Merge branch 'timers/nohz-help-testing' of git://git.kernel.org/pub/s…

…cm/linux/kernel/git/frederic/linux-dynticks into timers/nohz

Pull full dynticks helpers from Frederic Weisbecker:

 - handy tracepoints that allow dynticks analysis,
   to answer "why does my tick not stop??" questions

 - select CONFIG_RCU_NOCB_ALL

Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/trace/events/timer.h

@@ -323,6 +323,27 @@ TRACE_EVENT(itimer_expire,
 		  (int) __entry->pid, (unsigned long long)__entry->now)
 );
 
+#ifdef CONFIG_NO_HZ_FULL
+TRACE_EVENT(tick_stop,
+
+	TP_PROTO(int success, char *error_msg),
+
+	TP_ARGS(success, error_msg),
+
+	TP_STRUCT__entry(
+		__field( int ,		success	)
+		__string( msg, 		error_msg )
+	),
+
+	TP_fast_assign(
+		__entry->success	= success;
+		__assign_str(msg, error_msg);
+	),
+
+	TP_printk("success=%s msg=%s",  __entry->success ? "yes" : "no", __get_str(msg))
+);
+#endif
+
 #endif /*  _TRACE_TIMER_H */
 
 /* This part must be outside protection */

kernel/time/Kconfig

@@ -110,6 +110,7 @@ config NO_HZ_FULL
 	select NO_HZ_COMMON
 	select RCU_USER_QS
 	select RCU_NOCB_CPU
+	select RCU_NOCB_CPU_ALL
 	select CONTEXT_TRACKING_FORCE
 	select IRQ_WORK
 	help

kernel/time/tick-sched.c

@@ -28,6 +28,8 @@
 
 #include "tick-internal.h"
 
+#include <trace/events/timer.h>
+
 /*
  * Per cpu nohz control structure
  */
@@ -153,23 +155,31 @@ static bool can_stop_full_tick(void)
 {
 	WARN_ON_ONCE(!irqs_disabled());
 
-	if (!sched_can_stop_tick())
+	if (!sched_can_stop_tick()) {
+		trace_tick_stop(0, "more than 1 task in runqueue\n");
 		return false;
+	}
 
-	if (!posix_cpu_timers_can_stop_tick(current))
+	if (!posix_cpu_timers_can_stop_tick(current)) {
+		trace_tick_stop(0, "posix timers running\n");
 		return false;
+	}
 
-	if (!perf_event_can_stop_tick())
+	if (!perf_event_can_stop_tick()) {
+		trace_tick_stop(0, "perf events running\n");
 		return false;
+	}
 
 	/* sched_clock_tick() needs us? */
 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
 	/*
 	 * TODO: kick full dynticks CPUs when
 	 * sched_clock_stable is set.
 	 */
-	if (!sched_clock_stable)
+	if (!sched_clock_stable) {
+		trace_tick_stop(0, "unstable sched clock\n");
 		return false;
+	}
 #endif
 
 	return true;
@@ -631,6 +641,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
 
 			ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
 			ts->tick_stopped = 1;
+			trace_tick_stop(1, " ");
 		}
 
 		/*