1 files changed, 71 insertions, 153 deletions

diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index 22ed55d1167f..e8ab096ddfe3 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -12,19 +12,17 @@
  *
  * Create a semi stable clock from a mixture of other events, including:
  *  - gtod
- *  - jiffies
  *  - sched_clock()
  *  - explicit idle events
  *
  * We use gtod as base and the unstable clock deltas. The deltas are filtered,
- * making it monotonic and keeping it within an expected window.  This window
- * is set up using jiffies.
+ * making it monotonic and keeping it within an expected window.
  *
  * Furthermore, explicit sleep and wakeup hooks allow us to account for time
  * that is otherwise invisible (TSC gets stopped).
  *
  * The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
- * consistent between cpus (never more than 1 jiffies difference).
+ * consistent between cpus (never more than 2 jiffies difference).
  */
 #include <linux/sched.h>
 #include <linux/percpu.h>
@@ -32,13 +30,19 @@
 #include <linux/ktime.h>
 #include <linux/module.h>
 
+/*
+ * Scheduler clock - returns current time in nanosec units.
+ * This is default implementation.
+ * Architectures and sub-architectures can override this.
+ */
+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 {
         /*
@@ -48,15 +52,9 @@ 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);
@@ -71,121 +69,69 @@ 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());
-        unsigned long now_jiffies = jiffies;
         int cpu;
 
         for_each_possible_cpu(cpu) {
                 struct sched_clock_data *scd = cpu_sdc(cpu);
 
                 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.
+ * min,max except they take wrapping into account
  */
-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)
+static inline u64 wrap_min(u64 x, u64 y)
 {
-        struct sched_clock_data *scd = cpu_sdc(cpu);
-
-        scd->check_max = 1;
+        return (s64)(x - y) < 0 ? x : y;
 }
 
-static int check_max(struct sched_clock_data *scd)
+static inline u64 wrap_max(u64 x, u64 y)
 {
-        return scd->check_max;
+        return (s64)(x - y) > 0 ? x : y;
 }
-#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
+ *  - use the GTOD tick value to create a window to filter crazy TSC 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;
+        u64 clock, min_clock, max_clock;
 
         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;
-
-        if (unlikely(delta < 0)) {
-                clock++;
-                goto out;
-        }
+        if (unlikely(delta < 0))
+                delta = 0;
 
         /*
-         * 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.
+         * scd->clock = clamp(scd->tick_gtod + delta,
+         *                    max(scd->tick_gtod, scd->clock),
+         *                    scd->tick_gtod + TICK_NSEC);
          */
-        max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC;
 
-        delta *= scd->multi;
-        delta >>= MULTI_SHIFT;
+        clock = scd->tick_gtod + delta;
+        min_clock = wrap_max(scd->tick_gtod, scd->clock);
+        max_clock = scd->tick_gtod + TICK_NSEC;
 
-        if (unlikely(clock + delta > max_clock) && check_max(scd)) {
-                if (clock < max_clock)
-                        clock = max_clock;
-                else
-                        clock++;
-        } else {
-                clock += delta;
-        }
+        clock = wrap_max(clock, min_clock);
+        clock = wrap_min(clock, max_clock);
 
- out:
-        if (unlikely(clock < min_clock))
-                clock = min_clock;
+        scd->clock = clock;
 
-        if (time)
-                *time = clock;
-        else {
-                scd->prev_raw = now;
-                scd->clock = clock;
-        }
+        return scd->clock;
 }
 
 static void lock_double_clock(struct sched_clock_data *data1,
@@ -203,7 +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;
@@ -212,43 +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((s64)(remote_clock - this_clock) < 0)) {
+                        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))
@@ -260,29 +207,9 @@ void sched_clock_tick(void)
         now = sched_clock();
 
         __raw_spin_lock(&scd->lock);
-        __update_sched_clock(scd, now, NULL);
-        /*
-         * 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;
+        __update_sched_clock(scd, now);
         __raw_spin_unlock(&scd->lock);
 }
 
@@ -300,37 +227,28 @@ 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
-         * sched_clock() deltas that occured while we idled,
-         * and use the PM-provided delta_ns to advance the
-         * 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);
-
+        sched_clock_tick();
         touch_softlockup_watchdog();
 }
 EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
 
-#endif
+#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
 
-/*
- * Scheduler clock - returns current time in nanosec units.
- * This is default implementation.
- * Architectures and sub-architectures can override this.
- */
-unsigned long long __attribute__((weak)) sched_clock(void)
+void sched_clock_init(void)
 {
-        return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
+        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)
 {
         unsigned long long clock;