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    Subject[PATCH] ftrace: add tracepoint for xtime
    This patch can trace current xtime and wall_to_monotonic. Then user can
    use ctime() to convert them to wall time which is easier to be understood,
    especially for flight-recorder which need to get trace event from a kernel
    dump file.

    Example of ftrace output:
    <idle>-0 [000] 20118.489849: gtod_update_xtime: xtime=1243265589.999999824 wall_to_monotonic=3051713268.744158739
    <...>-4020 [001] 20118.489855: sys_open(filename: bf9e66e0, flags: 98800, mode: bf9e66e0)
    <...>-4020 [001] 20118.489873: sys_open -> 0xffffffec

    ctime(1243265590) = date:Mon May 25 11:33:10 2009
    So we can realize the task with pid 4020 open a file at
    Mon May 25 11:33:10 2009

    Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
    ---
    include/trace/events/xtime.h | 38 ++++++++++++++++++++++++++++++++++++++
    kernel/time/ntp.c | 2 ++
    kernel/time/timekeeping.c | 5 +++++
    3 files changed, 45 insertions(+), 0 deletions(-)
    create mode 100644 include/trace/events/xtime.h

    diff --git a/include/trace/events/xtime.h b/include/trace/events/xtime.h
    new file mode 100644
    index 0000000..f07bb64
    --- /dev/null
    +++ b/include/trace/events/xtime.h
    @@ -0,0 +1,38 @@
    +#if !defined(_TRACE_XTIME_H) || defined(TRACE_HEADER_MULTI_READ)
    +#define _TRACE_XTIME_H
    +
    +#include <linux/time.h>
    +#include <linux/tracepoint.h>
    +
    +#undef TRACE_SYSTEM
    +#define TRACE_SYSTEM xtime
    +
    +TRACE_EVENT(gtod_update_xtime,
    +
    + TP_PROTO(struct timespec *xtime, struct timespec *wall_to_monotonic),
    +
    + TP_ARGS(xtime, wall_to_monotonic),
    +
    + TP_STRUCT__entry(
    + __field( long, xtime_sec )
    + __field( long, xtime_nsec )
    + __field( long, wall_to_monotonic_sec )
    + __field( long, wall_to_monotonic_nsec )
    + ),
    +
    + TP_fast_assign(
    + __entry->xtime_sec = xtime->tv_sec;
    + __entry->xtime_nsec = xtime->tv_nsec;
    + __entry->wall_to_monotonic_sec = wall_to_monotonic->tv_sec;
    + __entry->wall_to_monotonic_nsec = wall_to_monotonic->tv_nsec;
    + ),
    +
    + TP_printk("xtime=%ld.%09ld wall_to_monotonic=%ld.%09ld",
    + __entry->xtime_sec, __entry->xtime_nsec,
    + __entry->wall_to_monotonic_sec, __entry->wall_to_monotonic_nsec)
    +);
    +
    +#endif /* _TRACE_XTIME_H */
    +
    +/* This part must be outside protection */
    +#include <trace/define_trace.h>
    diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
    index 7fc6437..33db762 100644
    --- a/kernel/time/ntp.c
    +++ b/kernel/time/ntp.c
    @@ -14,6 +14,7 @@
    #include <linux/timex.h>
    #include <linux/time.h>
    #include <linux/mm.h>
    +#include <trace/events/xtime.h>

    /*
    * NTP timekeeping variables:
    @@ -220,6 +221,7 @@ static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
    break;
    }
    update_vsyscall(&xtime, clock);
    + trace_gtod_update_xtime(&xtime, &wall_to_monotonic);

    write_sequnlock(&xtime_lock);

    diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
    index e8c77d9..798f93e 100644
    --- a/kernel/time/timekeeping.c
    +++ b/kernel/time/timekeeping.c
    @@ -19,6 +19,9 @@
    #include <linux/time.h>
    #include <linux/tick.h>

    +#define CREATE_TRACE_POINTS
    +#include <trace/events/xtime.h>
    +

    /*
    * This read-write spinlock protects us from races in SMP while
    @@ -171,6 +174,7 @@ int do_settimeofday(struct timespec *tv)
    ntp_clear();

    update_vsyscall(&xtime, clock);
    + trace_gtod_update_xtime(&xtime, &wall_to_monotonic);

    write_sequnlock_irqrestore(&xtime_lock, flags);

    @@ -568,6 +572,7 @@ void update_wall_time(void)
    /* check to see if there is a new clocksource to use */
    change_clocksource();
    update_vsyscall(&xtime, clock);
    + trace_gtod_update_xtime(&xtime, &wall_to_monotonic);
    }

    /**
    --
    1.6.1.2


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