x86, locking/spinlocks: Remove ticket (spin)lock implementation

We've unconditionally used the queued spinlock for many releases now. Its time to remove the old ticket lock code. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Waiman Long <waiman.long@hpe.com> Cc: Waiman.Long@hpe.com Cc: david.vrabel@citrix.com Cc: dhowells@redhat.com Cc: pbonzini@redhat.com Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/20160518184302.GO3193@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
mariux64 · Sep 30, 2016 · cfd8983 · cfd8983
1 parent 0b429e1
commit cfd8983
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Showing 10 changed files with 6 additions and 719 deletions.
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
@@ -705,7 +705,6 @@ config PARAVIRT_DEBUG
 config PARAVIRT_SPINLOCKS
 	bool "Paravirtualization layer for spinlocks"
 	depends on PARAVIRT && SMP
-	select UNINLINE_SPIN_UNLOCK if !QUEUED_SPINLOCKS
 	---help---
 	  Paravirtualized spinlocks allow a pvops backend to replace the
 	  spinlock implementation with something virtualization-friendly
@@ -718,7 +717,7 @@ config PARAVIRT_SPINLOCKS
 
 config QUEUED_LOCK_STAT
 	bool "Paravirt queued spinlock statistics"
-	depends on PARAVIRT_SPINLOCKS && DEBUG_FS && QUEUED_SPINLOCKS
+	depends on PARAVIRT_SPINLOCKS && DEBUG_FS
 	---help---
 	  Enable the collection of statistical data on the slowpath
 	  behavior of paravirtualized queued spinlocks and report

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
@@ -661,8 +661,6 @@ static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx,
 
 #if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT_SPINLOCKS)
 
-#ifdef CONFIG_QUEUED_SPINLOCKS
-
 static __always_inline void pv_queued_spin_lock_slowpath(struct qspinlock *lock,
 							u32 val)
 {
@@ -684,22 +682,6 @@ static __always_inline void pv_kick(int cpu)
 	PVOP_VCALL1(pv_lock_ops.kick, cpu);
 }
 
-#else /* !CONFIG_QUEUED_SPINLOCKS */
-
-static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
-							__ticket_t ticket)
-{
-	PVOP_VCALLEE2(pv_lock_ops.lock_spinning, lock, ticket);
-}
-
-static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
-							__ticket_t ticket)
-{
-	PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket);
-}
-
-#endif /* CONFIG_QUEUED_SPINLOCKS */
-
 #endif /* SMP && PARAVIRT_SPINLOCKS */
 
 #ifdef CONFIG_X86_32

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
@@ -301,23 +301,16 @@ struct pv_mmu_ops {
 struct arch_spinlock;
 #ifdef CONFIG_SMP
 #include <asm/spinlock_types.h>
-#else
-typedef u16 __ticket_t;
 #endif
 
 struct qspinlock;
 
 struct pv_lock_ops {
-#ifdef CONFIG_QUEUED_SPINLOCKS
 	void (*queued_spin_lock_slowpath)(struct qspinlock *lock, u32 val);
 	struct paravirt_callee_save queued_spin_unlock;
 
 	void (*wait)(u8 *ptr, u8 val);
 	void (*kick)(int cpu);
-#else /* !CONFIG_QUEUED_SPINLOCKS */
-	struct paravirt_callee_save lock_spinning;
-	void (*unlock_kick)(struct arch_spinlock *lock, __ticket_t ticket);
-#endif /* !CONFIG_QUEUED_SPINLOCKS */
 };
 
 /* This contains all the paravirt structures: we get a convenient

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
@@ -20,187 +20,13 @@
  * (the type definitions are in asm/spinlock_types.h)
  */
 
-#ifdef CONFIG_X86_32
-# define LOCK_PTR_REG "a"
-#else
-# define LOCK_PTR_REG "D"
-#endif
-
-#if defined(CONFIG_X86_32) && (defined(CONFIG_X86_PPRO_FENCE))
-/*
- * On PPro SMP, we use a locked operation to unlock
- * (PPro errata 66, 92)
- */
-# define UNLOCK_LOCK_PREFIX LOCK_PREFIX
-#else
-# define UNLOCK_LOCK_PREFIX
-#endif
-
 /* How long a lock should spin before we consider blocking */
 #define SPIN_THRESHOLD	(1 << 15)
 
 extern struct static_key paravirt_ticketlocks_enabled;
 static __always_inline bool static_key_false(struct static_key *key);
 
