From 0d66bf6d3514b35eb6897629059443132992dbd7 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 12 Jan 2009 14:01:47 +0100 Subject: 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 Signed-off-by: Ingo Molnar --- include/linux/mutex.h | 5 +++-- include/linux/sched.h | 1 + 2 files changed, 4 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/linux/mutex.h b/include/linux/mutex.h index 7a0e5c4..3069ec7 100644 --- a/include/linux/mutex.h +++ b/include/linux/mutex.h @@ -50,8 +50,10 @@ struct mutex { atomic_t count; spinlock_t wait_lock; struct list_head wait_list; -#ifdef CONFIG_DEBUG_MUTEXES +#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP) struct thread_info *owner; +#endif +#ifdef CONFIG_DEBUG_MUTEXES const char *name; void *magic; #endif @@ -68,7 +70,6 @@ struct mutex_waiter { struct list_head list; struct task_struct *task; #ifdef CONFIG_DEBUG_MUTEXES - struct mutex *lock; void *magic; #endif }; diff --git a/include/linux/sched.h b/include/linux/sched.h index 9f0b372..c34b137 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -330,6 +330,7 @@ extern signed long schedule_timeout_killable(signed long timeout); extern signed long schedule_timeout_uninterruptible(signed long timeout); asmlinkage void __schedule(void); asmlinkage void schedule(void); +extern int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner); struct nsproxy; struct user_namespace; -- cgit v1.1