timers: Fix get_next_timer_interrupt() computation

[cascardo/linux.git] / kernel / time / timer.c

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 8f29abe..32bf6f7 100644 (file)
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1496,6 +1496,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
        struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
        u64 expires = KTIME_MAX;
        unsigned long nextevt;
+       bool is_max_delta;
 
        /*
         * Pretend that there is no timer pending if the cpu is offline.
@@ -1506,6 +1507,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 
        spin_lock(&base->lock);
        nextevt = __next_timer_interrupt(base);
+       is_max_delta = (nextevt == base->clk + NEXT_TIMER_MAX_DELTA);
        base->next_expiry = nextevt;
        /*
         * We have a fresh next event. Check whether we can forward the base:
@@ -1519,7 +1521,8 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
                expires = basem;
                base->is_idle = false;
        } else {
-               expires = basem + (nextevt - basej) * TICK_NSEC;
+               if (!is_max_delta)
+                       expires = basem + (nextevt - basej) * TICK_NSEC;
                /*
                 * If we expect to sleep more than a tick, mark the base idle:
                 */
@@ -1804,7 +1807,7 @@ static void migrate_timer_list(struct timer_base *new_base, struct hlist_head *h
        }
 }
 
-static void migrate_timers(int cpu)
+int timers_dead_cpu(unsigned int cpu)
 {
        struct timer_base *old_base;
        struct timer_base *new_base;
@@ -1831,29 +1834,9 @@ static void migrate_timers(int cpu)
                spin_unlock_irq(&new_base->lock);
                put_cpu_ptr(&timer_bases);
        }
+       return 0;
 }
 
-static int timer_cpu_notify(struct notifier_block *self,
-                               unsigned long action, void *hcpu)
-{
-       switch (action) {
-       case CPU_DEAD:
-       case CPU_DEAD_FROZEN:
-               migrate_timers((long)hcpu);
-               break;
-       default:
-               break;
-       }
-
-       return NOTIFY_OK;
-}
-
-static inline void timer_register_cpu_notifier(void)
-{
-       cpu_notifier(timer_cpu_notify, 0);
-}
-#else
-static inline void timer_register_cpu_notifier(void) { }
 #endif /* CONFIG_HOTPLUG_CPU */
 
 static void __init init_timer_cpu(int cpu)
@@ -1881,7 +1864,6 @@ void __init init_timers(void)
 {
        init_timer_cpus();
        init_timer_stats();
-       timer_register_cpu_notifier();
        open_softirq(TIMER_SOFTIRQ, run_timer_softirq);
 }
 
@@ -1925,9 +1907,15 @@ static void __sched do_usleep_range(unsigned long min, unsigned long max)
 }
 
 /**
- * usleep_range - Drop in replacement for udelay where wakeup is flexible
+ * usleep_range - Sleep for an approximate time
  * @min: Minimum time in usecs to sleep
  * @max: Maximum time in usecs to sleep
+ *
+ * In non-atomic context where the exact wakeup time is flexible, use
+ * usleep_range() instead of udelay().  The sleep improves responsiveness
+ * by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces
+ * power usage by allowing hrtimers to take advantage of an already-
+ * scheduled interrupt instead of scheduling a new one just for this sleep.
  */
 void __sched usleep_range(unsigned long min, unsigned long max)
 {