linux-kernel - Re: [PATCH 1/6] trace: add tracepoints to timekeeping code

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Message-ID: <20110617141913.GF25197@somewhere.redhat.com>
Date:	Fri, 17 Jun 2011 16:19:15 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	David Ahern <dsahern@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	acme@...stprotocols.net, mingo@...e.hu, paulus@...ba.org,
	johnstul@...ibm.com, rostedt@...dmis.org
Subject: Re: [PATCH 1/6] trace: add tracepoints to timekeeping code - xtime
 changes

On Fri, Jun 17, 2011 at 08:13:19AM -0600, David Ahern wrote:
> 
> 
> On 06/17/2011 07:23 AM, Frederic Weisbecker wrote:
> > 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@...il.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?
> 
> This use case only cares that xtime is updated.
> 
> > 
> > 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.
> 
> Peter and Thomas expressed interest in timekeeping tracepoints. How the
> update happens might be wanted. If desired I can consolidate xtime = *tv
> into a single update function and put the trace point there.

Peter, Thomas, any opinion about that?
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