lockdep: Reintroduce generation count to make BFS faster
We still can apply DaveM's generation count optimization to
BFS, based on the following idea:
- before doing each BFS, increase the global generation id
by 1
- if one node in the graph has been visited, mark it as
visited by storing the current global generation id into
the node's dep_gen_id field
- so we can decide if one node has been visited already, by
comparing the node's dep_gen_id with the global generation id.
By applying DaveM's generation count optimization to current
implementation of BFS, we gain the following advantages:
- we save MAX_LOCKDEP_ENTRIES/8 bytes memory;
- we remove the bitmap_zero(bfs_accessed, MAX_LOCKDEP_ENTRIES);
in each BFS, which is very time-consuming since
MAX_LOCKDEP_ENTRIES may be very large.(16384UL)
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "David S. Miller" <davem@davemloft.net>
LKML-Reference: <1248274089-6358-1-git-send-email-tom.leiming@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 0bb246e..2b443b5 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -861,14 +861,15 @@
};
static struct circular_queue lock_cq;
-static unsigned long bfs_accessed[BITS_TO_LONGS(MAX_LOCKDEP_ENTRIES)];
unsigned int max_bfs_queue_depth;
+static unsigned int lockdep_dependency_gen_id;
+
static inline void __cq_init(struct circular_queue *cq)
{
cq->front = cq->rear = 0;
- bitmap_zero(bfs_accessed, MAX_LOCKDEP_ENTRIES);
+ lockdep_dependency_gen_id++;
}
static inline int __cq_empty(struct circular_queue *cq)
@@ -914,7 +915,7 @@
nr = lock - list_entries;
WARN_ON(nr >= nr_list_entries);
lock->parent = parent;
- set_bit(nr, bfs_accessed);
+ lock->class->dep_gen_id = lockdep_dependency_gen_id;
}
static inline unsigned long lock_accessed(struct lock_list *lock)
@@ -923,7 +924,7 @@
nr = lock - list_entries;
WARN_ON(nr >= nr_list_entries);
- return test_bit(nr, bfs_accessed);
+ return lock->class->dep_gen_id == lockdep_dependency_gen_id;
}
static inline struct lock_list *get_lock_parent(struct lock_list *child)
@@ -3604,7 +3605,7 @@
sizeof(struct lock_chain) * MAX_LOCKDEP_CHAINS +
sizeof(struct list_head) * CHAINHASH_SIZE) / 1024
#ifdef CONFIG_PROVE_LOCKING
- + sizeof(struct circular_queue) + sizeof(bfs_accessed)
+ + sizeof(struct circular_queue)
#endif
);