Messages in this thread Patch in this message | | | From | Nicholas Piggin <> | Subject | [PATCH 04/13] locking/qspinlock: move pv lock word helpers into qspinlock.c | Date | Tue, 5 Jul 2022 00:38:11 +1000 |
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There is no real reason not to keep all the bit manipulation together.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- kernel/locking/qspinlock.c | 107 ++++++++++++++++------------ kernel/locking/qspinlock_paravirt.h | 51 ------------- 2 files changed, 63 insertions(+), 95 deletions(-)
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 7360d643de29..8f2173e22479 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -141,7 +141,24 @@ struct qnode *grab_qnode(struct qnode *base, int idx) #define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK) +/** + * set_pending - set the pending bit. + * @lock: Pointer to queued spinlock structure + * + * *,0,* -> *,1,* + * + * The pending bit is used by the queue head vCPU to indicate that it + * is actively spinning on the lock and no lock stealing is allowed. + */ +static __always_inline void set_pending(struct qspinlock *lock) +{ #if _Q_PENDING_BITS == 8 + WRITE_ONCE(lock->pending, 1); +#else + atomic_or(_Q_PENDING_VAL, &lock->val); +#endif +} + /** * clear_pending - clear the pending bit. * @lock: Pointer to queued spinlock structure @@ -150,7 +167,11 @@ struct qnode *grab_qnode(struct qnode *base, int idx) */ static __always_inline void clear_pending(struct qspinlock *lock) { +#if _Q_PENDING_BITS == 8 WRITE_ONCE(lock->pending, 0); +#else + atomic_andnot(_Q_PENDING_VAL, &lock->val); +#endif } /** @@ -163,74 +184,72 @@ static __always_inline void clear_pending(struct qspinlock *lock) */ static __always_inline void clear_pending_set_locked(struct qspinlock *lock) { +#if _Q_PENDING_BITS == 8 WRITE_ONCE(lock->locked_pending, _Q_LOCKED_VAL); +#else + atomic_add(-_Q_PENDING_VAL + _Q_LOCKED_VAL, &lock->val); +#endif } -/* - * xchg_tail - Put in the new queue tail code word & retrieve previous one - * @lock : Pointer to queued spinlock structure - * @tail : The new queue tail code word - * Return: The previous queue tail code word - * - * xchg(lock, tail), which heads an address dependency - * - * p,*,* -> n,*,* ; prev = xchg(lock, node) - */ -static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail) -{ - /* - * We can use relaxed semantics since the caller ensures that the - * MCS node is properly initialized before updating the tail. - */ - return (u32)xchg_relaxed(&lock->tail, - tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET; -} - -#else /* _Q_PENDING_BITS == 8 */ - /** - * clear_pending - clear the pending bit. + * trylock_clear_pending - try to take ownership and clear the pending bit * @lock: Pointer to queued spinlock structure * - * *,1,* -> *,0,* + * 0,1,0 -> 0,0,1 */ -static __always_inline void clear_pending(struct qspinlock *lock) +static __always_inline int trylock_clear_pending(struct qspinlock *lock) { - atomic_andnot(_Q_PENDING_VAL, &lock->val); -} +#if _Q_PENDING_BITS == 8 + return !READ_ONCE(lock->locked) && + (cmpxchg_acquire(&lock->locked_pending, _Q_PENDING_VAL, + _Q_LOCKED_VAL) == _Q_PENDING_VAL); +#else + int val = atomic_read(&lock->val); -/** - * clear_pending_set_locked - take ownership and clear the pending bit. - * @lock: Pointer to queued spinlock structure - * - * *,1,0 -> *,0,1 - */ -static __always_inline void clear_pending_set_locked(struct qspinlock *lock) -{ - atomic_add(-_Q_PENDING_VAL + _Q_LOCKED_VAL, &lock->val); + for (;;) { + int old, new; + + if (val & _Q_LOCKED_MASK) + break; + + /* + * Try to clear pending bit & set locked bit + */ + old = val; + new = (val & ~_Q_PENDING_MASK) | _Q_LOCKED_VAL; + val = atomic_cmpxchg_acquire(&lock->val, old, new); + + if (val == old) + return 1; + } + return 0; +#endif } -/** +/* * xchg_tail - Put in the new queue tail code word & retrieve previous one * @lock : Pointer to queued spinlock structure * @tail : The new queue tail code word * Return: The previous queue tail code word * - * xchg(lock, tail) + * xchg(lock, tail), which heads an address dependency * * p,*,* -> n,*,* ; prev = xchg(lock, node) */ static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail) { + /* + * We can use relaxed semantics since the caller ensures that the + * MCS node is properly initialized before updating the tail. + */ +#if _Q_PENDING_BITS == 8 + return (u32)xchg_relaxed(&lock->tail, + tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET; +#else u32 old, new, val = atomic_read(&lock->val); for (;;) { new = (val & _Q_LOCKED_PENDING_MASK) | tail; - /* - * We can use relaxed semantics since the caller ensures that - * the MCS node is properly initialized before updating the - * tail. - */ old = atomic_cmpxchg_relaxed(&lock->val, val, new); if (old == val) break; @@ -238,8 +257,8 @@ static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail) val = old; } return old; +#endif } -#endif /* _Q_PENDING_BITS == 8 */ /** * queued_fetch_set_pending_acquire - fetch the whole lock value and set pending diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h index cce3d3dde216..97385861adc2 100644 --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -95,57 +95,6 @@ static inline bool pv_hybrid_queued_unfair_trylock(struct qspinlock *lock) return false; } -/* - * The pending bit is used by the queue head vCPU to indicate that it - * is actively spinning on the lock and no lock stealing is allowed. - */ -#if _Q_PENDING_BITS == 8 -static __always_inline void set_pending(struct qspinlock *lock) -{ - WRITE_ONCE(lock->pending, 1); -} - -/* - * The pending bit check in pv_queued_spin_steal_lock() isn't a memory - * barrier. Therefore, an atomic cmpxchg_acquire() is used to acquire the - * lock just to be sure that it will get it. - */ -static __always_inline int trylock_clear_pending(struct qspinlock *lock) -{ - return !READ_ONCE(lock->locked) && - (cmpxchg_acquire(&lock->locked_pending, _Q_PENDING_VAL, - _Q_LOCKED_VAL) == _Q_PENDING_VAL); -} -#else /* _Q_PENDING_BITS == 8 */ -static __always_inline void set_pending(struct qspinlock *lock) -{ - atomic_or(_Q_PENDING_VAL, &lock->val); -} - -static __always_inline int trylock_clear_pending(struct qspinlock *lock) -{ - int val = atomic_read(&lock->val); - - for (;;) { - int old, new; - - if (val & _Q_LOCKED_MASK) - break; - - /* - * Try to clear pending bit & set locked bit - */ - old = val; - new = (val & ~_Q_PENDING_MASK) | _Q_LOCKED_VAL; - val = atomic_cmpxchg_acquire(&lock->val, old, new); - - if (val == old) - return 1; - } - return 0; -} -#endif /* _Q_PENDING_BITS == 8 */ - /* * Lock and MCS node addresses hash table for fast lookup * -- 2.35.1
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