lockstat: human readability tweaks

Present all this fancy new lock statistics information:

*warning, _wide_ output ahead*

(output edited for purpose of brevity)

 # cat /proc/lock_stat
lock_stat version 0.1
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
                              class name    contentions   waittime-min   waittime-max waittime-total   acquisitions   holdtime-min   holdtime-max holdtime-total
-----------------------------------------------------------------------------------------------------------------------------------------------------------------

                         &inode->i_mutex:         14458           6.57      398832.75     2469412.23        6768876           0.34    11398383.65   339410830.89
                         ---------------
                         &inode->i_mutex           4486          [<ffffffff802a08f9>] pipe_wait+0x86/0x8d
                         &inode->i_mutex              0          [<ffffffff802a01e8>] pipe_write_fasync+0x29/0x5d
                         &inode->i_mutex              0          [<ffffffff802a0e18>] pipe_read+0x74/0x3a5
                         &inode->i_mutex              0          [<ffffffff802a1a6a>] do_lookup+0x81/0x1ae

.................................................................................................................................................................

              &inode->i_data.tree_lock-W:           491           0.27          62.47         493.89        2477833           0.39         468.89     1146584.25
              &inode->i_data.tree_lock-R:            65           0.44           4.27          48.78       26288792           0.36         184.62    10197458.24
              --------------------------
                &inode->i_data.tree_lock             46          [<ffffffff80277095>] __do_page_cache_readahead+0x69/0x24f
                &inode->i_data.tree_lock             31          [<ffffffff8026f9fb>] add_to_page_cache+0x31/0xba
                &inode->i_data.tree_lock              0          [<ffffffff802770ee>] __do_page_cache_readahead+0xc2/0x24f
                &inode->i_data.tree_lock              0          [<ffffffff8026f6e4>] find_get_page+0x1a/0x58

.................................................................................................................................................................

                      proc_inum_idr.lock:             0           0.00           0.00           0.00             36           0.00          65.60         148.26
                        proc_subdir_lock:             0           0.00           0.00           0.00        3049859           0.00         106.81     1563212.42
                        shrinker_rwsem-W:             0           0.00           0.00           0.00              5           0.00           1.73           3.68
                        shrinker_rwsem-R:             0           0.00           0.00           0.00            633           2.57         246.57       10909.76

'contentions' and 'acquisitions' are the number of such events measured (since
the last reset). The waittime- and holdtime- (min, max, total) numbers are
presented in microseconds.

If there are any contention points, the lock class is presented in the block
format (as i_mutex and tree_lock above), otherwise a single line of output is
presented.

The output is sorted on absolute number of contentions (read + write), this
should get the worst offenders presented first, so that:

 # grep : /proc/lock_stat | head

will quickly show who's bad.

The stats can be reset using:

 # echo 0 > /proc/lock_stat

[bunk@stusta.de: make 2 functions static]
[akpm@linux-foundation.org: fix printk warning]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 44 insertions, 0 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 70ca4db28af..a8dc99d9fef 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -149,6 +149,50 @@ static void lock_time_inc(struct lock_time *lt, s64 time)
 	lt->nr++;
 }
 
+static inline void lock_time_add(struct lock_time *src, struct lock_time *dst)
+{
+	dst->min += src->min;
+	dst->max += src->max;
+	dst->total += src->total;
+	dst->nr += src->nr;
+}
+
+struct lock_class_stats lock_stats(struct lock_class *class)
+{
+	struct lock_class_stats stats;
+	int cpu, i;
+
+	memset(&stats, 0, sizeof(struct lock_class_stats));
+	for_each_possible_cpu(cpu) {
+		struct lock_class_stats *pcs =
+			&per_cpu(lock_stats, cpu)[class - lock_classes];
+
+		for (i = 0; i < ARRAY_SIZE(stats.contention_point); i++)
+			stats.contention_point[i] += pcs->contention_point[i];
+
+		lock_time_add(&pcs->read_waittime, &stats.read_waittime);
+		lock_time_add(&pcs->write_waittime, &stats.write_waittime);
+
+		lock_time_add(&pcs->read_holdtime, &stats.read_holdtime);
+		lock_time_add(&pcs->write_holdtime, &stats.write_holdtime);
+	}
+
+	return stats;
+}
+
+void clear_lock_stats(struct lock_class *class)
+{
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		struct lock_class_stats *cpu_stats =
+			&per_cpu(lock_stats, cpu)[class - lock_classes];
+
+		memset(cpu_stats, 0, sizeof(struct lock_class_stats));
+	}
+	memset(class->contention_point, 0, sizeof(class->contention_point));
+}
+
 static struct lock_class_stats *get_lock_stats(struct lock_class *class)
 {
 	return &get_cpu_var(lock_stats)[class - lock_classes];