sched: add optional support for CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

this replaces the rq->clock stuff (and possibly cpu_clock()).

 - architectures that have an 'imperfect' hardware clock can set
   CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

 - the 'jiffie' window might be superfulous when we update tick_gtod
   before the __update_sched_clock() call in sched_clock_tick()

 - cpu_clock() might be implemented as:

     sched_clock_cpu(smp_processor_id())

   if the accuracy proves good enough - how far can TSC drift in a
   single jiffie when considering the filtering and idle hooks?

[ mingo@elte.hu: various fixes and cleanups ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

7 files changed, 281 insertions, 161 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 54c9ca26b7d8..0c35b0343a76 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1553,6 +1553,35 @@ static inline int set_cpus_allowed(struct task_struct *p, cpumask_t new_mask)
 
 extern unsigned long long sched_clock(void);
 
+#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+static inline void sched_clock_init(void)
+{
+}
+
+static inline u64 sched_clock_cpu(int cpu)
+{
+        return sched_clock();
+}
+
+static inline void sched_clock_tick(void)
+{
+}
+
+static inline void sched_clock_idle_sleep_event(void)
+{
+}
+
+static inline void sched_clock_idle_wakeup_event(u64 delta_ns)
+{
+}
+#else
+extern void sched_clock_init(void);
+extern u64 sched_clock_cpu(int cpu);
+extern void sched_clock_tick(void);
+extern void sched_clock_idle_sleep_event(void);
+extern void sched_clock_idle_wakeup_event(u64 delta_ns);
+#endif
+
 /*
  * For kernel-internal use: high-speed (but slightly incorrect) per-cpu
  * clock constructed from sched_clock():
diff --git a/init/main.c b/init/main.c
index a87d4ca5c36c..ddada7acf363 100644
--- a/init/main.c
+++ b/init/main.c
@@ -602,6 +602,7 @@ asmlinkage void __init start_kernel(void)
         softirq_init();
         timekeeping_init();
         time_init();
+        sched_clock_init();
         profile_init();
         if (!irqs_disabled())
                 printk("start_kernel(): bug: interrupts were enabled early\n");
diff --git a/kernel/Makefile b/kernel/Makefile
index 188c43223f52..1c9938addb9d 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -9,7 +9,7 @@ obj-y     = sched.o fork.o exec_domain.o panic.o printk.o profile.o \
             rcupdate.o extable.o params.o posix-timers.o \
             kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
             hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
-            notifier.o ksysfs.o pm_qos_params.o
+            notifier.o ksysfs.o pm_qos_params.o sched_clock.o
 
 obj-$(CONFIG_SYSCTL_SYSCALL_CHECK) += sysctl_check.o
 obj-$(CONFIG_STACKTRACE) += stacktrace.o
diff --git a/kernel/sched.c b/kernel/sched.c
index 9457106b18af..58fb8af15776 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -75,16 +75,6 @@
 #include <asm/irq_regs.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);
-}
-
-/*
  * Convert user-nice values [ -20 ... 0 ... 19 ]
  * to static priority [ MAX_RT_PRIO..MAX_PRIO-1 ],
  * and back.
@@ -557,13 +547,7 @@ struct rq {
         unsigned long next_balance;
         struct mm_struct *prev_mm;
 
-        u64 clock, prev_clock_raw;
-        s64 clock_max_delta;
-
-        unsigned int clock_warps, clock_overflows, clock_underflows;
-        u64 idle_clock;
-        unsigned int clock_deep_idle_events;
-        u64 tick_timestamp;
+        u64 clock;
 
         atomic_t nr_iowait;
 
