>From e615f62dfa155cbf9c04318f146570047f2c0c0c Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Wed, 3 Oct 2018 11:36:24 -0400 Subject: [PATCH v3 4/5] locking/lockdep: Make class->ops a percpu counter A sizable portion of the CPU cycles spent on the __lock_acquire() is used up by the atomic increment of class->ops stat counter. By taking it out from the lock_class structure and changing it to a per-cpu per-lock-class counter, we can reduce the amount of cacheline contention on the class structure when multiple CPUs are trying to acquire locks of the same class simultaneously. To limit the increase in memory consumption because of the percpu nature of that counter, it is now put back under the CONFIG_DEBUG_LOCKDEP config option. So the memory consumption increase will only occur if CONFIG_DEBUG_LOCKDEP is defined. The lock_class structure, however, is reduced in size by 16 bytes on 64-bit archs after ops removal and a minor restructuring of the fields. This patch also fixes a bug in the increment code as the counter is of the unsigned long type, but atomic_inc() was used to increment it. v3: Move lock_class_ops[] into lockdep_stats structure. Signed-off-by: Waiman Long --- include/linux/lockdep.h | 7 +------ kernel/locking/lockdep.c | 11 ++++++++--- kernel/locking/lockdep_internals.h | 27 +++++++++++++++++++++++++++ kernel/locking/lockdep_proc.c | 2 +- 4 files changed, 37 insertions(+), 10 deletions(-) diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index b0d0b51c4d85..1fd82ff99c65 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -99,13 +99,8 @@ struct lock_class { */ unsigned int version; - /* - * Statistics counter: - */ - unsigned long ops; - - const char *name; int name_version; + const char *name; #ifdef CONFIG_LOCK_STAT unsigned long contention_point[LOCKSTAT_POINTS]; diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index b7774ff2516f..57e3f153474f 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -138,7 +138,7 @@ static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES]; * get freed - this significantly simplifies the debugging code. */ unsigned long nr_lock_classes; -static struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; +struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; static inline struct lock_class *hlock_class(struct held_lock *hlock) { @@ -435,6 +435,7 @@ unsigned int max_lockdep_depth; * Various lockdep statistics: */ DEFINE_PER_CPU(struct lockdep_stats, lockdep_stats); +DEFINE_PER_CPU(unsigned long [MAX_LOCKDEP_KEYS], lock_class_ops); #endif /* @@ -1391,7 +1392,9 @@ static void print_lock_class_header(struct lock_class *class, int depth) printk("%*s->", depth, ""); print_lock_name(class); - printk(KERN_CONT " ops: %lu", class->ops); +#ifdef CONFIG_DEBUG_LOCKDEP + printk(KERN_CONT " ops: %lu", debug_class_ops_read(class)); +#endif printk(KERN_CONT " {\n"); for (bit = 0; bit < LOCK_USAGE_STATES; bit++) { @@ -3226,7 +3229,9 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, if (!class) return 0; } - atomic_inc((atomic_t *)&class->ops); + + debug_class_ops_inc(class); + if (very_verbose(class)) { printk("\nacquire class [%px] %s", class->key, class->name); if (class->name_version > 1) diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h index d459d624ba2a..88c847a41c8a 100644 --- a/kernel/locking/lockdep_internals.h +++ b/kernel/locking/lockdep_internals.h @@ -152,9 +152,15 @@ struct lockdep_stats { int nr_find_usage_forwards_recursions; int nr_find_usage_backwards_checks; int nr_find_usage_backwards_recursions; + + /* + * Per lock class locking operation stat counts + */ + unsigned long lock_class_ops[MAX_LOCKDEP_KEYS]; }; DECLARE_PER_CPU(struct lockdep_stats, lockdep_stats); +extern struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; #define __debug_atomic_inc(ptr) \ this_cpu_inc(lockdep_stats.ptr); @@ -179,9 +185,30 @@ DECLARE_PER_CPU(struct lockdep_stats, lockdep_stats); } \ __total; \ }) + +static inline void debug_class_ops_inc(struct lock_class *class) +{ + int idx; + + idx = class - lock_classes; + __debug_atomic_inc(lock_class_ops[idx]); +} + +static inline unsigned long debug_class_ops_read(struct lock_class *class) +{ + int idx, cpu; + unsigned long ops = 0; + + idx = class - lock_classes; + for_each_possible_cpu(cpu) + ops += per_cpu(lockdep_stats.lock_class_ops[idx], cpu); + return ops; +} + #else # define __debug_atomic_inc(ptr) do { } while (0) # define debug_atomic_inc(ptr) do { } while (0) # define debug_atomic_dec(ptr) do { } while (0) # define debug_atomic_read(ptr) 0 +# define debug_class_ops_inc(ptr) do { } while (0) #endif diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c index 3dd980dfba2d..3d31f9b0059e 100644 --- a/kernel/locking/lockdep_proc.c +++ b/kernel/locking/lockdep_proc.c @@ -68,7 +68,7 @@ static int l_show(struct seq_file *m, void *v) seq_printf(m, "%p", class->key); #ifdef CONFIG_DEBUG_LOCKDEP - seq_printf(m, " OPS:%8ld", class->ops); + seq_printf(m, " OPS:%8ld", debug_class_ops_read(class)); #endif #ifdef CONFIG_PROVE_LOCKING seq_printf(m, " FD:%5ld", lockdep_count_forward_deps(class)); -- 2.18.0