2 files changed, 49 insertions, 116 deletions

diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index 5a2dc7d8fd98..204991a0bfa7 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -42,12 +42,9 @@ unsigned long long __attribute__((weak)) sched_clock(void)
         return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
 }
 
-#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+static __read_mostly int sched_clock_running;
 
-#define MULTI_SHIFT 15
-/* Max is double, Min is 1/2 */
-#define MAX_MULTI (2LL << MULTI_SHIFT)
-#define MIN_MULTI (1LL << (MULTI_SHIFT-1))
+#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
 
 struct sched_clock_data {
         /*
@@ -58,14 +55,9 @@ struct sched_clock_data {
         raw_spinlock_t          lock;
 
         unsigned long           tick_jiffies;
-        u64                     prev_raw;
         u64                     tick_raw;
         u64                     tick_gtod;
         u64                     clock;
-        s64                     multi;
-#ifdef CONFIG_NO_HZ
-        int                     check_max;
-#endif
 };
 
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
@@ -80,8 +72,6 @@ static inline struct sched_clock_data *cpu_sdc(int cpu)
         return &per_cpu(sched_clock_data, cpu);
 }
 
-static __read_mostly int sched_clock_running;
-
 void sched_clock_init(void)
 {
         u64 ktime_now = ktime_to_ns(ktime_get());
@@ -93,90 +83,39 @@ void sched_clock_init(void)
 
                 scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
                 scd->tick_jiffies = now_jiffies;
-                scd->prev_raw = 0;
                 scd->tick_raw = 0;
                 scd->tick_gtod = ktime_now;
                 scd->clock = ktime_now;
-                scd->multi = 1 << MULTI_SHIFT;
-#ifdef CONFIG_NO_HZ
-                scd->check_max = 1;
-#endif
         }
 
         sched_clock_running = 1;
 }
 
-#ifdef CONFIG_NO_HZ
-/*
- * The dynamic ticks makes the delta jiffies inaccurate. This
- * prevents us from checking the maximum time update.
- * Disable the maximum check during stopped ticks.
- */
-void sched_clock_tick_stop(int cpu)
-{
-        struct sched_clock_data *scd = cpu_sdc(cpu);
-
-        scd->check_max = 0;
-}
-
-void sched_clock_tick_start(int cpu)
-{
-        struct sched_clock_data *scd = cpu_sdc(cpu);
-
-        scd->check_max = 1;
-}
-
-static int check_max(struct sched_clock_data *scd)
-{
-        return scd->check_max;
-}
-#else
-static int check_max(struct sched_clock_data *scd)
-{
-        return 1;
-}
-#endif /* CONFIG_NO_HZ */
-
 /*
  * update the percpu scd from the raw @now value
  *
  *  - filter out backward motion
  *  - use jiffies to generate a min,max window to clip the raw values
  */
-static void __update_sched_clock(struct sched_clock_data *scd, u64 now, u64 *time)
+static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
 {
         unsigned long now_jiffies = jiffies;
         long delta_jiffies = now_jiffies - scd->tick_jiffies;
         u64 clock = scd->clock;
         u64 min_clock, max_clock;
-        s64 delta = now - scd->prev_raw;
+        s64 delta = now - scd->tick_raw;
 
         WARN_ON_ONCE(!irqs_disabled());
-
-        /*
-         * At schedule tick the clock can be just under the gtod. We don't
-         * want to push it too prematurely.
-         */
-        min_clock = scd->tick_gtod + (delta_jiffies * TICK_NSEC);
-        if (min_clock > TICK_NSEC)
-                min_clock -= TICK_NSEC / 2;
+        min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC;
 
         if (unlikely(delta < 0)) {
                 clock++;
                 goto out;
         }
 
-        /*
-         * The clock must stay within a jiffie of the gtod.
-         * But since we may be at the start of a jiffy or the end of one
-         * we add another jiffy buffer.
-         */
-        max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC;
-
-        delta *= scd->multi;
-        delta >>= MULTI_SHIFT;
+        max_clock = min_clock + TICK_NSEC;
 
-        if (unlikely(clock + delta > max_clock) && check_max(scd)) {
+        if (unlikely(clock + delta > max_clock)) {
                 if (clock < max_clock)
                         clock = max_clock;
                 else
@@ -189,12 +128,10 @@ static void __update_sched_clock(struct sched_clock_data *scd, u64 now, u64 *tim
         if (unlikely(clock < min_clock))
                 clock = min_clock;
 
