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

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Date:   Wed, 15 Nov 2017 17:57:16 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, linux-rtc@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] rtc: Add tracepoints for RTC system

Hi Ingo,

On 15 November 2017 at 16:35, Ingo Molnar <mingo@...nel.org> wrote:
>
> * 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);

Yes, that's will be better.

>
> 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.

I will try to modify it in next version.

>
>> @@ -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?

Since the rtc_alarm_irq_enable() is one separate function and can be
called from userspace individually.

>
>>       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.

OK. Thanks for your comments.

-- 
Baolin.wang
Best Regards