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authorHitoshi Mitake <mitake@dcl.info.waseda.ac.jp>2010-10-05 18:01:51 +0900
committerIngo Molnar <mingo@elte.hu>2010-10-18 18:44:25 +0200
commit620162505e5d46bc4494b1761743e4b0b3bf8e16 (patch)
tree462e6d2ecdcfdaa117c5b926325a0ce1d565571e /kernel/lockdep.c
parentf2f108eb4511f22a6f7568090cfcf4e7b2dc0f62 (diff)
lockdep: Add improved subclass caching
Current lockdep_map only caches one class with subclass == 0, and looks up hash table of classes when subclass != 0. It seems that this has no problem because the case of subclass != 0 is rare. But locks of struct rq are acquired with subclass == 1 when task migration is executed. Task migration is high frequent event, so I modified lockdep to cache subclasses. I measured the score of perf bench sched messaging. This patch has slightly but certain (order of milli seconds or 10 milli seconds) effect when lots of tasks are running. I'll show the result in the tail of this description. NR_LOCKDEP_CACHING_CLASSES specifies how many classes can be cached in the instances of lockdep_map. I discussed with Peter Zijlstra in LinuxCon Japan about this approach and he taught me that caching every subclasses(8) is cleary waste of memory. So number of cached classes should be configurable. === Score comparison of benchmarks === # "min" means best score, and "max" means worst score for i in `seq 1 10`; do ./perf bench -f simple sched messaging; done before: min: 0.565000, max: 0.583000, avg: 0.572500 after: min: 0.559000, max: 0.568000, avg: 0.563300 # with more processes for i in `seq 1 10`; do ./perf bench -f simple sched messaging -g 40; done before: min: 2.274000, max: 2.298000, avg: 2.286300 after: min: 2.242000, max: 2.270000, avg: 2.259700 Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <1286269311-28336-2-git-send-email-mitake@dcl.info.waseda.ac.jp> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/lockdep.c')
-rw-r--r--kernel/lockdep.c25
1 files changed, 18 insertions, 7 deletions
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 84baa71cfda..bc4d32871f9 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -774,7 +774,9 @@ out_unlock_set:
raw_local_irq_restore(flags);
if (!subclass || force)
- lock->class_cache = class;
+ lock->class_cache[0] = class;
+ else if (subclass < NR_LOCKDEP_CACHING_CLASSES)
+ lock->class_cache[subclass] = class;
if (DEBUG_LOCKS_WARN_ON(class->subclass != subclass))
return NULL;
@@ -2679,7 +2681,11 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
void lockdep_init_map(struct lockdep_map *lock, const char *name,
struct lock_class_key *key, int subclass)
{
- lock->class_cache = NULL;
+ int i;
+
+ for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++)
+ lock->class_cache[i] = NULL;
+
#ifdef CONFIG_LOCK_STAT
lock->cpu = raw_smp_processor_id();
#endif
@@ -2750,10 +2756,10 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
if (lock->key == &__lockdep_no_validate__)
check = 1;
- if (!subclass)
- class = lock->class_cache;
+ if (subclass < NR_LOCKDEP_CACHING_CLASSES)
+ class = lock->class_cache[subclass];
/*
- * Not cached yet or subclass?
+ * Not cached?
*/
if (unlikely(!class)) {
class = register_lock_class(lock, subclass, 0);
@@ -2918,7 +2924,7 @@ static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
return 1;
if (hlock->references) {
- struct lock_class *class = lock->class_cache;
+ struct lock_class *class = lock->class_cache[0];
if (!class)
class = look_up_lock_class(lock, 0);
@@ -3559,7 +3565,12 @@ void lockdep_reset_lock(struct lockdep_map *lock)
if (list_empty(head))
continue;
list_for_each_entry_safe(class, next, head, hash_entry) {
- if (unlikely(class == lock->class_cache)) {
+ int match = 0;
+
+ for (j = 0; j < NR_LOCKDEP_CACHING_CLASSES; j++)
+ match |= class == lock->class_cache[j];
+
+ if (unlikely(match)) {
if (debug_locks_off_graph_unlock())
WARN_ON(1);
goto out_restore;