linux-kernel - [PATCH v9 06/12] fs: add percpu counters for significant multigrain timestamp events

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Message-Id: <20241002-mgtime-v9-6-77e2baad57ac@kernel.org>
Date: Wed, 02 Oct 2024 14:49:34 -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 06/12] fs: add percpu counters for significant
 multigrain timestamp events

New percpu counters for counting various stats around multigrain
timestamp events, and a new debugfs file for displaying them when
CONFIG_DEBUG_FS is enabled:

- number of attempted ctime updates
- number of successful i_ctime_nsec swaps
- number of fine-grained timestamp fetches

Reviewed-by: Josef Bacik <josef@...icpanda.com>
Reviewed-by: Darrick J. Wong <djwong@...nel.org>
Reviewed-by: Jan Kara <jack@...e.cz>
Tested-by: Randy Dunlap <rdunlap@...radead.org> # documentation bits
Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 fs/inode.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/fs/inode.c b/fs/inode.c
index f7a25c511d6b..0223f8ec3cfb 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -21,6 +21,8 @@
 #include <linux/list_lru.h>
 #include <linux/iversion.h>
 #include <linux/rw_hint.h>
+#include <linux/seq_file.h>
+#include <linux/debugfs.h>
 #include <trace/events/writeback.h>
 #define CREATE_TRACE_POINTS
 #include <trace/events/timestamp.h>
@@ -101,6 +103,69 @@ long get_nr_dirty_inodes(void)
 	return nr_dirty > 0 ? nr_dirty : 0;
 }
 
+#ifdef CONFIG_DEBUG_FS
+static DEFINE_PER_CPU(long, mg_ctime_updates);
+static DEFINE_PER_CPU(long, mg_fine_stamps);
+static DEFINE_PER_CPU(long, mg_ctime_swaps);
+
+static unsigned long get_mg_ctime_updates(void)
+{
+	int i;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(i)
+		sum += per_cpu(mg_ctime_updates, i);
+	return sum;
+}
+
+static unsigned long get_mg_fine_stamps(void)
+{
+	int i;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(i)
+		sum += per_cpu(mg_fine_stamps, i);
+	return sum;
+}
+
+static unsigned long get_mg_ctime_swaps(void)
+{
+	int i;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(i)
+		sum += per_cpu(mg_ctime_swaps, i);
+	return sum;
+}
+
+#define mgtime_counter_inc(__var)	this_cpu_inc(__var)
+
+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();
+
+	seq_printf(s, "%lu %lu %lu\n",
+		   ctime_updates, ctime_swaps, fine_stamps);
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(mgts);
+
+static int __init mg_debugfs_init(void)
+{
+	debugfs_create_file("multigrain_timestamps", S_IFREG | S_IRUGO, NULL, NULL, &mgts_fops);
+	return 0;
+}
+late_initcall(mg_debugfs_init);
+
+#else /* ! CONFIG_DEBUG_FS */
+
+#define mgtime_counter_inc(__var)	do { } while (0)
+
+#endif /* CONFIG_DEBUG_FS */
+
 /*
  * Handle nr_inode sysctl
  */
@@ -2689,8 +2754,10 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)
 		if (timespec64_compare(&now, &ctime) <= 0) {
 			ktime_get_real_ts64_mg(&now);
 			now = timestamp_truncate(now, inode);
+			mgtime_counter_inc(mg_fine_stamps);
 		}
 	}
+	mgtime_counter_inc(mg_ctime_updates);
 
 	/* No need to cmpxchg if it's exactly the same */
 	if (cns == now.tv_nsec && inode->i_ctime_sec == now.tv_sec) {
@@ -2704,6 +2771,7 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)
 		/* If swap occurred, then we're (mostly) done */
 		inode->i_ctime_sec = now.tv_sec;
 		trace_ctime_ns_xchg(inode, cns, now.tv_nsec, cur);
+		mgtime_counter_inc(mg_ctime_swaps);
 	} else {
 		/*
 		 * Was the change due to someone marking the old ctime QUERIED?

-- 
2.46.2