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Date: Thu, 8 Sep 2016 15:56:58 +0900
From: Masami Hiramatsu <masami.hiramatsu@...aro.org>
To: Binoy Jayan <binoy.jayan@...aro.org>
Cc: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
Daniel Wagner <daniel.wagner@...-carit.de>,
Arnd Bergmann <arnd@...db.de>,
Linux kernel mailing list <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v6 4/4] tracing: Histogram for delayed hrtimer offsets
2016-09-07 20:13 GMT+09:00 Binoy Jayan <binoy.jayan@...aro.org>:
> 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@...aro.org>
> ---
> 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
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