linux-kernel - Re: [PATCH v9 05/32] tracing/timers: Add tracepoint for tracking timer base is

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Message-ID: <ZYLvl06i0zIZfclG@localhost.localdomain>
Date: Wed, 20 Dec 2023 14:43:51 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
	John Stultz <jstultz@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Eric Dumazet <edumazet@...gle.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Arjan van de Ven <arjan@...radead.org>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Rik van Riel <riel@...riel.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sebastian Siewior <bigeasy@...utronix.de>,
	Giovanni Gherdovich <ggherdovich@...e.cz>,
	Lukasz Luba <lukasz.luba@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>,
	Srinivas Pandruvada <srinivas.pandruvada@...el.com>,
	K Prateek Nayak <kprateek.nayak@....com>
Subject: Re: [PATCH v9 05/32] tracing/timers: Add tracepoint for tracking
 timer base is_idle flag

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@...utronix.de>

Reviewed-by: Frederic Weisbecker <frederic@...nel.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
>