-        if (time)
-                *time = clock;
-        else {
-                scd->prev_raw = now;
-                scd->clock = clock;
-        }
+        scd->tick_jiffies = now_jiffies;
+        scd->clock = clock;
+
+        return clock;
 }
 
 static void lock_double_clock(struct sched_clock_data *data1,
@@ -212,7 +149,7 @@ static void lock_double_clock(struct sched_clock_data *data1,
 u64 sched_clock_cpu(int cpu)
 {
         struct sched_clock_data *scd = cpu_sdc(cpu);
-        u64 now, clock;
+        u64 now, clock, this_clock, remote_clock;
 
         if (unlikely(!sched_clock_running))
                 return 0ull;
@@ -221,43 +158,44 @@ u64 sched_clock_cpu(int cpu)
         now = sched_clock();
 
         if (cpu != raw_smp_processor_id()) {
-                /*
-                 * in order to update a remote cpu's clock based on our
-                 * unstable raw time rebase it against:
-                 *   tick_raw           (offset between raw counters)
-                 *   tick_gotd          (tick offset between cpus)
-                 */
                 struct sched_clock_data *my_scd = this_scd();
 
                 lock_double_clock(scd, my_scd);
 
-                now -= my_scd->tick_raw;
-                now += scd->tick_raw;
+                this_clock = __update_sched_clock(my_scd, now);
+                remote_clock = scd->clock;
 
-                now += my_scd->tick_gtod;
-                now -= scd->tick_gtod;
+                /*
+                 * Use the opportunity that we have both locks
+                 * taken to couple the two clocks: we take the
+                 * larger time as the latest time for both
+                 * runqueues. (this creates monotonic movement)
+                 */
+                if (likely(remote_clock < this_clock)) {
+                        clock = this_clock;
+                        scd->clock = clock;
+                } else {
+                        /*
+                         * Should be rare, but possible:
+                         */
+                        clock = remote_clock;
+                        my_scd->clock = remote_clock;
+                }
 
                 __raw_spin_unlock(&my_scd->lock);
-
-                __update_sched_clock(scd, now, &clock);
-
-                __raw_spin_unlock(&scd->lock);
-
         } else {
                 __raw_spin_lock(&scd->lock);
-                __update_sched_clock(scd, now, NULL);
-                clock = scd->clock;
-                __raw_spin_unlock(&scd->lock);
+                clock = __update_sched_clock(scd, now);
         }
 
+        __raw_spin_unlock(&scd->lock);
+
         return clock;
 }
 
 void sched_clock_tick(void)
 {
         struct sched_clock_data *scd = this_scd();
-        unsigned long now_jiffies = jiffies;
-        s64 mult, delta_gtod, delta_raw;
         u64 now, now_gtod;
 
         if (unlikely(!sched_clock_running))
@@ -269,29 +207,14 @@ void sched_clock_tick(void)
         now = sched_clock();
 
         __raw_spin_lock(&scd->lock);
-        __update_sched_clock(scd, now, NULL);
+        __update_sched_clock(scd, now);
         /*
          * update tick_gtod after __update_sched_clock() because that will
          * already observe 1 new jiffy; adding a new tick_gtod to that would
          * increase the clock 2 jiffies.
          */
-        delta_gtod = now_gtod - scd->tick_gtod;
-        delta_raw = now - scd->tick_raw;
-
-        if ((long)delta_raw > 0) {
-                mult = delta_gtod << MULTI_SHIFT;
-                do_div(mult, delta_raw);
-                scd->multi = mult;
-                if (scd->multi > MAX_MULTI)
-                        scd->multi = MAX_MULTI;
-                else if (scd->multi < MIN_MULTI)
-                        scd->multi = MIN_MULTI;
-        } else
-                scd->multi = 1 << MULTI_SHIFT;
-
         scd->tick_raw = now;
         scd->tick_gtod = now_gtod;
-        scd->tick_jiffies = now_jiffies;
         __raw_spin_unlock(&scd->lock);
 }
 
@@ -310,7 +233,6 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
 void sched_clock_idle_wakeup_event(u64 delta_ns)
 {
         struct sched_clock_data *scd = this_scd();
-        u64 now = sched_clock();
 
         /*
          * Override the previous timestamp and ignore all
@@ -319,15 +241,28 @@ void sched_clock_idle_wakeup_event(u64 delta_ns)
          * rq clock:
          */
         __raw_spin_lock(&scd->lock);
-        scd->prev_raw = now;
         scd->clock += delta_ns;
-        scd->multi = 1 << MULTI_SHIFT;
         __raw_spin_unlock(&scd->lock);
 
         touch_softlockup_watchdog();
 }
 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
 
+#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
+
+void sched_clock_init(void)
+{
+        sched_clock_running = 1;
+}
+
+u64 sched_clock_cpu(int cpu)
+{
+        if (unlikely(!sched_clock_running))
+                return 0;
+
+        return sched_clock();
+}
+
 #endif
 
 unsigned long long cpu_clock(int cpu)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 825b4c00fe44..f5da526424a9 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -289,7 +289,6 @@ void tick_nohz_stop_sched_tick(int inidle)
                         ts->tick_stopped = 1;
                         ts->idle_jiffies = last_jiffies;
                         rcu_enter_nohz();
-                        sched_clock_tick_stop(cpu);
                 }
 
                 /*
@@ -392,7 +391,6 @@ void tick_nohz_restart_sched_tick(void)
         select_nohz_load_balancer(0);
         now = ktime_get();
         tick_do_update_jiffies64(now);
-        sched_clock_tick_start(cpu);
         cpu_clear(cpu, nohz_cpu_mask);
 
         /*