[Title] Enhance the system clock to approximate to realtime smoothly

[Type] Feature/BugFix/Enahncement
[Module] kernel/time
[Priority]
[CQ#]
[Redmine#]
[Problem]
[Cause]
[Solution] Interpolate the time slip between host and kernel
[TestCase]

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index a3b3fe91af984a4c660a267acd06652dc9d215bd..b973c7d36eb572b2865f2446b37df5f97510df4c 100644 (file)
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -57,7 +57,8 @@ int tick_is_oneshot_available(void)
 /*
  * Periodic tick
  */
-static void tick_periodic(int cpu)
+#define UNDER_HYPERVISOR
+void tick_periodic(int cpu)
 {
        if (tick_do_timer_cpu == cpu) {
                write_seqlock(&xtime_lock);
@@ -65,28 +66,43 @@ static void tick_periodic(int cpu)
                /* Keep track of the next tick event */
                tick_next_period = ktime_add(tick_next_period, tick_period);
 
-               if (0 == (jiffies & 0x7)) {
-                       static __kernel_time_t rt;
-                       static unsigned long rt_jiffies = INITIAL_JIFFIES;
-
-                       unsigned long tick = 1;
-
-                       struct timespec ts;
-                       read_persistent_clock(&ts);
+               #ifdef UNDER_HYPERVISOR
+               {       /* Compensate slow timer tick under hypervisor */
+                       static __kernel_time_t rt_sec;
+                       static unsigned long rt_jiffies_sec = HZ;
+                       static unsigned long rt_ticks_sec = HZ;
+                       static unsigned long rt_tick = 0;
+                       static unsigned long rt_current = 0;
+                       static unsigned long rt_count = 1;
+
+                       unsigned long tick = rt_jiffies_sec * ++rt_tick / rt_ticks_sec - rt_current;
+                       rt_current += tick;
+                       do_timer(tick);
 
-                       if (rt != ts.tv_sec) {
-                               rt = ts.tv_sec;
-                               rt_jiffies += HZ;
-                               if (rt_jiffies>jiffies) {
-                                       tick=rt_jiffies-jiffies;
-                                       if (tick > HZ)
-                                               tick = 1;
+                       if( 0 == --rt_count ) {
+                               static int first = 2;
+
+                               struct timespec ts;
+                               read_persistent_clock(&ts);
+
+                               if (rt_sec != ts.tv_sec) {
+                                       if (!first) {
+                                               rt_jiffies_sec = HZ + rt_jiffies_sec - rt_current;
+                                               rt_ticks_sec = rt_tick;
+                                       } else {
+                                               first--;
+                                       }
+                                       rt_sec = ts.tv_sec;
+                                       rt_tick = rt_current = 0;
                                }
+
+                               rt_count = (!first && rt_ticks_sec > rt_tick + 3) ? (rt_ticks_sec - rt_tick) >> 2 : 1;
                        }
-                       do_timer(tick);
                }
-               else
+               #else
                do_timer(1);
+               #endif /* End of UNDER_HYPERVISOR */
+
                write_sequnlock(&xtime_lock);
        }