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lockdep: Reintroduce generation count to make BFS faster

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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
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1
include/linux/lockdep.h
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@@ -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: