[PATCH] Implements SPIN_LOCK on ARM

From 89b310c5192e75cfd1844c324cb8a92e2bc414c8 Mon Sep 17 00:00:00 2001
From: David Carlier <devnexen@gmail.com>
Date: Fri, 18 Dec 2020 21:48:35 +0000
Subject: [PATCH] Implements SPIN_LOCK macro for ARM.

using yield instruction which is the x86's "pause" equivalent.

Signed-off-by: David Carlier <devnexen@gmail.com>
---
 src/include/storage/s_lock.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h
index 31a5ca6fb3..b4d1d1f515 100644
--- a/src/include/storage/s_lock.h
+++ b/src/include/storage/s_lock.h
@@ -336,6 +336,29 @@ tas(volatile slock_t *lock)
 
 #define S_UNLOCK(lock) __sync_lock_release(lock)
 
+#if defined(__aarch64__) || __ARM_ARCH__ >= 7
+
+#define SPIN_LOCK spin_delay
+
+static __inline__ void
+spin_delay(void)
+{
+	/*
+	 * With spin locks, the yield hint
+	 * improves CPU usage and performance
+	 * on ARM hardwares implemented on 64 bits
+	 * but is a NOP on ARM11 for example thus
+	 * enabling this instruction when useful.
+	 */
+	__asm__ __volatile__(
+		"       yield     \n"
+:
+:
+:		"memory");
+
+}
+
+#endif   /* __aarch64__ || __ARM_ARCH__ >= 7 */
 #endif	 /* HAVE_GCC__SYNC_INT32_TAS */
 #endif	 /* __arm__ || __arm || __aarch64__ || __aarch64 */
 
-- 
2.20.1