick;
+    if ( (int64_t)scheduled < 0 )
+    {
+        passed = cur_tick - tn_cmp;
+
+         /* the number of HPET tick that stands for
+          * 1/(2^10) second, namely, 0.9765625 millisecond */
+        #define  hpet_tiny_time_span  (h->tsc_freq >> 10)
+        if ( passed < hpet_tiny_time_span )
+             scheduled = 0;
+        else
+        {
+            if ( timer_is_32bit(h, tn) )
+                scheduled = (uint32_t)scheduled;
+            else
+                scheduled = (uint64_t)scheduled;
+        }
+    }
+    set_timer(&h->timers[tn], NOW() + hpet_tick_to_ns(h, scheduled));
 }
 
 static inline uint64_t hpet_fixup_reg(