From 3d0b4b1068018f624d5ef7c9f90b536ed58345b5 Mon Sep 17 00:00:00 2001 From: Nathan Bossart Date: Fri, 10 Jan 2025 13:18:04 -0600 Subject: [PATCH] Use a non-locking initial test in TAS_SPIN on AArch64. Our testing showed that this is helpful at sufficiently high contention levels and doesn't hurt performance on smaller machines. The new TAS_SPIN macro for AArch64 is identical to the ones added for PPC and x86_64 (see commits bc2a050d40 and b03d196be0). Reported-by: Salvatore Dipietro Reviewed-by: Jingtang Zhang, Andres Freund Tested-by: Tom Lane Discussion: https://postgr.es/m/ZxgDEb_VpWyNZKB_%40nathan --- src/include/storage/s_lock.h | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h index 516fffc53ab..2f73f9fcf57 100644 --- a/src/include/storage/s_lock.h +++ b/src/include/storage/s_lock.h @@ -263,18 +263,24 @@ tas(volatile slock_t *lock) #define S_UNLOCK(lock) __sync_lock_release(lock) -/* - * Using an ISB instruction to delay in spinlock loops appears beneficial on - * high-core-count ARM64 processors. It seems mostly a wash for smaller gear, - * and ISB doesn't exist at all on pre-v7 ARM chips. - */ #if defined(__aarch64__) +/* + * On ARM64, it's a win to use a non-locking test before the TAS proper. It + * may be a win on 32-bit ARM, too, but nobody's tested it yet. + */ +#define TAS_SPIN(lock) (*(lock) ? 1 : TAS(lock)) + #define SPIN_DELAY() spin_delay() static __inline__ void spin_delay(void) { + /* + * Using an ISB instruction to delay in spinlock loops appears beneficial + * on high-core-count ARM64 processors. It seems mostly a wash for smaller + * gear, and ISB doesn't exist at all on pre-v7 ARM chips. + */ __asm__ __volatile__( " isb; \n"); }