[PATCH v2 03/17] powerpc/qspinlock: use a half-word store to unlock to avoid larx/stcx.
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2022-11-14 02:36:28
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
The first 16 bits of the lock are only modified by the owner, and other modifications always use atomic operations on the entire 32 bits, so unlocks can use plain stores on the 16 bits. This is the same kind of optimisation done by core qspinlock code. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/include/asm/qspinlock.h | 6 +----- arch/powerpc/include/asm/qspinlock_types.h | 19 +++++++++++++++++-- 2 files changed, 18 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/include/asm/qspinlock.h b/arch/powerpc/include/asm/qspinlock.h
index 300c7d2ebe2e..7bc254c55705 100644
--- a/arch/powerpc/include/asm/qspinlock.h
+++ b/arch/powerpc/include/asm/qspinlock.h@@ -36,11 +36,7 @@ static __always_inline void queued_spin_lock(struct qspinlock *lock) static inline void queued_spin_unlock(struct qspinlock *lock) { - for (;;) { - int val = atomic_read(&lock->val); - if (atomic_cmpxchg_release(&lock->val, val, val & ~_Q_LOCKED_VAL) == val) - return; - } + smp_store_release(&lock->locked, 0); } #define arch_spin_is_locked(l) queued_spin_is_locked(l)
diff --git a/arch/powerpc/include/asm/qspinlock_types.h b/arch/powerpc/include/asm/qspinlock_types.h
index 9630e714c70d..3425dab42576 100644
--- a/arch/powerpc/include/asm/qspinlock_types.h
+++ b/arch/powerpc/include/asm/qspinlock_types.h@@ -3,12 +3,27 @@ #define _ASM_POWERPC_QSPINLOCK_TYPES_H #include <linux/types.h> +#include <asm/byteorder.h> typedef struct qspinlock { - atomic_t val; + union { + atomic_t val; + +#ifdef __LITTLE_ENDIAN + struct { + u16 locked; + u8 reserved[2]; + }; +#else + struct { + u8 reserved[2]; + u16 locked; + }; +#endif + }; } arch_spinlock_t; -#define __ARCH_SPIN_LOCK_UNLOCKED { .val = ATOMIC_INIT(0) } +#define __ARCH_SPIN_LOCK_UNLOCKED { { .val = ATOMIC_INIT(0) } } /* * Bitfields in the atomic value:
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2.37.2