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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>
This commit is contained in:
Ming Lei 2009-07-22 22:48:09 +08:00 committed by Ingo Molnar
parent bb97a91e25
commit e351b660fd
2 changed files with 7 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/lockdep.h
View File

@ -58,6 +58,7 @@ struct lock_class {
struct lockdep_subclass_key *key;
unsigned int subclass;
unsigned int dep_gen_id;
/*
* IRQ/softirq usage tracking bits:

11
kernel/lockdep.c
View File

@ -861,14 +861,15 @@ struct circular_queue {
};
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 @@ static inline void mark_lock_accessed(struct lock_list *lock,
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 @@ static inline unsigned long lock_accessed(struct lock_list *lock)
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 @@ void __init lockdep_info(void)
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
);