sched: sched_clock_cpu() based cpu_clock()

with sched_clock_cpu() being reasonably in sync between cpus (max 1 jiffy
difference) use this to provide cpu_clock().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -818,82 +818,6 @@ static inline u64 global_rt_runtime(void)
 	return (u64)sysctl_sched_rt_runtime * NSEC_PER_USEC;
 }
 
-unsigned long long time_sync_thresh = 100000;
-
-static DEFINE_PER_CPU(unsigned long long, time_offset);
-static DEFINE_PER_CPU(unsigned long long, prev_cpu_time);
-
-/*
- * Global lock which we take every now and then to synchronize
- * the CPUs time. This method is not warp-safe, but it's good
- * enough to synchronize slowly diverging time sources and thus
- * it's good enough for tracing:
- */
-static DEFINE_SPINLOCK(time_sync_lock);
-static unsigned long long prev_global_time;
-
-static unsigned long long __sync_cpu_clock(unsigned long long time, int cpu)
-{
-	/*
-	 * We want this inlined, to not get tracer function calls
-	 * in this critical section:
-	 */
-	spin_acquire(&time_sync_lock.dep_map, 0, 0, _THIS_IP_);
-	__raw_spin_lock(&time_sync_lock.raw_lock);
-
-	if (time < prev_global_time) {
-		per_cpu(time_offset, cpu) += prev_global_time - time;
-		time = prev_global_time;
-	} else {
-		prev_global_time = time;
-	}
-
-	__raw_spin_unlock(&time_sync_lock.raw_lock);
-	spin_release(&time_sync_lock.dep_map, 1, _THIS_IP_);
-
-	return time;
-}
-
-static unsigned long long __cpu_clock(int cpu)
-{
-	unsigned long long now;
-
-	/*
-	 * Only call sched_clock() if the scheduler has already been
-	 * initialized (some code might call cpu_clock() very early):
-	 */
-	if (unlikely(!scheduler_running))
-		return 0;
-
-	now = sched_clock_cpu(cpu);
-
-	return now;
-}
-
-/*
- * For kernel-internal use: high-speed (but slightly incorrect) per-cpu
- * clock constructed from sched_clock():
- */
-unsigned long long cpu_clock(int cpu)
-{
-	unsigned long long prev_cpu_time, time, delta_time;
-	unsigned long flags;
-
-	local_irq_save(flags);
-	prev_cpu_time = per_cpu(prev_cpu_time, cpu);
-	time = __cpu_clock(cpu) + per_cpu(time_offset, cpu);
-	delta_time = time-prev_cpu_time;
-
-	if (unlikely(delta_time > time_sync_thresh)) {
-		time = __sync_cpu_clock(time, cpu);
-		per_cpu(prev_cpu_time, cpu) = time;
-	}
-	local_irq_restore(flags);
-
-	return time;
-}
-EXPORT_SYMBOL_GPL(cpu_clock);
-
 #ifndef prepare_arch_switch
 # define prepare_arch_switch(next)	do { } while (0)
 #endif

kernel/sched_clock.c

@@ -244,3 +244,15 @@ unsigned long long __attribute__((weak)) sched_clock(void)
 {
 	return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
 }
+
+unsigned long long cpu_clock(int cpu)
+{
+	unsigned long long clock;
+	unsigned long flags;
+
+	raw_local_irq_save(flags);
+	clock = sched_clock_cpu(cpu);
+	raw_local_irq_restore(flags);
+
+	return clock;
+}