linux-kernel - Re: [PATCH] rtc: Add tracepoints for RTC system

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Date:   Wed, 15 Nov 2017 09:35:05 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     a.zummo@...ertech.it, alexandre.belloni@...e-electrons.com,
        rostedt@...dmis.org, mingo@...hat.com, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org, arnd@...db.de, broonie@...nel.org
Subject: Re: [PATCH] rtc: Add tracepoints for RTC system


* Baolin Wang <baolin.wang@...aro.org> wrote:

> It will be more helpful to add some tracepoints to track RTC actions when
> debugging RTC driver. Below sample is that we set/read the RTC time, then
> set 2 alarms, so we can see the trace logs:
> 
> set/read RTC time:
> kworker/1:1-586   [001] .... 21.826112: rtc_set_time: 2017-11-10 08:13:00 UTC (1510301580)
> kworker/1:1-586   [001] .... 21.826174: rtc_read_time: 2017-11-10 08:13:00 UTC (1510301580)
> 
> set the first alarm timer:
> kworker/1:1-586   [001] .... 21.841098: rtc_timer_enqueue: RTC timer:(ffffffc15ad913c8) 2017-11-10 08:15:00 UTC (1510301700)
> kworker/1:1-586   [001] .... 22.009424: rtc_set_alarm: 2017-11-10 08:15:00 UTC (1510301700)
> 
> set the second alarm timer:
> kworker/1:1-586   [001] .... 22.181304: rtc_timer_enqueue: RTC timer:(ffffff80088e6430) 2017-11-10 08:17:00 UTC (1510301820)
> 
> the first alarm timer was expired:
> kworker/0:1-67    [000] .... 145.156226: rtc_timer_dequeue: RTC timer:(ffffffc15ad913c8) 2017-11-10 08:15:00 UTC (1510301700)
> kworker/0:1-67    [000] .... 145.156235: rtc_timer_fired: RTC timer:(ffffffc15ad913c8) 2017-11-10 08:15:00 UTC (1510301700)
> kworker/0:1-67    [000] .... 145.173137: rtc_set_alarm: 2017-11-10 08:17:00 UTC (1510301820)
> 
> the second alarm timer was expired:
> kworker/0:1-67    [000] .... 269.102985: rtc_timer_dequeue: RTC timer:(ffffff80088e6430) 2017-11-10 08:17:00 UTC (1510301820)
> kworker/0:1-67    [000] .... 269.102992: rtc_timer_fired: RTC timer:(ffffff80088e6430) 2017-11-10 08:17:00 UTC (1510301820)
> 
> disable alarm irq:
> kworker/0:1-67    [000] .... 269.103098: rtc_alarm_irq_enable: disable RTC alarm IRQ
> 
> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
> ---
>  drivers/rtc/interface.c    |   46 ++++++++++
>  include/trace/events/rtc.h |  215 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 261 insertions(+)
>  create mode 100644 include/trace/events/rtc.h
> 
> diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
> index 8cec9a0..cdd3ac8 100644
> --- a/drivers/rtc/interface.c
> +++ b/drivers/rtc/interface.c
> @@ -17,6 +17,9 @@
>  #include <linux/log2.h>
>  #include <linux/workqueue.h>
>  
> +#define CREATE_TRACE_POINTS
> +#include <trace/events/rtc.h>
> +
>  static int rtc_timer_enqueue(struct rtc_device *rtc, struct rtc_timer *timer);
>  static void rtc_timer_remove(struct rtc_device *rtc, struct rtc_timer *timer);
>  
> @@ -53,6 +56,9 @@ int rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm)
>  
>  	err = __rtc_read_time(rtc, tm);
>  	mutex_unlock(&rtc->ops_lock);
> +
> +	if (!err)
> +		trace_rtc_read_time(tm);

It's better to just add unconditional tracepoints and trace the failures as well - 
this makes things faster for the non-traced case, plus it's much easier to read as 
well.

I.e. something like:

	trace_rtc_read_time(tm, err);

etc.

> @@ -790,6 +818,8 @@ static int rtc_timer_enqueue(struct rtc_device *rtc, struct rtc_timer *timer)
>  			schedule_work(&rtc->irqwork);
>  		} else if (err) {
>  			timerqueue_del(&rtc->timerqueue, &timer->node);
> +			trace_rtc_timer_dequeue(timer,
> +					rtc_ktime_to_tm(timer->node.expires));

Please don't break the line in such an ugly fashion.

> @@ -803,6 +833,7 @@ static void rtc_alarm_disable(struct rtc_device *rtc)
>  		return;
>  
>  	rtc->ops->alarm_irq_enable(rtc->dev.parent, false);
> +	trace_rtc_alarm_irq_enable(0);

Since there's so many new events already, why not add an enable/disable variant 
instead of parameterizing the 'enable' event?

>  	timerqueue_del(&rtc->timerqueue, &timer->node);
> +	trace_rtc_timer_dequeue(timer, rtc_ktime_to_tm(timer->node.expires));

> +		trace_rtc_timer_dequeue(timer,
> +				rtc_ktime_to_tm(timer->node.expires));

> +		trace_rtc_timer_fired(timer,
> +				rtc_ktime_to_tm(timer->node.expires));

> +			trace_rtc_timer_enqueue(timer,
> +					rtc_ktime_to_tm(timer->node.expires));

All the decoding of expiry time should be done in the trace handler, don't bloat 
the call site with it.

Thanks,

	Ingo