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Date: Tue, 20 Sep 2016 19:21:56 +0530
From: Binoy Jayan <binoy.jayan@...aro.org>
To: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>
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>,
Mark Brown <mark.brown@...aro.org>,
Binoy Jayan <binoy.jayan@...aro.org>,
Carsten Emde <C.Emde@...dl.org>
Subject: [RFC PATCH v7 4/5] tracing: Measure delayed hrtimer offset latency
Measure latencies caused due to 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. It is used to calculate the total wakeup latency
of a process which is the sum of the delayed timer offset and the
wakeup latency.
[
Initial work and idea by Carsten
Link: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit/?h=v3.14-rt-rebase&id=56d50cc34943bbba12b8c5942ee1ae3b29f73acb
]
Cc: Carsten Emde <C.Emde@...dl.org>
Signed-off-by: Binoy Jayan <binoy.jayan@...aro.org>
---
include/linux/hrtimer.h | 4 ++++
include/linux/sched.h | 3 +++
kernel/time/Kconfig | 8 ++++++++
kernel/time/hrtimer.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 62 insertions(+)
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 5e00f80..05d8086 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -90,6 +90,7 @@ enum hrtimer_restart {
* @is_rel: Set if the timer was armed relative
* @start_pid: timer statistics field to store the pid of the task which
* started the timer
+ * @tim_expiry: hrtimer expiry time or 0 in case already expired
* @start_site: timer statistics field to store the site where the timer
* was started
* @start_comm: timer statistics field to store the name of the process which
@@ -104,6 +105,9 @@ struct hrtimer {
struct hrtimer_clock_base *base;
u8 state;
u8 is_rel;
+#ifdef CONFIG_TRACE_DELAYED_TIMER_OFFSETS
+ ktime_t tim_expiry;
+#endif
#ifdef CONFIG_TIMER_STATS
int start_pid;
void *start_site;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 62c68e5..7bf67f8 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1891,6 +1891,9 @@ struct task_struct {
/* bitmask and counter of trace recursion */
unsigned long trace_recursion;
#endif /* CONFIG_TRACING */
+#ifdef CONFIG_TRACE_DELAYED_TIMER_OFFSETS
+ long timer_offset;
+#endif /* CONFIG_TRACE_DELAYED_TIMER_OFFSETS */
#ifdef CONFIG_KCOV
/* Coverage collection mode enabled for this task (0 if disabled). */
enum kcov_mode kcov_mode;
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 4008d9f..de4793c 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -193,5 +193,13 @@ config HIGH_RES_TIMERS
hardware is not capable then this option only increases
the size of the kernel image.
+config TRACE_DELAYED_TIMER_OFFSETS
+ depends on HIGH_RES_TIMERS
+ select GENERIC_TRACER
+ bool "Delayed Timer Offsets"
+ help
+ Capture offsets of delayed hrtimer in nanoseconds. It is used
+ to construct wakeup latency histogram.
+
endmenu
endif
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 9ba7c82..7048f86 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 +962,47 @@ static inline ktime_t hrtimer_update_lowres(struct hrtimer *timer, ktime_t tim,
return tim;
}
+#ifdef CONFIG_TRACE_DELAYED_TIMER_OFFSETS
+static inline void latency_hrtimer_timing_start(struct hrtimer *timer,
+ struct hrtimer_clock_base *new_base,
+ ktime_t tim)
+{
+ ktime_t now = new_base->get_time();
+
+ if (ktime_to_ns(tim) < ktime_to_ns(now))
+ timer->tim_expiry = now;
+ else
+ timer->tim_expiry = ktime_set(0, 0);
+}
+
+static inline void latency_hrtimer_timing_stop(struct hrtimer *timer,
+ ktime_t basenow)
+{
+ long latency;
+ struct task_struct *task;
+
+ latency = ktime_to_ns(ktime_sub(basenow,
+ ktime_to_ns(timer->tim_expiry) ?
+ timer->tim_expiry : hrtimer_get_expires(timer)));
+ task = timer->function == hrtimer_wakeup ?
+ container_of(timer, struct hrtimer_sleeper,
+ timer)->task : NULL;
+ if (task && latency > 0)
+ task->timer_offset = latency;
+}
+#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 +1035,8 @@ 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 +1329,8 @@ 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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