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unix: Improve uv__cpu_relax() on Arm

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The AArch64 YIELD instruction affects processors that support
symmetric multithreading, while on other implementations (which
are the majority on the market) it is equivalent to NOP, thus
failing to achieve the desired delay effect inside uv__async_spin().
Instead, use the ISB instruction, following one of Arm's
recommendations [1].

[1] https://community.arm.com/arm-community-blogs/b/architectures-and-processors-blog/posts/multi-threaded-applications-arm

Signed-off-by: Anton Kirilov <anton.kirilov@arm.com>
This commit is contained in:
Anton Kirilov 2025-08-14 16:00:48 +00:00
parent 07c8a3c4ca
commit 9c11d9ae4b
1 changed files with 1 additions and 1 deletions
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src/unix/async.c
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@ -409,7 +409,7 @@ static void uv__cpu_relax(void) {
#if defined(__i386__) || defined(__x86_64__)
__asm__ __volatile__ ("rep; nop" ::: "memory"); /* a.k.a. PAUSE */
#elif (defined(__arm__) && __ARM_ARCH >= 7) || defined(__aarch64__)
__asm__ __volatile__ ("yield" ::: "memory");
__asm__ __volatile__ ("isb" ::: "memory");
#elif (defined(__ppc__) || defined(__ppc64__)) && defined(__APPLE__)
__asm volatile ("" : : : "memory");
#elif !defined(__APPLE__) && (defined(__powerpc64__) || defined(__ppc64__) || defined(__PPC64__))