0d66bf6d35
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>
49 lines
1.3 KiB
C
49 lines
1.3 KiB
C
/*
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* Mutexes: blocking mutual exclusion locks
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*
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* started by Ingo Molnar:
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*
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* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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*
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* This file contains mutex debugging related internal prototypes, for the
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* !CONFIG_DEBUG_MUTEXES case. Most of them are NOPs:
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*/
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#define spin_lock_mutex(lock, flags) \
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do { spin_lock(lock); (void)(flags); } while (0)
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#define spin_unlock_mutex(lock, flags) \
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do { spin_unlock(lock); (void)(flags); } while (0)
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#define mutex_remove_waiter(lock, waiter, ti) \
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__list_del((waiter)->list.prev, (waiter)->list.next)
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#ifdef CONFIG_SMP
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static inline void mutex_set_owner(struct mutex *lock)
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{
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lock->owner = current_thread_info();
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}
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static inline void mutex_clear_owner(struct mutex *lock)
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{
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lock->owner = NULL;
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}
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#else
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static inline void mutex_set_owner(struct mutex *lock)
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{
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}
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static inline void mutex_clear_owner(struct mutex *lock)
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{
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}
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#endif
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#define debug_mutex_wake_waiter(lock, waiter) do { } while (0)
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#define debug_mutex_free_waiter(waiter) do { } while (0)
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#define debug_mutex_add_waiter(lock, waiter, ti) do { } while (0)
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#define debug_mutex_unlock(lock) do { } while (0)
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#define debug_mutex_init(lock, name, key) do { } while (0)
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static inline void
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debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
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{
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}
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