[tip: timers/core] tracing/timers: Add tracepoint for tracking timer base is_idle flag

tip-bot2 for Anna-Maria Behnsen
2023-12-20T15:59:12Z

The following commit has been merged into the timers/core branch of tip:

Commit-ID: b573c73101d8786446535b2ab28cbc8907bda9a9
Gitweb: https://git.kernel.org/tip/b573c73101d8786446535b2ab28cbc8907bda9a9
Author: Anna-Maria Behnsen <anna-maria@linutronix.de>
AuthorDate: Fri, 01 Dec 2023 10:26:27 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 20 Dec 2023 16:49:38 +01:00

tracing/timers: Add tracepoint for tracking timer base is_idle flag

When debugging timer code the timer tracepoints are very important. There
is no tracepoint when the is_idle flag of the timer base changes. Instead
of always adding manually trace_printk(), add tracepoints which can be
easily enabled whenever required.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20231201092654.34614-6-anna-maria@linutronix.de

---
include/trace/events/timer.h | 20 ++++++++++++++++++++
kernel/time/timer.c | 14 +++++++++++---
2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
index 99ada92..1ef58a0 100644
--- a/include/trace/events/timer.h
+++ b/include/trace/events/timer.h
@@ -142,6 +142,26 @@ DEFINE_EVENT(timer_class, timer_cancel,
TP_ARGS(timer)
);

+TRACE_EVENT(timer_base_idle,
+
+ TP_PROTO(bool is_idle, unsigned int cpu),
+
+ TP_ARGS(is_idle, cpu),
+
+ TP_STRUCT__entry(
+ __field( bool, is_idle )
+ __field( unsigned int, cpu )
+ ),
+
+ TP_fast_assign(
+ __entry->is_idle = is_idle;
+ __entry->cpu = cpu;
+ ),
+
+ TP_printk("is_idle=%d cpu=%d",
+ __entry->is_idle, __entry->cpu)
+);
+
#define decode_clockid(type) \
__print_symbolic(type, \
{ CLOCK_REALTIME, "CLOCK_REALTIME" }, \
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index a81d793..ed8d606 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1950,7 +1950,10 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)

if (time_before_eq(nextevt, basej)) {
expires = basem;
- base->is_idle = false;
+ if (base->is_idle) {
+ base->is_idle = false;
+ trace_timer_base_idle(false, base->cpu);
+ }
} else {
if (base->timers_pending)
expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
@@ -1961,8 +1964,10 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
* logic is only maintained for the BASE_STD base, deferrable
* timers may still see large granularity skew (by design).
*/
- if ((expires - basem) > TICK_NSEC)
+ if ((expires - basem) > TICK_NSEC && !base->is_idle) {
base->is_idle = true;
+ trace_timer_base_idle(true, base->cpu);
+ }
}
raw_spin_unlock(&base->lock);

@@ -1984,7 +1989,10 @@ void timer_clear_idle(void)
* sending the IPI a few instructions smaller for the cost of taking
* the lock in the exit from idle path.
*/
- base->is_idle = false;
+ if (base->is_idle) {
+ base->is_idle = false;
+ trace_timer_base_idle(false, smp_processor_id());
+ }
}
#endif