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| author | David Miller <davem@davemloft.net> | 2008-07-29 21:45:03 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-07-31 18:38:28 +0200 |
| commit | 419ca3f13532793b81aff09f80c60af3eacbb43d (patch) | |
| tree | eb2d82e52917ebccff269a51e90868ce229336b2 /kernel/lockdep_internals.h | |
| parent | 6e86841d05f371b5b9b86ce76c02aaee83352298 (diff) | |
| download | lwn-419ca3f13532793b81aff09f80c60af3eacbb43d.tar.gz lwn-419ca3f13532793b81aff09f80c60af3eacbb43d.zip | |
lockdep: fix combinatorial explosion in lock subgraph traversal
When we traverse the graph, either forwards or backwards, we
are interested in whether a certain property exists somewhere
in a node reachable in the graph.
Therefore it is never necessary to traverse through a node more
than once to get a correct answer to the given query.
Take advantage of this property using a global ID counter so that we
need not clear all the markers in all the lock_class entries before
doing a traversal. A new ID is choosen when we start to traverse, and
we continue through a lock_class only if it's ID hasn't been marked
with the new value yet.
This short-circuiting is essential especially for high CPU count
systems. The scheduler has a runqueue per cpu, and needs to take
two runqueue locks at a time, which leads to long chains of
backwards and forwards subgraphs from these runqueue lock nodes.
Without the short-circuit implemented here, a graph traversal on
a runqueue lock can take up to (1 << (N - 1)) checks on a system
with N cpus.
For anything more than 16 cpus or so, lockdep will eventually bring
the machine to a complete standstill.
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/lockdep_internals.h')
| -rw-r--r-- | kernel/lockdep_internals.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/lockdep_internals.h b/kernel/lockdep_internals.h index c3600a091a28..68d44ec77ab5 100644 --- a/kernel/lockdep_internals.h +++ b/kernel/lockdep_internals.h @@ -53,6 +53,9 @@ extern unsigned int nr_process_chains; extern unsigned int max_lockdep_depth; extern unsigned int max_recursion_depth; +extern unsigned long lockdep_count_forward_deps(struct lock_class *); +extern unsigned long lockdep_count_backward_deps(struct lock_class *); + #ifdef CONFIG_DEBUG_LOCKDEP /* * Various lockdep statistics: |