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Date: Fri, 17 Jun 2011 15:23:31 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: David Ahern <dsahern@gmail.com>
Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        acme@ghostprotocols.net, mingo@elte.hu, peterz@infradead.org,
        paulus@samba.org, tglx@linutronix.de, johnstul@us.ibm.com,
        rostedt@goodmis.org
Subject: Re: [PATCH 1/6] trace: add tracepoints to timekeeping code - xtime
 changes
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On Tue, Jun 07, 2011 at 05:55:03PM -0600, David Ahern wrote:
> Trace points in timekeeping.c where xtime is modified by a user
> or ntp.
> 
> Signed-off-by: David Ahern <dsahern@gmail.com>
> ---
>  include/trace/events/timekeeping.h |   43 ++++++++++++++++++++++++++++++++++++
>  kernel/time/timekeeping.c          |    8 ++++++
>  2 files changed, 51 insertions(+), 0 deletions(-)
>  create mode 100644 include/trace/events/timekeeping.h
> 
> diff --git a/include/trace/events/timekeeping.h b/include/trace/events/timekeeping.h
> new file mode 100644
> index 0000000..3d5d083
> --- /dev/null
> +++ b/include/trace/events/timekeeping.h
> @@ -0,0 +1,43 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM timekeeping
> +
> +#if !defined(_TRACE_TIMEKEEP_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_TIMEKEEP_H
> +
> +#include <linux/tracepoint.h>
> +#include <linux/time.h>
> +
> +DECLARE_EVENT_CLASS(tod_template,
> +
> +	TP_PROTO(const struct timespec *tv),
> +
> +	TP_ARGS(tv),
> +
> +	TP_STRUCT__entry(
> +		__field( __kernel_time_t,	tv_sec)
> +		__field( long,			tv_nsec)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->tv_sec  = tv->tv_sec;
> +		__entry->tv_nsec = tv->tv_nsec;
> +	),
> +
> +	TP_printk("tv_sec=%ld tv_nsec=%ld", __entry->tv_sec, __entry->tv_nsec)
> +);
> +
> +DEFINE_EVENT(tod_template, settimeofday,
> +	TP_PROTO(const struct timespec *tv),
> +	TP_ARGS(tv));
> +
> +DEFINE_EVENT(tod_template, timekeeping_inject_offset,
> +	TP_PROTO(const struct timespec *tv),
> +	TP_ARGS(tv));
> +
> +DEFINE_EVENT(tod_template, timekeeping_inject_sleeptime,
> +	TP_PROTO(const struct timespec *tv),
> +	TP_ARGS(tv));

Does the fact it's any of the three way of updating xtime make any
difference from the user point of view?

If not can we rather factorize that in a single settimeofday tracepoint?
Or update_time_of_day if we don't want to confuse the user with the
syscall.