diff options
Diffstat (limited to 'lib/locks/exclusive/aarch64/spinlock.S')
-rw-r--r-- | lib/locks/exclusive/aarch64/spinlock.S | 53 |
1 files changed, 18 insertions, 35 deletions
diff --git a/lib/locks/exclusive/aarch64/spinlock.S b/lib/locks/exclusive/aarch64/spinlock.S index d0569f1c..e941b8a3 100644 --- a/lib/locks/exclusive/aarch64/spinlock.S +++ b/lib/locks/exclusive/aarch64/spinlock.S @@ -9,56 +9,38 @@ .globl spin_lock .globl spin_unlock -#if ARM_ARCH_AT_LEAST(8, 1) +#if USE_SPINLOCK_CAS +#if !ARM_ARCH_AT_LEAST(8, 1) +#error USE_SPINLOCK_CAS option requires at least an ARMv8.1 platform +#endif /* * When compiled for ARMv8.1 or later, choose spin locks based on Compare and * Swap instruction. */ -# define USE_CAS 1 - -/* - * Lock contenders using CAS, upon failing to acquire the lock, wait with the - * monitor in open state. Therefore, a normal store upon unlocking won't - * generate an SEV. Use explicit SEV instruction with CAS unlock. - */ -# define COND_SEV() sev - -#else - -# define USE_CAS 0 - -/* - * Lock contenders using exclusive pairs, upon failing to acquire the lock, wait - * with the monitor in exclusive state. A normal store upon unlocking will - * implicitly generate an envent; so, no explicit SEV with unlock is required. - */ -# define COND_SEV() - -#endif - -#if USE_CAS /* * Acquire lock using Compare and Swap instruction. * - * Compare for 0 with acquire semantics, and swap 1. Wait until CAS returns - * 0. + * Compare for 0 with acquire semantics, and swap 1. If failed to acquire, use + * load exclusive semantics to monitor the address and enter WFE. * * void spin_lock(spinlock_t *lock); */ func spin_lock mov w2, #1 - sevl -1: +1: mov w1, wzr +2: casa w1, w2, [x0] + cbz w1, 3f + ldxr w1, [x0] + cbz w1, 2b wfe - mov w1, wzr - casa w1, w2, [x0] - cbnz w1, 1b + b 1b +3: ret endfunc spin_lock -#else /* !USE_CAS */ +#else /* !USE_SPINLOCK_CAS */ /* * Acquire lock using load-/store-exclusive instruction pair. @@ -76,17 +58,18 @@ l2: ldaxr w1, [x0] ret endfunc spin_lock -#endif /* USE_CAS */ +#endif /* USE_SPINLOCK_CAS */ /* * Release lock previously acquired by spin_lock. * - * Unconditionally write 0, and conditionally generate an event. + * Use store-release to unconditionally clear the spinlock variable. + * Store operation generates an event to all cores waiting in WFE + * when address is monitored by the global monitor. * * void spin_unlock(spinlock_t *lock); */ func spin_unlock stlr wzr, [x0] - COND_SEV() ret endfunc spin_unlock |