[PATCH] disable lost tick compensation before TSCs are synced

Avoid lost tick compensation early in boot before the TSCs are synchronized. Currently timekeeping is enabled before the TSCs are synchronized, thus when the TSCs are synched (reset to zero), it appears that a number of lost ticks have occurred. This can cause premature expiry of timers and in extreme cases can cause the soft lockup detection to fire. This resolves issues reported by Andy Whitcroft as well as bug #5366 reported by Tim Mann. Signed-off-by: John Stultz <[email protected]> Acked-by: Andy Whitcroft <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
benxu · Feb 1, 2006 · bfaa1de · bfaa1de
1 parent 2f7016d
commit bfaa1de
Showing 1 changed file with 12 additions and 2 deletions.
diff --git a/arch/i386/kernel/timers/timer_tsc.c b/arch/i386/kernel/timers/timer_tsc.c
@@ -45,6 +45,15 @@ static unsigned long last_tsc_high; /* msb 32 bits of Time Stamp Counter */
 static unsigned long long monotonic_base;
 static seqlock_t monotonic_lock = SEQLOCK_UNLOCKED;
 
+/* Avoid compensating for lost ticks before TSCs are synched */
+static int detect_lost_ticks;
+static int __init start_lost_tick_compensation(void)
+{
+	detect_lost_ticks = 1;
+	return 0;
+}
+late_initcall(start_lost_tick_compensation);
+
 /* convert from cycles(64bits) => nanoseconds (64bits)
  *  basic equation:
  *		ns = cycles / (freq / ns_per_sec)
@@ -196,7 +205,8 @@ static void mark_offset_tsc_hpet(void)
 
 	/* lost tick compensation */
 	offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
-	if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))) {
+	if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))
+					&& detect_lost_ticks) {
 		int lost_ticks = (offset - hpet_last) / hpet_tick;
 		jiffies_64 += lost_ticks;
 	}
@@ -421,7 +431,7 @@ static void mark_offset_tsc(void)
 	delta += delay_at_last_interrupt;
 	lost = delta/(1000000/HZ);
 	delay = delta%(1000000/HZ);
-	if (lost >= 2) {
+	if (lost >= 2 && detect_lost_ticks) {
 		jiffies_64 += lost-1;
 
 		/* sanity check to ensure we're not always losing ticks */