linux-kernel - [PATCH 05/10] fs: add percpu counters to count fine vs. coarse timestamps

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Date: Wed, 26 Jun 2024 21:00:25 -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>
Cc: 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, 
 Jeff Layton <jlayton@...nel.org>
Subject: [PATCH 05/10] fs: add percpu counters to count fine vs. coarse
 timestamps

Keep a pair of percpu counters so we can track what proportion of
timestamps is fine-grained.

Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 fs/inode.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/fs/inode.c b/fs/inode.c
index 12790a26102c..18a9d1398773 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>
@@ -64,6 +66,11 @@ static __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_hash_lock);

 /* Don't send out a ctime lower than this (modulo backward clock jumps). */
 static __cacheline_aligned_in_smp ktime_t ctime_floor;
+
+/* Keep track of the number of fine vs. coarse timestamp fetches */
+static struct percpu_counter mg_fine_ts;
+static struct percpu_counter mg_coarse_ts;
+
 /*
  * Empty aops. Can be used for the cases where the user does not
  * define any of the address_space operations.
@@ -2636,6 +2643,9 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)
 		trace_ctime_floor_update(inode, floor, now, old);
 		if (old != floor)
 			now = old;
+		percpu_counter_inc(&mg_fine_ts);
+	} else {
+		percpu_counter_inc(&mg_coarse_ts);
 	}
 retry:
 	/* Try to swap the ctime into place. */
@@ -2711,3 +2721,32 @@ 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 fine = percpu_counter_sum(&mg_fine_ts);
+	u64 coarse = percpu_counter_sum(&mg_coarse_ts);
+
+	seq_printf(s, "%llu %llu\n", fine, coarse);
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(mgts);
+
+static int __init mg_debugfs_init(void)
+{
+	int ret = percpu_counter_init(&mg_fine_ts, 0, GFP_KERNEL);
+
+	if (ret)
+		return ret;
+
+	ret = percpu_counter_init(&mg_coarse_ts, 0, GFP_KERNEL);
+	if (ret) {
+		percpu_counter_destroy(&mg_fine_ts);
+		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