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Commit cb41a290 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

nohz: Add basic tracing 



It's not obvious to find out why the full dynticks subsystem
doesn't always stop the tick: whether this is due to kthreads,
posix timers, perf events, etc...

These new tracepoints are here to help the user diagnose
the failures and test this feature.

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
parent 0637e029

include/trace/events/timer.h

+21 −0
Original line number Diff line number Diff line
@@ -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/tick-sched.c

+15 −4
Original line number Diff line number Diff line
@@ -28,6 +28,8 @@ 


#include "tick-internal.h"



#include <trace/events/timer.h>



/*

 * Per cpu nohz control structure

 */
@@ -153,14 +155,20 @@ 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
@@ -168,8 +176,10 @@ static bool can_stop_full_tick(void) 
	 * 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, " ");

		}



		/*