nohz: Use enum code for tick stop failure tracing message

It makes nohz tracing more lightweight, standard and easier to parse.

Examples:

       user_loop-2904  [007] d..1   517.701126: tick_stop: success=1 dependency=NONE
       user_loop-2904  [007] dn.1   518.021181: tick_stop: success=0 dependency=SCHED
    posix_timers-6142  [007] d..1  1739.027400: tick_stop: success=0 dependency=POSIX_TIMER
       user_loop-5463  [007] dN.1  1185.931939: tick_stop: success=0 dependency=PERF_EVENTS
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

include/linux/tick.h

@@ -104,6 +104,7 @@ enum tick_dep_bits {
 	TICK_DEP_BIT_CLOCK_UNSTABLE	= 3
 };
 
+#define TICK_DEP_MASK_NONE		0
 #define TICK_DEP_MASK_POSIX_TIMER	(1 << TICK_DEP_BIT_POSIX_TIMER)
 #define TICK_DEP_MASK_PERF_EVENTS	(1 << TICK_DEP_BIT_PERF_EVENTS)
 #define TICK_DEP_MASK_SCHED		(1 << TICK_DEP_BIT_SCHED)

include/trace/events/timer.h

@@ -328,23 +328,49 @@ TRACE_EVENT(itimer_expire,
 );
 
 #ifdef CONFIG_NO_HZ_COMMON
+
+#define TICK_DEP_NAMES					\
+		tick_dep_name(NONE)			\
+		tick_dep_name(POSIX_TIMER)		\
+		tick_dep_name(PERF_EVENTS)		\
+		tick_dep_name(SCHED)			\
+		tick_dep_name_end(CLOCK_UNSTABLE)
+
+#undef tick_dep_name
+#undef tick_dep_name_end
+
+#define tick_dep_name(sdep) TRACE_DEFINE_ENUM(TICK_DEP_MASK_##sdep);
+#define tick_dep_name_end(sdep)  TRACE_DEFINE_ENUM(TICK_DEP_MASK_##sdep);
+
+TICK_DEP_NAMES
+
+#undef tick_dep_name
+#undef tick_dep_name_end
+
+#define tick_dep_name(sdep) { TICK_DEP_MASK_##sdep, #sdep },
+#define tick_dep_name_end(sdep) { TICK_DEP_MASK_##sdep, #sdep }
+
+#define show_tick_dep_name(val)				\
+	__print_symbolic(val, TICK_DEP_NAMES)
+
 TRACE_EVENT(tick_stop,
 
-	TP_PROTO(int success, char *error_msg),
+	TP_PROTO(int success, int dependency),
 
-	TP_ARGS(success, error_msg),
+	TP_ARGS(success, dependency),
 
 	TP_STRUCT__entry(
 		__field( int ,		success	)
-		__string( msg, 		error_msg )
+		__field( int ,		dependency )
 	),
 
 	TP_fast_assign(
 		__entry->success	= success;
-		__assign_str(msg, error_msg);
+		__entry->dependency	= dependency;
 	),
 
-	TP_printk("success=%s msg=%s",  __entry->success ? "yes" : "no", __get_str(msg))
+	TP_printk("success=%d dependency=%s",  __entry->success, \
+			show_tick_dep_name(__entry->dependency))
 );
 #endif
 

kernel/time/tick-sched.c

@@ -163,22 +163,22 @@ static unsigned long tick_dep_mask;
 static void trace_tick_dependency(unsigned long dep)
 {
 	if (dep & TICK_DEP_MASK_POSIX_TIMER) {
-		trace_tick_stop(0, "posix timers running\n");
+		trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
 		return;
 	}
 
 	if (dep & TICK_DEP_MASK_PERF_EVENTS) {
-		trace_tick_stop(0, "perf events running\n");
+		trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
 		return;
 	}
 
 	if (dep & TICK_DEP_MASK_SCHED) {
-		trace_tick_stop(0, "more than 1 task in runqueue\n");
+		trace_tick_stop(0, TICK_DEP_MASK_SCHED);
 		return;
 	}
 
 	if (dep & TICK_DEP_MASK_CLOCK_UNSTABLE)
-		trace_tick_stop(0, "unstable sched clock\n");
+		trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
 }
 
 static bool can_stop_full_tick(struct tick_sched *ts)
@@ -206,17 +206,17 @@ static bool can_stop_full_tick(struct tick_sched *ts)
 	}
 
 	if (!sched_can_stop_tick()) {
-		trace_tick_stop(0, "more than 1 task in runqueue\n");
+		trace_tick_stop(0, TICK_DEP_MASK_SCHED);
 		return false;
 	}
 
 	if (!posix_cpu_timers_can_stop_tick(current)) {
-		trace_tick_stop(0, "posix timers running\n");
+		trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
 		return false;
 	}
 
 	if (!perf_event_can_stop_tick()) {
-		trace_tick_stop(0, "perf events running\n");
+		trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
 		return false;
 	}
 
@@ -228,7 +228,7 @@ static bool can_stop_full_tick(struct tick_sched *ts)
 	 * sched_clock_stable is set.
 	 */
 	if (!sched_clock_stable()) {
-		trace_tick_stop(0, "unstable sched clock\n");
+		trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
 		/*
 		 * Don't allow the user to think they can get
 		 * full NO_HZ with this machine.
@@ -821,7 +821,7 @@ 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, " ");
+		trace_tick_stop(1, TICK_DEP_MASK_NONE);
 	}
 
 	/*