1 files changed, 64 insertions, 46 deletions

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 052a0f53e4eb..e2f91ecc01a8 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -135,6 +135,46 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
         }
 }
 
+
+/*
+ * Get the preferred target CPU for NOHZ
+ */
+static int hrtimer_get_target(int this_cpu, int pinned)
+{
+#ifdef CONFIG_NO_HZ
+        if (!pinned && get_sysctl_timer_migration() && idle_cpu(this_cpu)) {
+                int preferred_cpu = get_nohz_load_balancer();
+
+                if (preferred_cpu >= 0)
+                        return preferred_cpu;
+        }
+#endif
+        return this_cpu;
+}
+
+/*
+ * With HIGHRES=y 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.
+ *
+ * Called with cpu_base->lock of target cpu held.
+ */
+static int
+hrtimer_check_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base)
+{
+#ifdef CONFIG_HIGH_RES_TIMERS
+        ktime_t expires;
+
+        if (!new_base->cpu_base->hres_active)
+                return 0;
+
+        expires = ktime_sub(hrtimer_get_expires(timer), new_base->offset);
+        return expires.tv64 <= new_base->cpu_base->expires_next.tv64;
+#else
+        return 0;
+#endif
+}
+
 /*
  * Switch the timer base to the current CPU when possible.
  */
@@ -144,16 +184,8 @@ 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
+        int this_cpu = smp_processor_id();
+        int cpu = hrtimer_get_target(this_cpu, pinned);
 
 again:
         new_cpu_base = &per_cpu(hrtimer_bases, cpu);
@@ -161,7 +193,7 @@ again:
 
         if (base != new_base) {
                 /*
-                 * We are trying to schedule the timer on the local CPU.
+                 * We are trying to move timer to new_base.
                  * However we can't change timer's base while it is running,
                  * so we keep it on the same CPU. No hassle vs. reprogramming
                  * the event source in the high resolution case. The softirq
@@ -177,38 +209,12 @@ again:
                 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;
-                        }
+                if (cpu != this_cpu && hrtimer_check_target(timer, new_base)) {
+                        cpu = this_cpu;
+                        spin_unlock(&new_base->cpu_base->lock);
+                        spin_lock(&base->cpu_base->lock);
+                        timer->base = base;
+                        goto again;
                 }
                 timer->base = new_base;
         }
@@ -1219,14 +1225,22 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 
         expires_next.tv64 = KTIME_MAX;
 
+        spin_lock(&cpu_base->lock);
+        /*
+         * We set expires_next to KTIME_MAX here with cpu_base->lock
+         * held to prevent that a timer is enqueued in our queue via
+         * the migration code. This does not affect enqueueing of
+         * timers which run their callback and need to be requeued on
+         * this CPU.
+         */
+        cpu_base->expires_next.tv64 = KTIME_MAX;
+
         base = cpu_base->clock_base;
 
         for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
                 ktime_t basenow;
                 struct rb_node *node;
 
-                spin_lock(&cpu_base->lock);
-
                 basenow = ktime_add(now, base->offset);
 
                 while ((node = base->first)) {
@@ -1259,11 +1273,15 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 
                         __run_hrtimer(timer);
                 }
-                spin_unlock(&cpu_base->lock);
                 base++;
         }
 
+        /*
+         * Store the new expiry value so the migration code can verify
+         * against it.
+         */
         cpu_base->expires_next = expires_next;
+        spin_unlock(&cpu_base->lock);
 
         /* Reprogramming necessary ? */
         if (expires_next.tv64 != KTIME_MAX) {