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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2009-01-12 08:01:47 -0500
committerIngo Molnar <mingo@elte.hu>2009-01-14 12:09:02 -0500
commit0d66bf6d3514b35eb6897629059443132992dbd7 (patch)
treea47ee0fc3299361cf3b222c8242741adfedaab74 /kernel/mutex.h
parent41719b03091911028116155deddc5eedf8c45e37 (diff)
mutex: implement adaptive spinning
Change mutex contention behaviour such that it will sometimes busy wait on acquisition - moving its behaviour closer to that of spinlocks. This concept got ported to mainline from the -rt tree, where it was originally implemented for rtmutexes by Steven Rostedt, based on work by Gregory Haskins. Testing with Ingo's test-mutex application (http://lkml.org/lkml/2006/1/8/50) gave a 345% boost for VFS scalability on my testbox: # ./test-mutex-shm V 16 10 | grep "^avg ops" avg ops/sec: 296604 # ./test-mutex-shm V 16 10 | grep "^avg ops" avg ops/sec: 85870 The key criteria for the busy wait is that the lock owner has to be running on a (different) cpu. The idea is that as long as the owner is running, there is a fair chance it'll release the lock soon, and thus we'll be better off spinning instead of blocking/scheduling. Since regular mutexes (as opposed to rtmutexes) do not atomically track the owner, we add the owner in a non-atomic fashion and deal with the races in the slowpath. Furthermore, to ease the testing of the performance impact of this new code, there is means to disable this behaviour runtime (without having to reboot the system), when scheduler debugging is enabled (CONFIG_SCHED_DEBUG=y), by issuing the following command: # echo NO_OWNER_SPIN > /debug/sched_features This command re-enables spinning again (this is also the default): # echo OWNER_SPIN > /debug/sched_features Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/mutex.h')
-rw-r--r--kernel/mutex.h22
1 files changed, 20 insertions, 2 deletions
diff --git a/kernel/mutex.h b/kernel/mutex.h
index a075dafbb290..67578ca48f94 100644
--- a/kernel/mutex.h
+++ b/kernel/mutex.h
@@ -16,8 +16,26 @@
16#define mutex_remove_waiter(lock, waiter, ti) \ 16#define mutex_remove_waiter(lock, waiter, ti) \
17 __list_del((waiter)->list.prev, (waiter)->list.next) 17 __list_del((waiter)->list.prev, (waiter)->list.next)
18 18
19#define debug_mutex_set_owner(lock, new_owner) do { } while (0) 19#ifdef CONFIG_SMP
20#define debug_mutex_clear_owner(lock) do { } while (0) 20static inline void mutex_set_owner(struct mutex *lock)
21{
22 lock->owner = current_thread_info();
23}
24
25static inline void mutex_clear_owner(struct mutex *lock)
26{
27 lock->owner = NULL;
28}
29#else
30static inline void mutex_set_owner(struct mutex *lock)
31{
32}
33
34static inline void mutex_clear_owner(struct mutex *lock)
35{
36}
37#endif
38
21#define debug_mutex_wake_waiter(lock, waiter) do { } while (0) 39#define debug_mutex_wake_waiter(lock, waiter) do { } while (0)
22#define debug_mutex_free_waiter(waiter) do { } while (0) 40#define debug_mutex_free_waiter(waiter) do { } while (0)
23#define debug_mutex_add_waiter(lock, waiter, ti) do { } while (0) 41#define debug_mutex_add_waiter(lock, waiter, ti) do { } while (0)