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>

1 files changed, 13 insertions, 152 deletions

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)) {
                         /*