linux-kernel - [PATCH v9 07/12] timekeeping: add percpu counter for tracking floor swap events

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Message-Id: <20241002-mgtime-v9-7-77e2baad57ac@kernel.org>
Date: Wed, 02 Oct 2024 14:49:35 -0400
From: Jeff Layton <jlayton@...nel.org>
To: John Stultz <jstultz@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, 
 Stephen Boyd <sboyd@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
 Steven Rostedt <rostedt@...dmis.org>, 
 Masami Hiramatsu <mhiramat@...nel.org>, 
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
 Jonathan Corbet <corbet@....net>, Randy Dunlap <rdunlap@...radead.org>, 
 Chandan Babu R <chandan.babu@...cle.com>, 
 "Darrick J. Wong" <djwong@...nel.org>, Theodore Ts'o <tytso@....edu>, 
 Andreas Dilger <adilger.kernel@...ger.ca>, Chris Mason <clm@...com>, 
 Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>, 
 Hugh Dickins <hughd@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
 Chuck Lever <chuck.lever@...cle.com>, 
 Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
 linux-trace-kernel@...r.kernel.org, linux-doc@...r.kernel.org, 
 linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org, 
 linux-btrfs@...r.kernel.org, linux-nfs@...r.kernel.org, linux-mm@...ck.org, 
 Jeff Layton <jlayton@...nel.org>
Subject: [PATCH v9 07/12] timekeeping: add percpu counter for tracking
 floor swap events

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@...radead.org> # documentation bits
Signed-off-by: Jeff Layton <jlayton@...nel.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 0223f8ec3cfb..1edac9ab1ecc 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 ebfe846ebde3..e8b713e8ce55 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 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