[PATCH] hrtimer: CPU and entry_time is added to a warning message in hrtimer_interrupt()

[Rei Yamamoto]

A warning message in hrtimer_interrupt() is output up to 5 times
by default, and CPU and entry_time are also shown.
These changes are helpful that the function spending a lot of time is clear
by using ftrace:
-----
dmesg
:
[ 1462.836971] start repro_hrtimer_interrupt
[ 1462.836976] test_handler = test_handler [repro] 0xffff9788f7bb3048
:
[ 1462.879117] hrtimer: CPU 7, entry_time = 1462807264840, interrupt took
60048886 ns             ^^^^^               ^^^^^^^^^^^^^

cat /sys/kernel/debug/tracing/trace
:
          <idle>-0       [007] d.h1.  1462.838075: hrtimer_expire_entry:
                         ^^^^^
hrtimer=0000000041fcee42 function=test_handler [repro] now=1462807264840
                                                           ^^^^^^^^^^^^^
-----

Signed-off-by: Rei Yamamoto <yamamoto.rei@xxxxxxxxxxxxxx>
---
 include/linux/hrtimer.h |  1 +
 kernel/sysctl.c         | 10 ++++++++++
 kernel/time/hrtimer.c   | 16 +++++++++++++++-
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 0ee140176f10..1a6e03b3015b 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -317,6 +317,7 @@ static inline int hrtimer_is_hres_active(struct hrtimer *timer)
 struct clock_event_device;
 
 extern void hrtimer_interrupt(struct clock_event_device *dev);
+extern int sysctl_hrtimer_interrupt_warnings;
 
 extern unsigned int hrtimer_resolution;
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e52b6e372c60..b0420d60cec9 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -64,6 +64,7 @@
 #include <linux/mount.h>
 #include <linux/userfaultfd_k.h>
 #include <linux/pid.h>
+#include <linux/hrtimer.h>
 
 #include "../lib/kstrtox.h"
 
@@ -2038,6 +2039,15 @@ static struct ctl_table kern_table[] = {
 		.extra1		= SYSCTL_ONE,
 		.extra2		= SYSCTL_INT_MAX,
 	},
+#endif
+#ifdef CONFIG_HIGH_RES_TIMERS
+	{
+		.procname       = "hrtimer_interrupt_warnings",
+		.data           = &sysctl_hrtimer_interrupt_warnings,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
 #endif
 	{ }
 };
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 0ea8702eb516..19adcbcf92e4 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1773,6 +1773,7 @@ static __latent_entropy void hrtimer_run_softirq(struct softirq_action *h)
 }
 
 #ifdef CONFIG_HIGH_RES_TIMERS
+int sysctl_hrtimer_interrupt_warnings = 5;
 
 /*
  * High resolution timer interrupt
@@ -1866,7 +1867,20 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 	else
 		expires_next = ktime_add(now, delta);
 	tick_program_event(expires_next, 1);
-	pr_warn_once("hrtimer: interrupt took %llu ns\n", ktime_to_ns(delta));
+
+	/*
+	 * If a message is output many times, the delayed funciton
+	 * may be identified by resetting sysctl_hrtimer_interrupt_warnings
+	 * and enabling ftrace.
+	 */
+	if (sysctl_hrtimer_interrupt_warnings) {
+		if (sysctl_hrtimer_interrupt_warnings > 0)
+			sysctl_hrtimer_interrupt_warnings--;
+		pr_warn("hrtimer: CPU %d, entry_time = %llu, "
+				"interrupt took %llu ns\n",
+				cpu_base->cpu, entry_time,
+				ktime_to_ns(delta));
+	}
 }
 
 /* called with interrupts disabled */
-- 
2.27.0