From 66c407545f4ca32d739637cc489cac9551ddea98 Mon Sep 17 00:00:00 2001 From: Greg Burd Date: Fri, 20 Mar 2026 15:55:39 -0400 Subject: [PATCH v3 5/5] Spin delay on Windows ARM64/MSVC should use __isb(_ARM64_BARRIER_SY) On Windows AArch64 research indicates that ISB performs better than the YIELD hint instruction at scale. This matches the pattern used for __aarch64__ with GCC/Clang, which uses the ISB instruction. Discussion: https://postgr.es/m/1c2a29b8-5b1e-44f7-a871-71ec5fefc120%40app.fastmail.com --- src/include/port/spin_delay.h | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/src/include/port/spin_delay.h b/src/include/port/spin_delay.h index be475f5853c..a3634290cbf 100644 --- a/src/include/port/spin_delay.h +++ b/src/include/port/spin_delay.h @@ -67,14 +67,20 @@ pg_spin_delay(void) #ifdef _MSC_VER +#if defined(_M_ARM64) || defined(_M_ARM64EC) /* - * If using Visual C++ on Win64, inline assembly is unavailable. Use a - * _mm_pause intrinsic instead of rep nop. + * Research indicates ISB is better than __yield() on AArch64. See + * https://postgr.es/m/1c2a29b8-5b1e-44f7-a871-71ec5fefc120%40app.fastmail.com. + */ + __isb(_ARM64_BARRIER_SY); +#elif defined(_WIN64) + /* + * x86_64: inline assembly is unavailable. Use _mm_pause intrinsic + * instead of rep nop. */ -#if defined(_WIN64) _mm_pause(); #else - /* See comment for gcc code. Same code, MASM syntax */ + /* x86 32-bit: Use inline assembly. Same code as gcc, MASM syntax */ __asm rep nop; #endif #endif /* _MSC_VER */ -- 2.51.2