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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: Frederic 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>
This commit is contained in:
Frederic Weisbecker 2013-04-20 17:35:50 +02:00
parent 0637e02939
commit cb41a29076
2 changed files with 36 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
include/trace/events/timer.h
View File

@ -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 */

19
kernel/time/tick-sched.c
View File

@ -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, " ");
}
/*