Re: [PATCH v9 05/32] tracing/timers: Add tracepoint for tracking timer base is_idle flag

Frederic Weisbecker
2023-12-20T13:43:55Z

Le Fri, Dec 01, 2023 at 10:26:27AM +0100, Anna-Maria Behnsen a écrit :
> 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>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

Just a detail below, again this can be posted as a delta patch or
edited before applying:

> ---
> v9: New in v9
> ---
> include/trace/events/timer.h | 20 ++++++++++++++++++++
> kernel/time/timer.c | 2 ++
> 2 files changed, 22 insertions(+)
>
> diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
> index 99ada928d445..1ef58a04fc57 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 a81d793a43d0..46a9b96a3976 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1964,6 +1964,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
> if ((expires - basem) > TICK_NSEC)
> base->is_idle = true;
> }
> + trace_timer_base_idle(base->is_idle, base->cpu);

This will trigger a trace everytime we loop into idle or remotely
compute the next timer. Can we move that to when base->is_idle is set
from false to true only?

> raw_spin_unlock(&base->lock);
>
> return cmp_next_hrtimer_event(basem, expires);
> @@ -1985,6 +1986,7 @@ void timer_clear_idle(void)
> * the lock in the exit from idle path.
> */
> base->is_idle = false;
> + trace_timer_base_idle(0, smp_processor_id());

Same here. If base->is_idle was already false, you could spare a noisy
trace.

Thanks.

> }
> #endif
>
> --
> 2.39.2
>