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Commit e351b660 authored by Ming Lei's avatar Ming Lei Committed by Ingo Molnar
Browse files

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: default avatarMing Lei <tom.leiming@gmail.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@elte.hu>
parent bb97a91e

include/linux/lockdep.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -58,6 +58,7 @@ struct lock_class { 




	struct lockdep_subclass_key	*key;

	struct lockdep_subclass_key	*key;

	unsigned int			subclass;

	unsigned int			subclass;

	unsigned int			dep_gen_id;





	/*

	/*

	 * IRQ/softirq usage tracking bits:

	 * IRQ/softirq usage tracking bits:

kernel/lockdep.c

+6 −5
Original line number Original line Diff line number Diff line
@@ -861,14 +861,15 @@ struct circular_queue { 
};

};





static struct circular_queue lock_cq;

static struct circular_queue lock_cq;

static unsigned long bfs_accessed[BITS_TO_LONGS(MAX_LOCKDEP_ENTRIES)];





unsigned int max_bfs_queue_depth;

unsigned int max_bfs_queue_depth;





static unsigned int lockdep_dependency_gen_id;



static inline void __cq_init(struct circular_queue *cq)

static inline void __cq_init(struct circular_queue *cq)

{

{

	cq->front = cq->rear = 0;

	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)

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;

	nr = lock - list_entries;

	WARN_ON(nr >= nr_list_entries);

	WARN_ON(nr >= nr_list_entries);

	lock->parent = parent;

	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)

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;

	nr = lock - list_entries;

	WARN_ON(nr >= nr_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)

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 lock_chain) * MAX_LOCKDEP_CHAINS +

		sizeof(struct list_head) * CHAINHASH_SIZE) / 1024

		sizeof(struct list_head) * CHAINHASH_SIZE) / 1024

#ifdef CONFIG_PROVE_LOCKING

#ifdef CONFIG_PROVE_LOCKING

		+ sizeof(struct circular_queue) + sizeof(bfs_accessed)

		+ sizeof(struct circular_queue)

#endif

#endif

		);

		);