Re: [PATCH v6 4/4] tracing: Histogram for delayed hrtimer offsets

[Masami Hiramatsu]

2016-09-07 20:13 GMT+09:00 Binoy Jayan <binoy.jayan@xxxxxxxxxx>:
> Generate a histogram of the latencies of delayed timer offsets in
> nanoseconds. It shows the latency captured due to a delayed timer expire
> event. It happens for example when a timer misses its deadline due to
> disabled interrupts. A process if scheduled as a result of the timer
> expiration suffers this latency.
>
> The following filter(s) may be used
>
> 'hist:key=common_pid.execname:val=toffset,hitcount'
> 'hist:key=cpu,tcomm:val=toffset:sort=tcomm'
> 'hist:key=comm,tcomm:sort=comm,tcomm'
>

Ok, so this event is hit only when the hrtimer is delayed.

I just have a comment on the event name:

> +TRACE_EVENT(latency_hrtimer_interrupt,

Since this event will be hit only when the hrtimer is delayed,
would we better add "delayed" in the event name?
e.g. "latency_delayed_hrtimer"

Others are OK for me.

Thanks,

> Signed-off-by: Binoy Jayan <binoy.jayan@xxxxxxxxxx>
> ---
>  include/linux/hrtimer.h      |  3 +++
>  include/trace/events/timer.h | 25 +++++++++++++++++++++
>  kernel/time/Kconfig          |  7 ++++++
>  kernel/time/hrtimer.c        | 52 ++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 87 insertions(+)
>
> diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
> index 5e00f80..9146842 100644
> --- a/include/linux/hrtimer.h
> +++ b/include/linux/hrtimer.h
> @@ -104,6 +104,9 @@ struct hrtimer {
>         struct hrtimer_clock_base       *base;
>         u8                              state;
>         u8                              is_rel;
> +#ifdef CONFIG_DELAYED_TIMER_OFFSETS_HIST
> +       ktime_t                         praecox;
> +#endif
>  #ifdef CONFIG_TIMER_STATS
>         int                             start_pid;
>         void                            *start_site;
> diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
> index 28c5da6..ee45aed 100644
> --- a/include/trace/events/timer.h
> +++ b/include/trace/events/timer.h
> @@ -382,6 +382,31 @@ TRACE_EVENT(tick_stop,
>  );
>  #endif
>
> +#ifdef CONFIG_DELAYED_TIMER_OFFSETS_HIST
> +TRACE_EVENT(latency_hrtimer_interrupt,
> +
> +       TP_PROTO(long long toffset, struct task_struct *task),
> +
> +       TP_ARGS(toffset, task),
> +
> +       TP_STRUCT__entry(
> +               __field(long long,      toffset)
> +               __array(char,           tcomm,  TASK_COMM_LEN)
> +               __field(int,            tprio)
> +       ),
> +
> +       TP_fast_assign(
> +               __entry->toffset = toffset;
> +               memcpy(__entry->tcomm, task != NULL ? task->comm : "<none>",
> +                       task != NULL ? TASK_COMM_LEN : 7);
> +               __entry->tprio  = task != NULL ? task->prio : -1;
> +       ),
> +
> +       TP_printk("toffset=%lld thread=%s[%d]",
> +               __entry->toffset, __entry->tcomm, __entry->tprio)
> +);
> +#endif
> +
>  #endif /*  _TRACE_TIMER_H */
>
>  /* This part must be outside protection */
> diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
> index 4008d9f..8ff19dd 100644
> --- a/kernel/time/Kconfig
> +++ b/kernel/time/Kconfig
> @@ -193,5 +193,12 @@ config HIGH_RES_TIMERS
>           hardware is not capable then this option only increases
>           the size of the kernel image.
>
> +config DELAYED_TIMER_OFFSETS_HIST
> +       depends on HIGH_RES_TIMERS
> +       select GENERIC_TRACER
> +       bool "Delayed Timer Offsets Histogram"
> +       help
> +         Generate a histogram of delayed timer offsets in nanoseconds.
> +
>  endmenu
>  endif
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index 9ba7c82..432d49a 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -56,6 +56,8 @@
>
>  #include "tick-internal.h"
>
> +static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer);
> +
>  /*
>   * The timer bases:
>   *
> @@ -960,6 +962,52 @@ static inline ktime_t hrtimer_update_lowres(struct hrtimer *timer, ktime_t tim,
>         return tim;
>  }
>
> +#ifdef CONFIG_DELAYED_TIMER_OFFSETS_HIST
> +static inline void latency_hrtimer_timing_start(struct hrtimer *timer,
> +                                        struct hrtimer_clock_base *new_base,
> +                                        ktime_t tim)
> +{
> +       if (unlikely(trace_latency_hrtimer_interrupt_enabled())) {
> +               ktime_t now = new_base->get_time();
> +
> +               if (ktime_to_ns(tim) < ktime_to_ns(now))
> +                       timer->praecox = now;
> +               else
> +                       timer->praecox = ktime_set(0, 0);
> +       }
> +}
> +
> +static inline void latency_hrtimer_timing_stop(struct hrtimer *timer,
> +                                               ktime_t basenow)
> +{
> +       long latency;
> +       struct task_struct *task;
> +
> +       if (likely(!trace_latency_hrtimer_interrupt_enabled()))
> +               return;
> +
> +       latency = ktime_to_ns(ktime_sub(basenow,
> +                             ktime_to_ns(timer->praecox) ?
> +                             timer->praecox : hrtimer_get_expires(timer)));
> +       task = timer->function == hrtimer_wakeup ?
> +                       container_of(timer, struct hrtimer_sleeper,
> +                                    timer)->task : NULL;
> +       if (latency > 0)
> +               trace_latency_hrtimer_interrupt((u64) latency, task);
> +}
> +#else
> +static inline void latency_hrtimer_timing_start(struct hrtimer *timer,
> +                                        struct hrtimer_clock_base *new_base,
> +                                        ktime_t tim)
> +{
> +}
> +static inline void latency_hrtimer_timing_stop(struct hrtimer *timer,
> +                                               ktime_t basenow)
> +{
> +}
> +
> +#endif
> +
>  /**
>   * hrtimer_start_range_ns - (re)start an hrtimer on the current CPU
>   * @timer:     the timer to be added
> @@ -992,6 +1040,8 @@ void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
>
>         timer_stats_hrtimer_set_start_info(timer);
>
> +       latency_hrtimer_timing_start(timer, new_base, tim);
> +
>         leftmost = enqueue_hrtimer(timer, new_base);
>         if (!leftmost)
>                 goto unlock;
> @@ -1284,6 +1334,8 @@ static void __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now)
>
>                         timer = container_of(node, struct hrtimer, node);
>
> +                       latency_hrtimer_timing_stop(timer, basenow);
> +
>                         /*
>                          * The immediate goal for using the softexpires is
>                          * minimizing wakeups, not running timers at the
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>



-- 
Masami Hiramatsu