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mutex类似于互斥信号量。oqs 可以对mutex 性能有所优化，具体分析如下：首先mutex锁在kernel中有两种初始化方式，分别为：静态方式：#define DEFINE_MUTEX(mutexname) \	struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)其中动态方式：#define mutex_init(mutex)						\do {									\	static struct lock_class_key __key;				\									\	__mutex_init((mutex), #mutex, &__key);				\} while (0)我们这里以动态方式为例void__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key){	atomic_long_set(&lock->owner, 0);	spin_lock_init(&lock->wait_lock);	INIT_LIST_HEAD(&lock->wait_list);#ifdef CONFIG_MUTEX_SPIN_ON_OWNER	osq_lock_init(&lock->osq);#endif	debug_mutex_init(lock, name, key);}可以看到在__mutex_init 中有定义一个原子变量lock->owner，一个spinlock 锁lock->wait_lock，一个list lock->wait_list。其中debug_mutex_init 用于debug，默认情况下为空函数.如使能CONFIG_MUTEX_SPIN_ON_OWNER的话，还定义了一个osq锁.下来我们看看mutex如何获得锁void __sched mutex_lock(struct mutex *lock){	#获得mutex锁的过程可能会sleep	might_sleep();	#从这里知道mutex 锁 可以分为fast或者slow方式获得锁，如果之前没有人占用锁，就走的是fast方式	if (!__mutex_trylock_fast(lock))		__mutex_lock_slowpath(lock);}我们看看mutex 如何快速获得mutex锁static __always_inline bool __mutex_trylock_fast(struct mutex *lock){	unsigned long curr = (unsigned long)current;	#这里会比较lock->owner的值是否等于0，如果等于零的话，则将curr赋值给lock->owner，并返回lock->owner 原来的值零，	#所以这里if 条件成立，返回true	if (!atomic_long_cmpxchg_acquire(&lock->owner, 0UL, curr))		return true;	return false;}原来fast方式获得mutex锁就是判断lock->owner 是否为零下来我们再看看slow方式获得mutex锁的过程static noinline void __sched__mutex_lock_slowpath(struct mutex *lock){	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);}static int __sched__mutex_lock(struct mutex *lock, long state, unsigned int subclass,	     struct lockdep_map *nest_lock, unsigned long ip){	return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);}__mutex_lock_common 这个函数很长很长，我们只看osq 部分static __always_inline int __sched__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,		    struct lockdep_map *nest_lock, unsigned long ip,		    struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx){	#再次检查是否可以快速获得锁，如果不能的话，则通过osp开得到锁	if (__mutex_trylock(lock) ||	    mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {		/* got the lock, yay! */		lock_acquired(&lock->dep_map, ip);		if (use_ww_ctx && ww_ctx)			ww_mutex_set_context_fastpath(ww, ww_ctx);		preempt_enable();		return 0;	}	}osq获得锁的函数如下：		static __always_inline boolmutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,		      const bool use_ww_ctx, struct mutex_waiter *waiter){	if (!waiter) {		/*		 * The purpose of the mutex_can_spin_on_owner() function is		 * to eliminate the overhead of osq_lock() and osq_unlock()		 * in case spinning isn't possible. As a waiter-spinner		 * is not going to take OSQ lock anyway, there is no need		 * to call mutex_can_spin_on_owner().		 */		 #检查当前持有锁的ower并没有运行，而是在临界区执行		if (!mutex_can_spin_on_owner(lock))			goto fail;		/*		 * In order to avoid a stampede of mutex spinners trying to		 * acquire the mutex all at once, the spinners need to take a		 * MCS (queued) lock first before spinning on the owner field.		 */		 #获得osq锁		if (!osq_lock(&lock->osq))			goto fail;	}	for (;;) {		struct task_struct *owner;		/* Try to acquire the mutex... */		#尝试获得mutex，当ower为null是获得锁		owner = __mutex_trylock_or_owner(lock);		if (!owner)			break;		/*		 * There's an owner, wait for it to either		 * release the lock or go to sleep.		 */		 #等待前面获得ower来释放锁或者sleep		if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))			goto fail_unlock;		/*		 * The cpu_relax() call is a compiler barrier which forces		 * everything in this loop to be re-loaded. We don't need		 * memory barriers as we'll eventually observe the right		 * values at the cost of a few extra spins.		 */		cpu_relax();	}#正常情况解锁osq并返回	if (!waiter)		osq_unlock(&lock->osq);	return true;fail_unlock:	if (!waiter)		osq_unlock(&lock->osq);fail:	/*	 * If we fell out of the spin path because of need_resched(),	 * reschedule now, before we try-lock the mutex. This avoids getting	 * scheduled out right after we obtained the mutex.	 */	 #当获得osq锁失败的时候，如果需要调度，则sleep一段时间并让出cpu，并返回failed。	if (need_resched()) {		/*		 * We _should_ have TASK_RUNNING here, but just in case		 * we do not, make it so, otherwise we might get stuck.		 */		__set_current_state(TASK_RUNNING);		schedule_preempt_disabled();	}	return false;}从这里看在mutex slow path中如果使能osq的话，可以使用osq来优化mutex的性能

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