sched: x86, track TSC-unstable events

track TSC-unstable events and propagate it to the scheduler code.
Also allow sched_clock() to be used when the TSC is unstable,
the rq_clock() wrapper creates a reliable clock out of it.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -67,6 +67,13 @@ unsigned long long __attribute__((weak)) sched_clock(void)
 	return (unsigned long long)jiffies * (1000000000 / HZ);
 }
 
+/*
+ * CPU frequency is/was unstable - start new by setting prev_clock_raw:
+ */
+void sched_clock_unstable_event(void)
+{
+}
+
 /*
  * Convert user-nice values [ -20 ... 0 ... 19 ]
  * to static priority [ MAX_RT_PRIO..MAX_PRIO-1 ],