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Subject[tip:core/locking] lockdep: Improve implementation of BFS
Commit-ID:  d588e46155e9c51217b9840db1e94a0f594c1af2
Gitweb: http://git.kernel.org/tip/d588e46155e9c51217b9840db1e94a0f594c1af2
Author: Ming Lei <tom.leiming@gmail.com>
AuthorDate: Thu, 16 Jul 2009 15:44:29 +0200
Committer: Peter Zijlstra <a.p.zijlstra@chello.nl>
CommitDate: Fri, 24 Jul 2009 10:49:46 +0200

lockdep: Improve implementation of BFS

1,replace %MAX_CIRCULAR_QUE_SIZE with &(MAX_CIRCULAR_QUE_SIZE-1)
since we define MAX_CIRCULAR_QUE_SIZE as power of 2;

2,use bitmap to mark if a lock is accessed in BFS in order to
clear it quickly, because we may search a graph many times.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1246201486-7308-3-git-send-email-tom.leiming@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
kernel/lockdep.c | 23 ++++++++++++++++-------
kernel/lockdep_internals.h | 35 +++++++++++++++++++++++------------
2 files changed, 39 insertions(+), 19 deletions(-)
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 93dc70d..5dcca26 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -42,7 +42,7 @@
#include <linux/hash.h>
#include <linux/ftrace.h>
#include <linux/stringify.h>
-
+#include <linux/bitops.h>
#include <asm/sections.h>

#include "lockdep_internals.h"
@@ -118,7 +118,7 @@ static inline int debug_locks_off_graph_unlock(void)
static int lockdep_initialized;

unsigned long nr_list_entries;
-static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES];
+struct lock_list list_entries[MAX_LOCKDEP_ENTRIES];

/*
* All data structures here are protected by the global debug_lock.
@@ -897,30 +897,38 @@ static int add_lock_to_list(struct lock_class *class, struct lock_class *this,
return 1;
}

+unsigned long bfs_accessed[BITS_TO_LONGS(MAX_LOCKDEP_ENTRIES)];
static struct circular_queue lock_cq;
+
static int __search_shortest_path(struct lock_list *source_entry,
struct lock_class *target,
struct lock_list **target_entry,
int forward)
{
struct lock_list *entry;
+ struct list_head *head;
struct circular_queue *cq = &lock_cq;
int ret = 1;

- __cq_init(cq);
-
- mark_lock_accessed(source_entry, NULL);
if (source_entry->class == target) {
*target_entry = source_entry;
ret = 0;
goto exit;
}

+ if (forward)
+ head = &source_entry->class->locks_after;
+ else
+ head = &source_entry->class->locks_before;
+
+ if (list_empty(head))
+ goto exit;
+
+ __cq_init(cq);
__cq_enqueue(cq, (unsigned long)source_entry);

while (!__cq_empty(cq)) {
struct lock_list *lock;
- struct list_head *head;

__cq_dequeue(cq, (unsigned long *)&lock);

@@ -1040,6 +1048,7 @@ static noinline int print_circular_bug(void)
return 0;

this.class = hlock_class(check_source);
+ this.parent = NULL;
if (!save_trace(&this.trace))
return 0;

@@ -1580,10 +1589,10 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
*/
check_source = next;
check_target = prev;
+
if (check_noncircular(hlock_class(next), 0) == 2)
return print_circular_bug();

-
if (!check_prev_add_irq(curr, prev, next))
return 0;

diff --git a/kernel/lockdep_internals.h b/kernel/lockdep_internals.h
index 6f48d37..c2f6594 100644
--- a/kernel/lockdep_internals.h
+++ b/kernel/lockdep_internals.h
@@ -137,23 +137,28 @@ extern atomic_t nr_find_usage_backwards_recursions;
# define debug_atomic_read(ptr) 0
#endif

+
+extern unsigned long nr_list_entries;
+extern struct lock_list list_entries[MAX_LOCKDEP_ENTRIES];
+extern unsigned long bfs_accessed[];
+
+/*For good efficiency of modular, we use power of 2*/
+#define MAX_CIRCULAR_QUE_SIZE 4096UL
+
/* The circular_queue and helpers is used to implement the
* breadth-first search(BFS)algorithem, by which we can build
* the shortest path from the next lock to be acquired to the
* previous held lock if there is a circular between them.
* */
-#define MAX_CIRCULAR_QUE_SIZE 4096UL
struct circular_queue{
unsigned long element[MAX_CIRCULAR_QUE_SIZE];
unsigned int front, rear;
};

-#define LOCK_ACCESSED 1UL
-#define LOCK_ACCESSED_MASK (~LOCK_ACCESSED)
-
static inline void __cq_init(struct circular_queue *cq)
{
cq->front = cq->rear = 0;
+ bitmap_zero(bfs_accessed, MAX_LOCKDEP_ENTRIES);
}

static inline int __cq_empty(struct circular_queue *cq)
@@ -163,7 +168,7 @@ static inline int __cq_empty(struct circular_queue *cq)

static inline int __cq_full(struct circular_queue *cq)
{
- return ((cq->rear + 1)%MAX_CIRCULAR_QUE_SIZE) == cq->front;
+ return ((cq->rear + 1)&(MAX_CIRCULAR_QUE_SIZE-1)) == cq->front;
}

static inline int __cq_enqueue(struct circular_queue *cq, unsigned long elem)
@@ -172,7 +177,7 @@ static inline int __cq_enqueue(struct circular_queue *cq, unsigned long elem)
return -1;

cq->element[cq->rear] = elem;
- cq->rear = (cq->rear + 1)%MAX_CIRCULAR_QUE_SIZE;
+ cq->rear = (cq->rear + 1)&(MAX_CIRCULAR_QUE_SIZE-1);
return 0;
}

@@ -182,30 +187,36 @@ static inline int __cq_dequeue(struct circular_queue *cq, unsigned long *elem)
return -1;

*elem = cq->element[cq->front];
- cq->front = (cq->front + 1)%MAX_CIRCULAR_QUE_SIZE;
+ cq->front = (cq->front + 1)&(MAX_CIRCULAR_QUE_SIZE-1);
return 0;
}

static inline int __cq_get_elem_count(struct circular_queue *cq)
{
- return (cq->rear - cq->front)%MAX_CIRCULAR_QUE_SIZE;
+ return (cq->rear - cq->front)&(MAX_CIRCULAR_QUE_SIZE-1);
}

static inline void mark_lock_accessed(struct lock_list *lock,
struct lock_list *parent)
{
- lock->parent = (void *) parent + LOCK_ACCESSED;
+ unsigned long nr;
+ nr = lock - list_entries;
+ WARN_ON(nr >= nr_list_entries);
+ lock->parent = parent;
+ set_bit(nr, bfs_accessed);
}

static inline unsigned long lock_accessed(struct lock_list *lock)
{
- return (unsigned long)lock->parent & LOCK_ACCESSED;
+ unsigned long nr;
+ nr = lock - list_entries;
+ WARN_ON(nr >= nr_list_entries);
+ return test_bit(nr, bfs_accessed);
}

static inline struct lock_list *get_lock_parent(struct lock_list *child)
{
- return (struct lock_list *)
- ((unsigned long)child->parent & LOCK_ACCESSED_MASK);
+ return child->parent;
}

static inline unsigned long get_lock_depth(struct lock_list *child)

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