linux-kernel - Re: [PATCH v3] rtc: Add tracepoints for RTC system

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Date:   Thu, 14 Dec 2017 12:49:12 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     a.zummo@...ertech.it, alexandre.belloni@...e-electrons.com,
        mingo@...hat.com, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org, arnd@...db.de, broonie@...nel.org
Subject: Re: [PATCH v3] rtc: Add tracepoints for RTC system

On Thu, 14 Dec 2017 13:31:43 +0800
Baolin Wang <baolin.wang@...aro.org> wrote:


> @@ -53,6 +56,8 @@ int rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm)
>  
>  	err = __rtc_read_time(rtc, tm);
>  	mutex_unlock(&rtc->ops_lock);
> +
> +	trace_rtc_read_time(rtc_tm_to_time64(tm), err);

There's a possibility that gcc may put the call to rt_tm_to_time64()
outside the tracepoint area that gets nop'd out. Could you just pass in
the tm to the tracepoint, and have the call to rtc_tm_to_time64() done
within the TP_fast_assign? This would guarantee that we don't incur
overhead when tracing is off.

	TP_PROTO(struct rtc_time *tm, int err),

	TP_ARGS(tm, err),

	TP_fast_assign(
		__entry->secs = rt_tm_to_time64(tm);

-- Steve


> diff --git a/include/trace/events/rtc.h b/include/trace/events/rtc.h
> new file mode 100644
> index 0000000..621333f
> --- /dev/null
> +++ b/include/trace/events/rtc.h
> @@ -0,0 +1,206 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM rtc
> +
> +#if !defined(_TRACE_RTC_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_RTC_H
> +
> +#include <linux/rtc.h>
> +#include <linux/tracepoint.h>
> +
> +DECLARE_EVENT_CLASS(rtc_time_alarm_class,
> +
> +	TP_PROTO(time64_t secs, int err),
> +
> +	TP_ARGS(secs, err),
> +
> +	TP_STRUCT__entry(
> +		__field(time64_t, secs)
> +		__field(int, err)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->secs = secs;
> +		__entry->err = err;
> +	),
> +
> +	TP_printk("UTC (%lld) (%d)",
> +		  __entry->secs, __entry->err
> +	)
> +);
> +
> +DEFINE_EVENT(rtc_time_alarm_class, rtc_set_time,
> +
> +	TP_PROTO(time64_t secs, int err),
> +
> +	TP_ARGS(secs, err)
> +);
> +
> +DEFINE_EVENT(rtc_time_alarm_class, rtc_read_time,
> +
> +	TP_PROTO(time64_t secs, int err),
> +
> +	TP_ARGS(secs, err)
> +);
> +