linux-kernel - [PATCH v4 3/9] fs: add percpu counters for significant multigrain timestamp events

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Message-Id: <20240708-mgtime-v4-3-a0f3c6fb57f3@kernel.org>
Date: Mon, 08 Jul 2024 11:53:36 -0400
From: Jeff Layton <jlayton@...nel.org>
To: 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>, 
 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>, 
 Jonathan Corbet <corbet@....net>
Cc: Dave Chinner <david@...morbit.com>, Andi Kleen <ak@...ux.intel.com>, 
 Christoph Hellwig <hch@...radead.org>, Uros Bizjak <ubizjak@...il.com>, 
 Kent Overstreet <kent.overstreet@...ux.dev>, kernel-team@...com, 
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-trace-kernel@...r.kernel.org, linux-xfs@...r.kernel.org, 
 linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-mm@...ck.org, 
 linux-nfs@...r.kernel.org, linux-doc@...r.kernel.org, 
 Jeff Layton <jlayton@...nel.org>
Subject: [PATCH v4 3/9] fs: add percpu counters for significant multigrain
 timestamp events

Four percpu counters for counting various stats around mgtimes, and a
new debugfs file for displaying them:

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

Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 fs/inode.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 59 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index b2ff309a400a..9b93d0a47e55 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>
@@ -70,6 +72,11 @@ static __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_hash_lock);
  */
 static __cacheline_aligned_in_smp ktime_t ctime_floor;
 
+static struct percpu_counter mg_ctime_updates;
+static struct percpu_counter mg_floor_swaps;
+static struct percpu_counter mg_ctime_swaps;
+static struct percpu_counter mg_fine_stamps;
+
 /*
  * Empty aops. Can be used for the cases where the user does not
  * define any of the address_space operations.
@@ -2654,6 +2661,7 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)
 
 			/* Get a fine-grained time */
 			fine = ktime_get();
+			percpu_counter_inc(&mg_fine_stamps);
 
 			/*
 			 * If the cmpxchg works, we take the new floor value. If
@@ -2662,11 +2670,14 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)
 			 * as good, so keep it.
 			 */
 			old = floor;
-			if (!try_cmpxchg(&ctime_floor, &old, fine))
+			if (try_cmpxchg(&ctime_floor, &old, fine))
+				percpu_counter_inc(&mg_floor_swaps);
+			else
 				fine = old;
 			now = ktime_mono_to_real(fine);
 		}
 	}
+	percpu_counter_inc(&mg_ctime_updates);
 	now_ts = ktime_to_timespec64(now);
 	cur = cns;
 retry:
@@ -2675,6 +2686,7 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)
 		/* If swap occurred, then we're (mostly) done */
 		inode->i_ctime_sec = now_ts.tv_sec;
 		trace_ctime_ns_xchg(inode, cns, now_ts.tv_nsec, cur);
+		percpu_counter_inc(&mg_ctime_swaps);
 	} else {
 		/*
 		 * Was the change due to someone marking the old ctime QUERIED?
@@ -2744,3 +2756,49 @@ umode_t mode_strip_sgid(struct mnt_idmap *idmap,
 	return mode & ~S_ISGID;
 }
 EXPORT_SYMBOL(mode_strip_sgid);
+
+static int mgts_show(struct seq_file *s, void *p)
+{
+	u64 ctime_updates = percpu_counter_sum(&mg_ctime_updates);
+	u64 ctime_swaps = percpu_counter_sum(&mg_ctime_swaps);
+	u64 fine_stamps = percpu_counter_sum(&mg_fine_stamps);
+	u64 floor_swaps = percpu_counter_sum(&mg_floor_swaps);
+
+	seq_printf(s, "%llu %llu %llu %llu\n",
+		   ctime_updates, ctime_swaps, fine_stamps, floor_swaps);
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(mgts);
+
+static int __init mg_debugfs_init(void)
+{
+	int ret = percpu_counter_init(&mg_ctime_updates, 0, GFP_KERNEL);
+
+	if (ret)
+		return ret;
+
+	ret = percpu_counter_init(&mg_floor_swaps, 0, GFP_KERNEL);
+	if (ret) {
+		percpu_counter_destroy(&mg_ctime_updates);
+		return ret;
+	}
+
+	ret = percpu_counter_init(&mg_ctime_swaps, 0, GFP_KERNEL);
+	if (ret) {
+		percpu_counter_destroy(&mg_floor_swaps);
+		percpu_counter_destroy(&mg_ctime_updates);
+		return ret;
+	}
+
+	ret = percpu_counter_init(&mg_fine_stamps, 0, GFP_KERNEL);
+	if (ret) {
+		percpu_counter_destroy(&mg_floor_swaps);
+		percpu_counter_destroy(&mg_ctime_updates);
+		percpu_counter_destroy(&mg_ctime_swaps);
+		return ret;
+	}
+	debugfs_create_file("multigrain_timestamps", S_IFREG | S_IRUGO, NULL, NULL, &mgts_fops);
+	return 0;
+}
+late_initcall(mg_debugfs_init);

-- 
2.45.2