1 files changed, 49 insertions, 2 deletions

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index c71bcd549241..b675a67c9ac3 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -43,6 +43,8 @@
 #include <linux/seq_file.h>
 #include <linux/err.h>
 #include <linux/debugobjects.h>
+#include <linux/sched.h>
+#include <linux/timer.h>
 
 #include <asm/uaccess.h>
 
@@ -198,8 +200,19 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
 {
         struct hrtimer_clock_base *new_base;
         struct hrtimer_cpu_base *new_cpu_base;
+        int cpu, preferred_cpu = -1;
+
+        cpu = smp_processor_id();
+#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
+        if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu)) {
+                preferred_cpu = get_nohz_load_balancer();
+                if (preferred_cpu >= 0)
+                        cpu = preferred_cpu;
+        }
+#endif
 
-        new_cpu_base = &__get_cpu_var(hrtimer_bases);
+again:
+        new_cpu_base = &per_cpu(hrtimer_bases, cpu);
         new_base = &new_cpu_base->clock_base[base->index];
 
         if (base != new_base) {
@@ -219,6 +232,40 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
                 timer->base = NULL;
                 spin_unlock(&base->cpu_base->lock);
                 spin_lock(&new_base->cpu_base->lock);
+
+                /* Optimized away for NOHZ=n SMP=n */
+                if (cpu == preferred_cpu) {
+                        /* Calculate clock monotonic expiry time */
+#ifdef CONFIG_HIGH_RES_TIMERS
+                        ktime_t expires = ktime_sub(hrtimer_get_expires(timer),
+                                                        new_base->offset);
+#else
+                        ktime_t expires = hrtimer_get_expires(timer);
+#endif
+
+                        /*
+                         * Get the next event on target cpu from the
+                         * clock events layer.
+                         * This covers the highres=off nohz=on case as well.
+                         */
+                        ktime_t next = clockevents_get_next_event(cpu);
+
+                        ktime_t delta = ktime_sub(expires, next);
+
+                        /*
+                         * We do not migrate the timer when it is expiring
+                         * before the next event on the target cpu because
+                         * we cannot reprogram the target cpu hardware and
+                         * we would cause it to fire late.
+                         */
+                        if (delta.tv64 < 0) {
+                                cpu = smp_processor_id();
+                                spin_unlock(&new_base->cpu_base->lock);
+                                spin_lock(&base->cpu_base->lock);
+                                timer->base = base;
+                                goto again;
+                        }
+                }
                 timer->base = new_base;
         }
         return new_base;
@@ -236,7 +283,7 @@ lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
         return base;
 }
 
-# define switch_hrtimer_base(t, b)      (b)
+# define switch_hrtimer_base(t, b, p)   (b)
 
 #endif  /* !CONFIG_SMP */