[PATCH v10 02/12] timekeeping: add percpu counter for tracking floor swap events

[Jeff Layton <jlayton@xxxxxxxxxx>]

The mgtime_floor value is a global variable for tracking the latest
fine-grained timestamp handed out. Because it's a global, track the
number of times that a new floor value is assigned.

Add a new percpu counter to the timekeeping code to track the number of
floor swap events that have occurred. A later patch will add a debugfs
file to display this counter alongside other stats involving multigrain
timestamps.

Tested-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> # documentation bits
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 include/linux/timekeeping.h        |  1 +
 kernel/time/timekeeping.c          |  1 +
 kernel/time/timekeeping_debug.c    | 14 ++++++++++++++
 kernel/time/timekeeping_internal.h | 15 +++++++++++++++
 4 files changed, 31 insertions(+)

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 7aa85246c183576b039c02af4abba02b4a09ef9d..84a035e86ac811f9e7b1649246b71c9296519149 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -48,6 +48,7 @@ extern void ktime_get_coarse_real_ts64(struct timespec64 *ts);
 /* Multigrain timestamp interfaces */
 extern void ktime_get_coarse_real_ts64_mg(struct timespec64 *ts);
 extern void ktime_get_real_ts64_mg(struct timespec64 *ts);
+extern unsigned long timekeeping_get_mg_floor_swaps(void);
 
 void getboottime64(struct timespec64 *ts);
 
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index ebfe846ebde35850c3e4d9c2cc45642c983d137f..e8b713e8ce5553f9e7de96c8e7c089714e0aa7a4 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -2488,6 +2488,7 @@ void ktime_get_real_ts64_mg(struct timespec64 *ts)
 	if (atomic64_try_cmpxchg(&mg_floor, &old, mono)) {
 		ts->tv_nsec = 0;
 		timespec64_add_ns(ts, nsecs);
+		timekeeping_inc_mg_floor_swaps();
 	} else {
 		/*
 		 * Another task changed mg_floor since "old" was fetched.
diff --git a/kernel/time/timekeeping_debug.c b/kernel/time/timekeeping_debug.c
index b73e8850e58d9c5b291559f475e67c7ed47c2db3..36d359cad7ca1d821bf42f59b3e50f89b14afd40 100644
--- a/kernel/time/timekeeping_debug.c
+++ b/kernel/time/timekeeping_debug.c
@@ -17,6 +17,9 @@
 
 #define NUM_BINS 32
 
+/* incremented every time mg_floor is updated */
+DEFINE_PER_CPU(unsigned long, timekeeping_mg_floor_swaps);
+
 static unsigned int sleep_time_bin[NUM_BINS] = {0};
 
 static int tk_debug_sleep_time_show(struct seq_file *s, void *data)
@@ -53,3 +56,14 @@ void tk_debug_account_sleep_time(const struct timespec64 *t)
 			   (s64)t->tv_sec, t->tv_nsec / NSEC_PER_MSEC);
 }
 
+unsigned long timekeeping_get_mg_floor_swaps(void)
+{
+	unsigned long sum = 0;
+	int cpu;
+
+	for_each_possible_cpu(cpu)
+		sum += data_race(per_cpu(timekeeping_mg_floor_swaps, cpu));
+
+	return sum;
+}
+
diff --git a/kernel/time/timekeeping_internal.h b/kernel/time/timekeeping_internal.h
index 4ca2787d1642e2f52bf985607ca3b03785cf9a50..0bbae825bc0226e4eed64e73fe3b454986c7573f 100644
--- a/kernel/time/timekeeping_internal.h
+++ b/kernel/time/timekeeping_internal.h
@@ -10,9 +10,24 @@
  * timekeeping debug functions
  */
 #ifdef CONFIG_DEBUG_FS
+
+DECLARE_PER_CPU(unsigned long, timekeeping_mg_floor_swaps);
+
+static inline void timekeeping_inc_mg_floor_swaps(void)
+{
+	this_cpu_inc(timekeeping_mg_floor_swaps);
+}
+
 extern void tk_debug_account_sleep_time(const struct timespec64 *t);
+
 #else
+
 #define tk_debug_account_sleep_time(x)
+
+static inline void timekeeping_inc_mg_floor_swaps(void)
+{
+}
+
 #endif
 
 #ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE

-- 
2.46.2