[PATCH v3] Cygwin: implement spinlock pause for AArch64

[Jeremy Drake]

On Thu, 19 Jun 2025, Radek Barton wrote:

> Hello.
>
> Sending new version with Signed-off-by header.
>
> Radek
>
> ---
> From 2726b40ae1b41586e410105d5fd5149f8e7f6b92 Mon Sep 17 00:00:00 2001
> From: =?UTF-8?q?Radek=20Barto=C5=88?= <radek.barton@microsoft.com>
> Date: Thu, 5 Jun 2025 12:41:37 +0200
> Subject: [PATCH v3] Cygwin: implement spinlock pause for AArch64
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
>
> Signed-off-by: Radek Bartoň <radek.barton@microsoft.com>
> ---
>  winsup/cygwin/local_includes/cygtls.h           | 5 ++++-
>  winsup/cygwin/thread.cc                         | 5 +++++
>  winsup/testsuite/winsup.api/pthread/cpu_relax.h | 3 ++-
>  3 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/winsup/cygwin/local_includes/cygtls.h b/winsup/cygwin/local_includes/cygtls.h
> index 615361d3f..31cadd51a 100644
> --- a/winsup/cygwin/local_includes/cygtls.h
> +++ b/winsup/cygwin/local_includes/cygtls.h
> @@ -243,8 +243,11 @@ public: /* Do NOT remove this public: line, it's a marker for gentls_offsets. */
>    {
>      while (InterlockedExchange (&stacklock, 1))
>        {
> -#ifdef __x86_64__
> +#if defined(__x86_64__)
>       __asm__ ("pause");
> +#elif defined(__aarch64__)
> +     __asm__ ("dmb ishst\n"
> +                 "yield");
>  #else
>  #error unimplemented for this target
>  #endif
> diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
> index fea6079b8..510e2be93 100644
> --- a/winsup/cygwin/thread.cc
> +++ b/winsup/cygwin/thread.cc
> @@ -1968,7 +1968,12 @@ pthread_spinlock::lock ()
>        else if (spins < FAST_SPINS_LIMIT)
>          {
>            ++spins;
> +#if defined(__x86_64__)
>            __asm__ volatile ("pause":::);
> +#elif defined(__aarch64__)
> +          __asm__ volatile ("dmb ishst\n"
> +                            "yield":::);
> +#endif
>          }
>        else
>       {
> diff --git a/winsup/testsuite/winsup.api/pthread/cpu_relax.h b/winsup/testsuite/winsup.api/pthread/cpu_relax.h
> index 1936dc5f4..71cec0b2b 100644
> --- a/winsup/testsuite/winsup.api/pthread/cpu_relax.h
> +++ b/winsup/testsuite/winsup.api/pthread/cpu_relax.h
> @@ -4,7 +4,8 @@
>  #if defined(__x86_64__) || defined(__i386__)  // Check for x86 architectures
>     #define CPU_RELAX() __asm__ volatile ("pause" :::)
>  #elif defined(__aarch64__) || defined(__arm__)  // Check for ARM architectures
> -   #define CPU_RELAX() __asm__ volatile ("yield" :::)
> +   #define CPU_RELAX() __asm__ volatile ("dmb ishst \
> +                                          yield" :::)
>  #else
>     #error unimplemented for this target
>  #endif
> --
> 2.49.0.vfs.0.4
>

Pushed, thanks