[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v9 09/19] qspinlock: Prepare for unfair lock support
If unfair lock is supported, the lock acquisition loop at the end of the queue_spin_lock_slowpath() function may need to detect the fact the lock can be stolen. Code are added for the stolen lock detection. Signed-off-by: Waiman Long <Waiman.Long@xxxxxx> --- kernel/locking/qspinlock.c | 26 +++++++++++++++++++------- 1 files changed, 19 insertions(+), 7 deletions(-) diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 994358c..eab005a 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -68,6 +68,7 @@ struct qnode { struct mcs_spinlock mcs; }; +#define qhead mcs.locked /* The queue head flag */ /* * Per-CPU queue node structures; we can never have more than 4 nested @@ -220,18 +221,20 @@ xchg_tail(struct qspinlock *lock, u32 tail, u32 *pval) /** * get_qlock - Set the lock bit and own the lock - * @lock: Pointer to queue spinlock structure + * @lock : Pointer to queue spinlock structure + * Return: 1 if lock acquired, 0 otherwise * * This routine should only be called when the caller is the only one * entitled to acquire the lock. */ -static __always_inline void get_qlock(struct qspinlock *lock) +static __always_inline int get_qlock(struct qspinlock *lock) { struct __qspinlock *l = (void *)lock; barrier(); ACCESS_ONCE(l->locked) = _Q_LOCKED_VAL; barrier(); + return 1; } /** @@ -366,7 +369,7 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) tail = encode_tail(smp_processor_id(), idx); node += idx; - node->mcs.locked = 0; + node->qhead = 0; node->mcs.next = NULL; /* @@ -392,7 +395,7 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) prev = decode_tail(old); ACCESS_ONCE(prev->mcs.next) = (struct mcs_spinlock *)node; - while (!smp_load_acquire(&node->mcs.locked)) + while (!smp_load_acquire(&node->qhead)) arch_mutex_cpu_relax(); } @@ -404,6 +407,7 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) * * *,x,y -> *,0,0 */ +retry_queue_wait: while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_PENDING_MASK) arch_mutex_cpu_relax(); @@ -420,12 +424,20 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) */ for (;;) { if (val != tail) { - get_qlock(lock); - break; + /* + * The get_qlock function will only failed if the + * lock was stolen. + */ + if (get_qlock(lock)) + break; + else + goto retry_queue_wait; } old = atomic_cmpxchg(&lock->val, val, _Q_LOCKED_VAL); if (old == val) goto release; /* No contention */ + else if (old & _Q_LOCKED_MASK) + goto retry_queue_wait; val = old; } @@ -436,7 +448,7 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) while (!(next = (struct qnode *)ACCESS_ONCE(node->mcs.next))) arch_mutex_cpu_relax(); - arch_mcs_spin_unlock_contended(&next->mcs.locked); + arch_mcs_spin_unlock_contended(&next->qhead); release: /* -- 1.7.1 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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