@@ -628,82 +612,6 @@ static inline int cpu_of(struct rq *rq)
 #endif
 }
 
-#ifdef CONFIG_NO_HZ
-static inline bool nohz_on(int cpu)
-{
-        return tick_get_tick_sched(cpu)->nohz_mode != NOHZ_MODE_INACTIVE;
-}
-
-static inline u64 max_skipped_ticks(struct rq *rq)
-{
-        return nohz_on(cpu_of(rq)) ? jiffies - rq->last_tick_seen + 2 : 1;
-}
-
-static inline void update_last_tick_seen(struct rq *rq)
-{
-        rq->last_tick_seen = jiffies;
-}
-#else
-static inline u64 max_skipped_ticks(struct rq *rq)
-{
-        return 1;
-}
-
-static inline void update_last_tick_seen(struct rq *rq)
-{
-}
-#endif
-
-/*
- * Update the per-runqueue clock, as finegrained as the platform can give
- * us, but without assuming monotonicity, etc.:
- */
-static void __update_rq_clock(struct rq *rq)
-{
-        u64 prev_raw = rq->prev_clock_raw;
-        u64 now = sched_clock();
-        s64 delta = now - prev_raw;
-        u64 clock = rq->clock;
-
-#ifdef CONFIG_SCHED_DEBUG
-        WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());
-#endif
-        /*
-         * Protect against sched_clock() occasionally going backwards:
-         */
-        if (unlikely(delta < 0)) {
-                clock++;
-                rq->clock_warps++;
-        } else {
-                /*
-                 * Catch too large forward jumps too:
-                 */
-                u64 max_jump = max_skipped_ticks(rq) * TICK_NSEC;
-                u64 max_time = rq->tick_timestamp + max_jump;
-
-                if (unlikely(clock + delta > max_time)) {
-                        if (clock < max_time)
-                                clock = max_time;
-                        else
-                                clock++;
-                        rq->clock_overflows++;
-                } else {
-                        if (unlikely(delta > rq->clock_max_delta))
-                                rq->clock_max_delta = delta;
-                        clock += delta;
-                }
-        }
-
-        rq->prev_clock_raw = now;
-        rq->clock = clock;
-}
-
-static void update_rq_clock(struct rq *rq)
-{
-        if (likely(smp_processor_id() == cpu_of(rq)))
-                __update_rq_clock(rq);
-}
-
 /*
  * The domain tree (rq->sd) is protected by RCU's quiescent state transition.
  * See detach_destroy_domains: synchronize_sched for details.
@@ -719,6 +627,11 @@ static void update_rq_clock(struct rq *rq)
 #define task_rq(p)              cpu_rq(task_cpu(p))
 #define cpu_curr(cpu)           (cpu_rq(cpu)->curr)
 
+static inline void update_rq_clock(struct rq *rq)
+{
+        rq->clock = sched_clock_cpu(cpu_of(rq));
+}
+
 /*
  * Tunables that become constants when CONFIG_SCHED_DEBUG is off:
  */
@@ -935,7 +848,6 @@ static unsigned long long __sync_cpu_clock(unsigned long long time, int cpu)
 static unsigned long long __cpu_clock(int cpu)
 {
         unsigned long long now;
-        struct rq *rq;
 
         /*
          * Only call sched_clock() if the scheduler has already been
@@ -944,9 +856,7 @@ static unsigned long long __cpu_clock(int cpu)
         if (unlikely(!scheduler_running))
                 return 0;
 
-        rq = cpu_rq(cpu);
-        update_rq_clock(rq);
-        now = rq->clock;
+        now = sched_clock_cpu(cpu);
 
         return now;
 }
@@ -1120,45 +1030,6 @@ static struct rq *this_rq_lock(void)
         return rq;
 }
 
-/*
- * We are going deep-idle (irqs are disabled):
- */
-void sched_clock_idle_sleep_event(void)
-{
-        struct rq *rq = cpu_rq(smp_processor_id());
-
-        WARN_ON(!irqs_disabled());
-        spin_lock(&rq->lock);
-        __update_rq_clock(rq);
-        spin_unlock(&rq->lock);
-        rq->clock_deep_idle_events++;
-}
-EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
-
-/*
- * We just idled delta nanoseconds (called with irqs disabled):
- */
-void sched_clock_idle_wakeup_event(u64 delta_ns)
-{
-        struct rq *rq = cpu_rq(smp_processor_id());
-        u64 now = sched_clock();
-
-        WARN_ON(!irqs_disabled());
-        rq->idle_clock += delta_ns;
-        /*
-         * 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:
-         */
-        spin_lock(&rq->lock);
-        rq->prev_clock_raw = now;
-        rq->clock += delta_ns;
-        spin_unlock(&rq->lock);
-        touch_softlockup_watchdog();
-}
-EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
-
 static void __resched_task(struct task_struct *p, int tif_bit);
 
 static inline void resched_task(struct task_struct *p)
@@ -1283,7 +1154,7 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)
         WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());
 
         spin_lock(&rq->lock);
-        __update_rq_clock(rq);
+        update_rq_clock(rq);
         rq->curr->sched_class->task_tick(rq, rq->curr, 1);
         spin_unlock(&rq->lock);
 
