From c11090474d70590170cf5fa6afe85864ab494b37 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@arm.com>
Date: Tue, 13 Mar 2018 20:45:45 +0000
Subject: [PATCH] arm64: locking: Replace ticket lock implementation with
qspinlock
It's fair to say that our ticket lock has served us well over time, but
it's time to bite the bullet and start using the generic qspinlock code
so we can make use of explicit MCS queuing and potentially better PV
performance in future.
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/Kbuild | 1 +
arch/arm64/include/asm/spinlock.h | 117 +-----------------------
arch/arm64/include/asm/spinlock_types.h | 17 +---
4 files changed, 4 insertions(+), 132 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 42c090cf02927..facd19625563a 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -44,6 +44,7 @@ config ARM64
select ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE if !PREEMPT
select ARCH_USE_CMPXCHG_LOCKREF
select ARCH_USE_QUEUED_RWLOCKS
+ select ARCH_USE_QUEUED_SPINLOCKS
select ARCH_SUPPORTS_MEMORY_FAILURE
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_SUPPORTS_INT128 if GCC_VERSION >= 50000 || CC_IS_CLANG
diff --git a/arch/arm64/include/asm/Kbuild b/arch/arm64/include/asm/Kbuild
index 3a9b84d39d716..6cd5d77b6b44b 100644
--- a/arch/arm64/include/asm/Kbuild
+++ b/arch/arm64/include/asm/Kbuild
@@ -16,6 +16,7 @@ generic-y += mm-arch-hooks.h
generic-y += msi.h
generic-y += preempt.h
generic-y += qrwlock.h
+generic-y += qspinlock.h
generic-y += rwsem.h
generic-y += segment.h
generic-y += serial.h
diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
index 26c5bd7d88d8d..38116008d18b3 100644
--- a/arch/arm64/include/asm/spinlock.h
+++ b/arch/arm64/include/asm/spinlock.h
@@ -16,123 +16,8 @@
#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H
-#include <asm/lse.h>
-#include <asm/spinlock_types.h>
-#include <asm/processor.h>
-
-/*
- * Spinlock implementation.
- *
- * The memory barriers are implicit with the load-acquire and store-release
- * instructions.
- */
-
-static inline void arch_spin_lock(arch_spinlock_t *lock)
-{
- unsigned int tmp;
- arch_spinlock_t lockval, newval;
-
- asm volatile(
- /* Atomically increment the next ticket. */
- ARM64_LSE_ATOMIC_INSN(
- /* LL/SC */
-" prfm pstl1strm, %3\n"
-"1: ldaxr %w0, %3\n"
-" add %w1, %w0, %w5\n"
-" stxr %w2, %w1, %3\n"
-" cbnz %w2, 1b\n",
- /* LSE atomics */
-" mov %w2, %w5\n"
-" ldadda %w2, %w0, %3\n"
- __nops(3)
- )
-
- /* Did we get the lock? */
-" eor %w1, %w0, %w0, ror #16\n"
-" cbz %w1, 3f\n"
- /*
- * No: spin on the owner. Send a local event to avoid missing an
- * unlock before the exclusive load.
- */
-" sevl\n"
-"2: wfe\n"
-" ldaxrh %w2, %4\n"
-" eor %w1, %w2, %w0, lsr #16\n"
-" cbnz %w1, 2b\n"
- /* We got the lock. Critical section starts here. */
-"3:"
- : "=&r" (lockval), "=&r" (newval), "=&r" (tmp), "+Q" (*lock)
- : "Q" (lock->owner), "I" (1 << TICKET_SHIFT)
- : "memory");
-}
-
-static inline int arch_spin_trylock(arch_spinlock_t *lock)
-{
- unsigned int tmp;
- arch_spinlock_t lockval;
-
- asm volatile(ARM64_LSE_ATOMIC_INSN(
- /* LL/SC */
- " prfm pstl1strm, %2\n"
- "1: ldaxr %w0, %2\n"
- " eor %w1, %w0, %w0, ror #16\n"
- " cbnz %w1, 2f\n"
- " add %w0, %w0, %3\n"
- " stxr %w1, %w0, %2\n"
- " cbnz %w1, 1b\n"
- "2:",
- /* LSE atomics */
- " ldr %w0, %2\n"
- " eor %w1, %w0, %w0, ror #16\n"
- " cbnz %w1, 1f\n"
- " add %w1, %w0, %3\n"
- " casa %w0, %w1, %2\n"
- " sub %w1, %w1, %3\n"
- " eor %w1, %w1, %w0\n"
- "1:")
- : "=&r" (lockval), "=&r" (tmp), "+Q" (*lock)
- : "I" (1 << TICKET_SHIFT)
- : "memory");
-
- return !tmp;
-}
-
-static inline void arch_spin_unlock(arch_spinlock_t *lock)
-{
- unsigned long tmp;
-
- asm volatile(ARM64_LSE_ATOMIC_INSN(
- /* LL/SC */
- " ldrh %w1, %0\n"
- " add %w1, %w1, #1\n"
- " stlrh %w1, %0",
- /* LSE atomics */
- " mov %w1, #1\n"
- " staddlh %w1, %0\n"
- __nops(1))
- : "=Q" (lock->owner), "=&r" (tmp)
- :
- : "memory");
-}
-
-static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
-{
- return lock.owner == lock.next;
-}
-
-static inline int arch_spin_is_locked(arch_spinlock_t *lock)
-{
- return !arch_spin_value_unlocked(READ_ONCE(*lock));
-}
-
-static inline int arch_spin_is_contended(arch_spinlock_t *lock)
-{
- arch_spinlock_t lockval = READ_ONCE(*lock);
- return (lockval.next - lockval.owner) > 1;
-}
-#define arch_spin_is_contended arch_spin_is_contended
-
#include <asm/qrwlock.h>
+#include <asm/qspinlock.h>
/* See include/linux/spinlock.h */
#define smp_mb__after_spinlock() smp_mb()
diff --git a/arch/arm64/include/asm/spinlock_types.h b/arch/arm64/include/asm/spinlock_types.h
index 6b856012c51b9..a157ff465e279 100644
--- a/arch/arm64/include/asm/spinlock_types.h
+++ b/arch/arm64/include/asm/spinlock_types.h
@@ -20,22 +20,7 @@
# error "please don't include this file directly"
#endif
-#include <linux/types.h>
-
-#define TICKET_SHIFT 16
-
-typedef struct {
-#ifdef __AARCH64EB__
- u16 next;
- u16 owner;
-#else
- u16 owner;
- u16 next;
-#endif
-} __aligned(4) arch_spinlock_t;
-
-#define __ARCH_SPIN_LOCK_UNLOCKED { 0 , 0 }
-
+#include <asm-generic/qspinlock_types.h>
#include <asm-generic/qrwlock_types.h>
#endif
--
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