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

Jeff Layton
2024-10-02T18:50:09Z

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@toxicpanda.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Tested-by: Randy Dunlap <rdunlap@infradead.org> # documentation bits
Signed-off-by: Jeff Layton <jlayton@kernel.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