@@ -4476,19 +4347,11 @@ void scheduler_tick(void)
         int cpu = smp_processor_id();
         struct rq *rq = cpu_rq(cpu);
         struct task_struct *curr = rq->curr;
-        u64 next_tick = rq->tick_timestamp + TICK_NSEC;
+
+        sched_clock_tick();
 
         spin_lock(&rq->lock);
-        __update_rq_clock(rq);
-        /*
-         * Let rq->clock advance by at least TICK_NSEC:
-         */
-        if (unlikely(rq->clock < next_tick)) {
-                rq->clock = next_tick;
-                rq->clock_underflows++;
-        }
-        rq->tick_timestamp = rq->clock;
-        update_last_tick_seen(rq);
+        update_rq_clock(rq);
         update_cpu_load(rq);
         curr->sched_class->task_tick(rq, curr, 0);
         spin_unlock(&rq->lock);
@@ -4642,7 +4505,7 @@ need_resched_nonpreemptible:
          * Do the rq-clock update outside the rq lock:
          */
         local_irq_disable();
-        __update_rq_clock(rq);
+        update_rq_clock(rq);
         spin_lock(&rq->lock);
         clear_tsk_need_resched(prev);
 
@@ -8226,8 +8089,6 @@ void __init sched_init(void)
                 spin_lock_init(&rq->lock);
                 lockdep_set_class(&rq->lock, &rq->rq_lock_key);
                 rq->nr_running = 0;
-                rq->clock = 1;
-                update_last_tick_seen(rq);
                 init_cfs_rq(&rq->cfs, rq);
                 init_rt_rq(&rq->rt, rq);
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -8371,6 +8232,7 @@ EXPORT_SYMBOL(__might_sleep);
 static void normalize_task(struct rq *rq, struct task_struct *p)
 {
         int on_rq;
+
         update_rq_clock(rq);
         on_rq = p->se.on_rq;
         if (on_rq)
@@ -8402,7 +8264,6 @@ void normalize_rt_tasks(void)
                 p->se.sleep_start               = 0;
                 p->se.block_start               = 0;
 #endif
-                task_rq(p)->clock               = 0;
 
