ftrace: use cpu clock again

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/trace/trace.c

@@ -42,61 +42,9 @@ ns2usecs(cycle_t nsec)
 	return nsec;
 }
 
-static const int time_sync_freq_max = 128;
-static const cycle_t time_sync_thresh = 100000;
-
-static DEFINE_PER_CPU(cycle_t, time_offset);
-static DEFINE_PER_CPU(cycle_t, prev_cpu_time);
-static DEFINE_PER_CPU(int, time_sync_count);
-static DEFINE_PER_CPU(int, time_sync_freq);
-
-/*
- * 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 cycle_t prev_global_time;
-
-static notrace cycle_t __ftrace_now_sync(cycles_t time, int cpu)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&time_sync_lock, flags);
-
-	/*
-	 * Update the synchronization frequency:
-	 */
-	if (per_cpu(time_sync_freq, cpu) < time_sync_freq_max)
-		per_cpu(time_sync_freq, cpu) *= 2;
-	per_cpu(time_sync_count, cpu) = per_cpu(time_sync_freq, cpu);
-
-	if (time < prev_global_time) {
-		per_cpu(time_offset, cpu) += prev_global_time - time;
-		time = prev_global_time;
-	} else {
-		prev_global_time = time;
-	}
-
-	spin_unlock_irqrestore(&time_sync_lock, flags);
-
-	return time;
-}
-
 notrace cycle_t ftrace_now(int cpu)
 {
-	cycle_t prev_cpu_time, time, delta_time;
-
-	prev_cpu_time = per_cpu(prev_cpu_time, cpu);
-	time = sched_clock() + per_cpu(time_offset, cpu);
-	delta_time = time-prev_cpu_time;
-
-	if (unlikely(delta_time > time_sync_thresh ||
-				--per_cpu(time_sync_count, cpu) <= 0))
-		time = __ftrace_now_sync(time, cpu);
-
-	return time;
+	return cpu_clock(cpu);
 }
 
 static struct trace_array	global_trace;