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Date: Fri, 2 Sep 2016 09:20:18 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Binoy Jayan <binoy.jayan@...aro.org>
Cc: Ingo Molnar <mingo@...hat.com>,
Daniel Wagner <daniel.wagner@...-carit.de>,
Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
Masami <masami.hiramatsu@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v5 4/4] tracing: Histogram for delayed hrtimer offsets
[ Added Cc to hrtimer maintainer ]
On Fri, 2 Sep 2016 18:07:31 +0530
Binoy Jayan <binoy.jayan@...aro.org> wrote:
> 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=common_pid.execname,tcomm'
>
> Signed-off-by: Binoy Jayan <binoy.jayan@...aro.org>
> ---
> include/linux/hrtimer.h | 3 +++
> include/trace/events/latency.h | 23 +++++++++++++++++++++
> kernel/time/hrtimer.c | 46 ++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 72 insertions(+)
>
> diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
> index 5e00f80..e09de14 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;
> +#if defined(CONFIG_PREEMPT_TRACER) || defined(CONFIG_IRQSOFF_TRACER)
> + ktime_t praecox;
> +#endif
> #ifdef CONFIG_TIMER_STATS
> int start_pid;
> void *start_site;
> diff --git a/include/trace/events/latency.h b/include/trace/events/latency.h
> index ca57f06..d616db5 100644
> --- a/include/trace/events/latency.h
> +++ b/include/trace/events/latency.h
> @@ -44,6 +44,29 @@ DEFINE_EVENT(latency_template, latency_preempt,
> TP_PROTO(int ltype, cycles_t latency),
> TP_ARGS(ltype, latency));
>
> +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)
> +);
This probably should be added into the hrtimer interrupt tracepoints
and not off in some special tracepoint header.
> +
> #endif /* _TRACE_HIST_H */
>
> /* This part must be outside protection */
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index 9ba7c82..04d936b 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -53,9 +53,12 @@
> #include <asm/uaccess.h>
>
> #include <trace/events/timer.h>
> +#include <trace/events/latency.h>
>
> #include "tick-internal.h"
>
> +static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer);
> +
> /*
> * The timer bases:
> *
> @@ -960,6 +963,45 @@ static inline ktime_t hrtimer_update_lowres(struct hrtimer *timer, ktime_t tim,
> return tim;
> }
>
> +static inline void latency_hrtimer_timing_start(struct hrtimer *timer,
> + struct hrtimer_clock_base *new_base,
> + ktime_t tim)
> +{
> +#if defined(CONFIG_PREEMPT_TRACER) || defined(CONFIG_IRQSOFF_TRACER)
The ideal approach to #ifdefs like this, is not to add them in side
each function, as it is confusing to understand, but simply have one:
#if defined(CONFIG_PREEMPT_TRACER) || defined(CONFIG_IRQSOFF_TRACER)
static inline void latency_hrtimer_timing_start(..)
{
> + 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(..)
{
[...]
}
#else
static inline void latency_hrtimer_timing_start(..) { }
static inline void latency_hrtimer_timing_stop(..) { }
#endif
But something like this patch is going to need Thomas's approval.
-- Steve
> +#endif
> +}
> +
> +static inline void latency_hrtimer_timing_stop(struct hrtimer *timer,
> + ktime_t basenow)
> +{
> +#if defined(CONFIG_PREEMPT_TRACER) || defined(CONFIG_IRQSOFF_TRACER)
> + 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);
> +#endif
> +}
> +
> /**
> * hrtimer_start_range_ns - (re)start an hrtimer on the current CPU
> * @timer: the timer to be added
> @@ -992,6 +1034,8 @@ 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 +1328,8 @@ 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
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