[PATCH v5 3/9] fs: add percpu counters for significant multigrain timestamp events

Jeff Layton
2024-07-11T11:08:34Z

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@kernel.org>
---
fs/inode.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 59 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index 81b45e0a95a6..011148c82901 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 atomic64_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 (!atomic64_try_cmpxchg(&ctime_floor, &old, fine))
+ if (atomic64_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 = timestamp_truncate(ktime_to_timespec64(now), inode);
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