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
- number of floor value swap events

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>
Link: https://lore.kernel.org/r/20241002-mgtime-v10-7-d1c4717f5284@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/inode.c b/fs/inode.c
index f7a25c511d6b7069fa235135cf3bad0cda32815b..6d501c7308aefcbb8001d64cb46e57f1839b8a3b 100644 (file)
--- 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 +103,70 @@ 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)
+{
+       unsigned long sum = 0;
+       int i;
+
+       for_each_possible_cpu(i)
+               sum += data_race(per_cpu(mg_ctime_updates, i));
+       return sum;
+}
+
+static unsigned long get_mg_fine_stamps(void)
+{
+       unsigned long sum = 0;
+       int i;
+
+       for_each_possible_cpu(i)
+               sum += data_race(per_cpu(mg_fine_stamps, i));
+       return sum;
+}
+
+static unsigned long get_mg_ctime_swaps(void)
+{
+       unsigned long sum = 0;
+       int i;
+
+       for_each_possible_cpu(i)
+               sum += data_race(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();
+       unsigned long floor_swaps = timekeeping_get_mg_floor_swaps();
+
+       seq_printf(s, "%lu %lu %lu %lu\n",
+                  ctime_updates, ctime_swaps, fine_stamps, floor_swaps);
+       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 +2755,10 @@ 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 +2772,7 @@ retry:
                /* 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?