diff options
author | Will Deacon <will.deacon@arm.com> | 2013-10-09 14:54:26 (GMT) |
---|---|---|
committer | Catalin Marinas <catalin.marinas@arm.com> | 2013-10-24 14:46:33 (GMT) |
commit | 52ea2a560a9dba57fe5fd6b4726b1089751accf2 (patch) | |
tree | 5cd58ed43397b9f52fa3d63a11bc272f3a834967 /arch/arm64/include | |
parent | e29a074b44a9110c567fc31cdb12928f8eca7c79 (diff) | |
download | linux-52ea2a560a9dba57fe5fd6b4726b1089751accf2.tar.xz |
arm64: locks: introduce ticket-based spinlock implementation
This patch introduces a ticket lock implementation for arm64, along the
same lines as the implementation for arch/arm/.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64/include')
-rw-r--r-- | arch/arm64/include/asm/spinlock.h | 79 | ||||
-rw-r--r-- | arch/arm64/include/asm/spinlock_types.h | 10 |
2 files changed, 58 insertions, 31 deletions
diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index 0defa07..525dd53 100644 --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -22,17 +22,10 @@ /* * Spinlock implementation. * - * The old value is read exclusively and the new one, if unlocked, is written - * exclusively. In case of failure, the loop is restarted. - * * The memory barriers are implicit with the load-acquire and store-release * instructions. - * - * Unlocked value: 0 - * Locked value: 1 */ -#define arch_spin_is_locked(x) ((x)->lock != 0) #define arch_spin_unlock_wait(lock) \ do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0) @@ -41,32 +34,51 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) { unsigned int tmp; + arch_spinlock_t lockval, newval; asm volatile( - " sevl\n" - "1: wfe\n" - "2: ldaxr %w0, %1\n" - " cbnz %w0, 1b\n" - " stxr %w0, %w2, %1\n" - " cbnz %w0, 2b\n" - : "=&r" (tmp), "+Q" (lock->lock) - : "r" (1) - : "cc", "memory"); + /* Atomically increment the next ticket. */ +" prfm pstl1strm, %3\n" +"1: ldaxr %w0, %3\n" +" add %w1, %w0, %w5\n" +" stxr %w2, %w1, %3\n" +" cbnz %w2, 1b\n" + /* 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( - "2: ldaxr %w0, %1\n" - " cbnz %w0, 1f\n" - " stxr %w0, %w2, %1\n" - " cbnz %w0, 2b\n" - "1:\n" - : "=&r" (tmp), "+Q" (lock->lock) - : "r" (1) - : "cc", "memory"); +" 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:" + : "=&r" (lockval), "=&r" (tmp), "+Q" (*lock) + : "I" (1 << TICKET_SHIFT) + : "memory"); return !tmp; } @@ -74,9 +86,24 @@ static inline int arch_spin_trylock(arch_spinlock_t *lock) static inline void arch_spin_unlock(arch_spinlock_t *lock) { asm volatile( - " stlr %w1, %0\n" - : "=Q" (lock->lock) : "r" (0) : "memory"); +" stlrh %w1, %0\n" + : "=Q" (lock->owner) + : "r" (lock->owner + 1) + : "memory"); +} + +static inline int arch_spin_is_locked(arch_spinlock_t *lock) +{ + arch_spinlock_t lockval = ACCESS_ONCE(*lock); + return lockval.owner != lockval.next; +} + +static inline int arch_spin_is_contended(arch_spinlock_t *lock) +{ + arch_spinlock_t lockval = ACCESS_ONCE(*lock); + return (lockval.next - lockval.owner) > 1; } +#define arch_spin_is_contended arch_spin_is_contended /* * Write lock implementation. diff --git a/arch/arm64/include/asm/spinlock_types.h b/arch/arm64/include/asm/spinlock_types.h index 9a49434..8769275 100644 --- a/arch/arm64/include/asm/spinlock_types.h +++ b/arch/arm64/include/asm/spinlock_types.h @@ -20,14 +20,14 @@ # error "please don't include this file directly" #endif -/* We only require natural alignment for exclusive accesses. */ -#define __lock_aligned +#define TICKET_SHIFT 16 typedef struct { - volatile unsigned int lock; -} arch_spinlock_t; + u16 owner; + u16 next; +} __aligned(4) arch_spinlock_t; -#define __ARCH_SPIN_LOCK_UNLOCKED { 0 } +#define __ARCH_SPIN_LOCK_UNLOCKED { 0 , 0 } typedef struct { volatile unsigned int lock; |