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. Display that as a fourth integer
in /sys/kernel/debug/multigrain_timestamps.

Tested-by: Randy Dunlap <rdunlap@infradead.org> # documentation bits
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/inode.c                         |  5 +++--
 include/linux/timekeeping.h        |  1 +
 kernel/time/timekeeping.c          |  1 +
 kernel/time/timekeeping_debug.c    | 13 +++++++++++++
 kernel/time/timekeeping_internal.h |  9 +++++++++
 5 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index e46f7170851b..93a9365cc22d 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -145,9 +145,10 @@ static int mgts_show(struct seq_file *s, void *p)
 	unsigned long ctime_updates = get_mg_ctime_updates();
 	unsigned long ctime_swaps = get_mg_ctime_swaps();
 	unsigned long fine_stamps = get_mg_fine_stamps();
+	unsigned long floor_swaps = timekeeping_get_mg_floor_swaps();
 
-	seq_printf(s, "%lu %lu %lu\n",
-		   ctime_updates, ctime_swaps, fine_stamps);
+	seq_printf(s, "%lu %lu %lu %lu\n",
+		   ctime_updates, ctime_swaps, fine_stamps, floor_swaps);
 	return 0;
 }
 
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 7aa85246c183..84a035e86ac8 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 37004a4758cf..c8a934c1c8aa 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -2478,6 +2478,7 @@ 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 {
 		/*
 		 * Something has changed mg_floor since "old" was
diff --git a/kernel/time/timekeeping_debug.c b/kernel/time/timekeeping_debug.c
index b73e8850e58d..b731621ad811 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 +56,13 @@ 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)
+{
+	int i;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(i)
+		sum += per_cpu(timekeeping_mg_floor_swaps, i);
+	return sum < 0 ? 0 : sum;
+}
+
diff --git a/kernel/time/timekeeping_internal.h b/kernel/time/timekeeping_internal.h
index 4ca2787d1642..f53e76d5ee7c 100644
--- a/kernel/time/timekeeping_internal.h
+++ b/kernel/time/timekeeping_internal.h
@@ -10,9 +10,18 @@
  * 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