-#ifdef CONFIG_QUEUED_SPINLOCKS
 #include <asm/qspinlock.h>
-#else
-
-#ifdef CONFIG_PARAVIRT_SPINLOCKS
-
-static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
-{
-	set_bit(0, (volatile unsigned long *)&lock->tickets.head);
-}
-
-#else  /* !CONFIG_PARAVIRT_SPINLOCKS */
-static __always_inline void __ticket_lock_spinning(arch_spinlock_t *lock,
-							__ticket_t ticket)
-{
-}
-static inline void __ticket_unlock_kick(arch_spinlock_t *lock,
-							__ticket_t ticket)
-{
-}
-
-#endif /* CONFIG_PARAVIRT_SPINLOCKS */
-static inline int  __tickets_equal(__ticket_t one, __ticket_t two)
-{
-	return !((one ^ two) & ~TICKET_SLOWPATH_FLAG);
-}
-
-static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
-							__ticket_t head)
-{
-	if (head & TICKET_SLOWPATH_FLAG) {
-		arch_spinlock_t old, new;
-
-		old.tickets.head = head;
-		new.tickets.head = head & ~TICKET_SLOWPATH_FLAG;
-		old.tickets.tail = new.tickets.head + TICKET_LOCK_INC;
-		new.tickets.tail = old.tickets.tail;
-
-		/* try to clear slowpath flag when there are no contenders */
-		cmpxchg(&lock->head_tail, old.head_tail, new.head_tail);
-	}
-}
-
-static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
-{
-	return __tickets_equal(lock.tickets.head, lock.tickets.tail);
-}
-
-/*
- * Ticket locks are conceptually two parts, one indicating the current head of
- * the queue, and the other indicating the current tail. The lock is acquired
- * by atomically noting the tail and incrementing it by one (thus adding
- * ourself to the queue and noting our position), then waiting until the head
- * becomes equal to the the initial value of the tail.
- *
- * We use an xadd covering *both* parts of the lock, to increment the tail and
- * also load the position of the head, which takes care of memory ordering
- * issues and should be optimal for the uncontended case. Note the tail must be
- * in the high part, because a wide xadd increment of the low part would carry
- * up and contaminate the high part.
- */
-static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
-{
-	register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
-
-	inc = xadd(&lock->tickets, inc);
-	if (likely(inc.head == inc.tail))
-		goto out;
-
-	for (;;) {
-		unsigned count = SPIN_THRESHOLD;
-
-		do {
-			inc.head = READ_ONCE(lock->tickets.head);
-			if (__tickets_equal(inc.head, inc.tail))
-				goto clear_slowpath;
-			cpu_relax();
-		} while (--count);
-		__ticket_lock_spinning(lock, inc.tail);
-	}
-clear_slowpath:
-	__ticket_check_and_clear_slowpath(lock, inc.head);
-out:
-	barrier();	/* make sure nothing creeps before the lock is taken */
-}
-
-static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
-{
-	arch_spinlock_t old, new;
-
-	old.tickets = READ_ONCE(lock->tickets);
-	if (!__tickets_equal(old.tickets.head, old.tickets.tail))
-		return 0;
-
-	new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
-	new.head_tail &= ~TICKET_SLOWPATH_FLAG;
-
-	/* cmpxchg is a full barrier, so nothing can move before it */
-	return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail;
-}
-
-static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
-{
-	if (TICKET_SLOWPATH_FLAG &&
-		static_key_false(&paravirt_ticketlocks_enabled)) {
-		__ticket_t head;
-
-		BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
-
-		head = xadd(&lock->tickets.head, TICKET_LOCK_INC);
-
-		if (unlikely(head & TICKET_SLOWPATH_FLAG)) {
-			head &= ~TICKET_SLOWPATH_FLAG;
-			__ticket_unlock_kick(lock, (head + TICKET_LOCK_INC));
-		}
-	} else
-		__add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
-}
-
-static inline int arch_spin_is_locked(arch_spinlock_t *lock)
-{
-	struct __raw_tickets tmp = READ_ONCE(lock->tickets);
-
-	return !__tickets_equal(tmp.tail, tmp.head);
-}
-
-static inline int arch_spin_is_contended(arch_spinlock_t *lock)
-{
-	struct __raw_tickets tmp = READ_ONCE(lock->tickets);
-
-	tmp.head &= ~TICKET_SLOWPATH_FLAG;
-	return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
-}
-#define arch_spin_is_contended	arch_spin_is_contended
-
-static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
-						  unsigned long flags)
-{
-	arch_spin_lock(lock);
-}
-
-static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
-{
-	__ticket_t head = READ_ONCE(lock->tickets.head);
-
-	for (;;) {
-		struct __raw_tickets tmp = READ_ONCE(lock->tickets);
-		/*
-		 * We need to check "unlocked" in a loop, tmp.head == head
-		 * can be false positive because of overflow.
-		 */
-		if (__tickets_equal(tmp.head, tmp.tail) ||
-				!__tickets_equal(tmp.head, head))
-			break;
-
-		cpu_relax();
-	}
-}
-#endif /* CONFIG_QUEUED_SPINLOCKS */
 
 /*
  * Read-write spinlocks, allowing multiple readers

diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
@@ -23,20 +23,7 @@ typedef u32 __ticketpair_t;
 
 #define TICKET_SHIFT	(sizeof(__ticket_t) * 8)
 
-#ifdef CONFIG_QUEUED_SPINLOCKS
 #include <asm-generic/qspinlock_types.h>
-#else
-typedef struct arch_spinlock {
-	union {
-		__ticketpair_t head_tail;
-		struct __raw_tickets {
-			__ticket_t head, tail;
-		} tickets;
-	};
-} arch_spinlock_t;
-
-#define __ARCH_SPIN_LOCK_UNLOCKED	{ { 0 } }
-#endif /* CONFIG_QUEUED_SPINLOCKS */
 
 #include <asm-generic/qrwlock_types.h>