                 if (!rt_task(p)) {
                         /*
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
new file mode 100644
index 000000000000..9c597e37f7de
--- /dev/null
+++ b/kernel/sched_clock.c
@@ -0,0 +1,236 @@
+/*
+ * sched_clock for unstable cpu clocks
+ *
+ *  Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
+ *
+ * Based on code by:
+ *   Ingo Molnar <mingo@redhat.com>
+ *   Guillaume Chazarain <guichaz@gmail.com>
+ *
+ * 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.
+ *
+ * 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).
+ */
+#include <linux/sched.h>
+#include <linux/percpu.h>
+#include <linux/spinlock.h>
+#include <linux/ktime.h>
+#include <linux/module.h>
+
+
+#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+
+struct sched_clock_data {
+        /*
+         * Raw spinlock - this is a special case: this might be called
+         * from within instrumentation code so we dont want to do any
+         * instrumentation ourselves.
+         */
+        raw_spinlock_t          lock;
+
+        unsigned long           prev_jiffies;
+        u64                     prev_raw;
+        u64                     tick_raw;
+        u64                     tick_gtod;
+        u64                     clock;
+};
+
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
+
+static inline struct sched_clock_data *this_scd(void)
+{
+        return &__get_cpu_var(sched_clock_data);
+}
+
+static inline struct sched_clock_data *cpu_sdc(int cpu)
+{
+        return &per_cpu(sched_clock_data, cpu);
+}
+
+void sched_clock_init(void)
+{
+        u64 ktime_now = ktime_to_ns(ktime_get());
+        u64 now = 0;
+        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->prev_jiffies = jiffies;
+                scd->prev_raw = now;
+                scd->tick_raw = now;
+                scd->tick_gtod = ktime_now;
+                scd->clock = ktime_now;
+        }
+}
+
+/*
+ * 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)
+{
+        unsigned long now_jiffies = jiffies;
+        long delta_jiffies = now_jiffies - scd->prev_jiffies;
+        u64 clock = scd->clock;
+        u64 min_clock, max_clock;
+        s64 delta = now - scd->prev_raw;
+
+        WARN_ON_ONCE(!irqs_disabled());
+        min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC;
+
+        if (unlikely(delta < 0)) {
+                clock++;
+                goto out;
+        }
+
+        max_clock = min_clock + TICK_NSEC;
+
+        if (unlikely(clock + delta > max_clock)) {
+                if (clock < max_clock)
+                        clock = max_clock;
+                else
+                        clock++;
+        } else {
+                clock += delta;
+        }
+
+ out:
+        if (unlikely(clock < min_clock))
+                clock = min_clock;
+
+        scd->prev_raw = now;
+        scd->prev_jiffies = now_jiffies;
+        scd->clock = clock;
+}
+
+static void lock_double_clock(struct sched_clock_data *data1,
+                                struct sched_clock_data *data2)
+{
+        if (data1 < data2) {
+                __raw_spin_lock(&data1->lock);
+                __raw_spin_lock(&data2->lock);
+        } else {
+                __raw_spin_lock(&data2->lock);
+                __raw_spin_lock(&data1->lock);
+        }
+}
+
+u64 sched_clock_cpu(int cpu)
+{
+        struct sched_clock_data *scd = cpu_sdc(cpu);
+        u64 now, clock;
+
+        WARN_ON_ONCE(!irqs_disabled());
+        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;
+
+                now -= my_scd->tick_gtod;
+                now += scd->tick_gtod;
+
+                __raw_spin_unlock(&my_scd->lock);
+        } else {
+                __raw_spin_lock(&scd->lock);
+        }
+
+        __update_sched_clock(scd, now);
+        clock = scd->clock;
+
+        __raw_spin_unlock(&scd->lock);
+
+        return clock;
+}
+
+void sched_clock_tick(void)
+{
+        struct sched_clock_data *scd = this_scd();
+        u64 now, now_gtod;
+
+        WARN_ON_ONCE(!irqs_disabled());
+
+        now = sched_clock();
+        now_gtod = ktime_to_ns(ktime_get());
+
+        __raw_spin_lock(&scd->lock);
+        __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.
+         */
+        scd->tick_raw = now;
+        scd->tick_gtod = now_gtod;
+        __raw_spin_unlock(&scd->lock);
+}
+
+/*
+ * We are going deep-idle (irqs are disabled):
+ */
+void sched_clock_idle_sleep_event(void)
+{
+        sched_clock_cpu(smp_processor_id());
+}
+EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
+
+/*
+ * We just idled delta nanoseconds (called with irqs disabled):
+ */
+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;
+        __raw_spin_unlock(&scd->lock);
+
+        touch_softlockup_watchdog();
+}
+EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
+
+#endif
+
+/*
+ * 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);
+}
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index 6b4a12558e88..5f06118fbc31 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -204,13 +204,6 @@ static void print_cpu(struct seq_file *m, int cpu)
         PN(next_balance);
         P(curr->pid);
         PN(clock);
-        PN(idle_clock);
-        PN(prev_clock_raw);
-        P(clock_warps);
-        P(clock_overflows);
-        P(clock_underflows);
-        P(clock_deep_idle_events);
-        PN(clock_max_delta);
         P(cpu_load[0]);
         P(cpu_load[1]);
         P(cpu_load[2]);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index d99e01f6929a..c863663d204d 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -959,7 +959,7 @@ static void yield_task_fair(struct rq *rq)
                 return;
 
         if (likely(!sysctl_sched_compat_yield) && curr->policy != SCHED_BATCH) {
-                __update_rq_clock(rq);
+                update_rq_clock(rq);
                 /*
                  * Update run-time statistics of the 'current'.
                  */