linux-kernel - [PATCH] lockdep: do not count lock class operations without CONFIG_DEBUG

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Date:   Fri, 19 May 2017 10:06:01 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: [PATCH] lockdep: do not count lock class operations without
 CONFIG_DEBUG_LOCKDEP

Currently this counter shown in /proc/lockdep if CONFIG_DEBUG_LOCKDEP=y
This patch disables it completely if this option is disabled.

This counter might be useful for debugging lockdep itself, but for normal
debugging it seems useless. Lockstat provides more detailed statistics.

This atomic_inc is a hot spot inside __lock_acquire() for debug kernel.

With patch "netperf -H localhost" shows some boost: 2500 -> 2600

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
---
 kernel/locking/lockdep.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c0e31bfee25c..60bd16984546 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1375,7 +1375,9 @@ static void print_lock_class_header(struct lock_class *class, int depth)
 
 	printk("%*s->", depth, "");
 	print_lock_name(class);
+#ifdef CONFIG_DEBUG_LOCKDEP
 	printk(KERN_CONT " ops: %lu", class->ops);
+#endif
 	printk(KERN_CONT " {\n");
 
 	for (bit = 0; bit < LOCK_USAGE_STATES; bit++) {
@@ -3256,7 +3258,9 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 		if (!class)
 			return 0;
 	}
+#ifdef CONFIG_DEBUG_LOCKDEP
 	atomic_inc((atomic_t *)&class->ops);
+#endif
 	if (very_verbose(class)) {
 		printk("\nacquire class [%p] %s", class->key, class->name);
 		if (class->name_version > 1)