[PATCH v6 3/9] fs: add percpu counters for significant multigrain timestamp events

[Jeff Layton]

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

Reviewed-by: Josef Bacik <jo...@toxicpanda.com>
Signed-off-by: Jeff Layton <jlay...@kernel.org>
---
 fs/inode.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 69 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index 869994285e87..fff844345c35 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>
@@ -80,6 +82,10 @@ EXPORT_SYMBOL(empty_aops);
 
 static DEFINE_PER_CPU(unsigned long, nr_inodes);
 static DEFINE_PER_CPU(unsigned long, nr_unused);
+static DEFINE_PER_CPU(unsigned long, mg_ctime_updates);
+static DEFINE_PER_CPU(unsigned long, mg_fine_stamps);
+static DEFINE_PER_CPU(unsigned long, mg_floor_swaps);
+static DEFINE_PER_CPU(unsigned long, mg_ctime_swaps);
 
 static struct kmem_cache *inode_cachep __ro_after_init;
 
@@ -101,6 +107,42 @@ static inline long get_nr_inodes_unused(void)
        return sum < 0 ? 0 : sum;
 }
 
+static long get_mg_ctime_updates(void)
+{
+       int i;
+       long sum = 0;
+       for_each_possible_cpu(i)
+               sum += per_cpu(mg_ctime_updates, i);
+       return sum < 0 ? 0 : sum;
+}
+
+static long get_mg_fine_stamps(void)
+{
+       int i;
+       long sum = 0;
+       for_each_possible_cpu(i)
+               sum += per_cpu(mg_fine_stamps, i);
+       return sum < 0 ? 0 : sum;
+}
+
+static long get_mg_floor_swaps(void)
+{
+       int i;
+       long sum = 0;
+       for_each_possible_cpu(i)
+               sum += per_cpu(mg_floor_swaps, i);
+       return sum < 0 ? 0 : sum;
+}
+
+static long get_mg_ctime_swaps(void)
+{
+       int i;
+       long sum = 0;
+       for_each_possible_cpu(i)
+               sum += per_cpu(mg_ctime_swaps, i);
+       return sum < 0 ? 0 : sum;
+}
+
 long get_nr_dirty_inodes(void)
 {
        /* not actually dirty inodes, but a wild approximation */
@@ -2655,6 +2697,7 @@ struct timespec64 inode_set_ctime_current(struct inode 
*inode)
 
                        /* Get a fine-grained time */
                        fine = ktime_get();
+                       this_cpu_inc(mg_fine_stamps);
 
                        /*
                         * If the cmpxchg works, we take the new floor value. If
@@ -2663,11 +2706,14 @@ 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))
+                               this_cpu_inc(mg_floor_swaps);
+                       else
                                fine = old;
                        now = ktime_mono_to_real(fine);
                }
        }
+       this_cpu_inc(mg_ctime_updates);
        now_ts = timestamp_truncate(ktime_to_timespec64(now), inode);
        cur = cns;
 
@@ -2682,6 +2728,7 @@ 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);
+               this_cpu_inc(mg_ctime_swaps);
        } else {
                /*
                 * Was the change due to someone marking the old ctime QUERIED?
@@ -2751,3 +2798,24 @@ 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)
+{
+       long ctime_updates = get_mg_ctime_updates();
+       long ctime_swaps = get_mg_ctime_swaps();
+       long fine_stamps = get_mg_fine_stamps();
+       long floor_swaps = 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);

-- 
2.45.2