1 files changed, 93 insertions, 0 deletions
diff --git a/include/my_cpu.h b/include/my_cpu.h
index ebabe6c7202..aff92d22131 100644
--- a/include/my_cpu.h
+++ b/include/my_cpu.h
@@ -1,3 +1,5 @@
+#ifndef MY_CPU_INCLUDED
+#define MY_CPU_INCLUDED
 /* Copyright (c) 2013, MariaDB foundation Ab and SkySQL
 
    This program is free software; you can redistribute it and/or modify
@@ -42,3 +44,94 @@
 #define HMT_medium_high()
 #define HMT_high()
 #endif
+
+#if defined __i386__ || defined __x86_64__ || defined _WIN32
+# define HAVE_PAUSE_INSTRUCTION /* added in Intel Pentium 4 */
+#endif
+
+#ifdef _WIN32
+#elif defined HAVE_PAUSE_INSTRUCTION
+#elif defined(_ARCH_PWR8)
+#else
+# include "my_global.h"
+# include "my_atomic.h"
+#endif
+
+static inline void MY_RELAX_CPU(void)
+{
+#ifdef _WIN32
+  /*
+    In the Win32 API, the x86 PAUSE instruction is executed by calling
+    the YieldProcessor macro defined in WinNT.h. It is a CPU architecture-
+    independent way by using YieldProcessor.
+  */
+  YieldProcessor();
+#elif defined HAVE_PAUSE_INSTRUCTION
+  /*
+    According to the gcc info page, asm volatile means that the
+    instruction has important side-effects and must not be removed.
+    Also asm volatile may trigger a memory barrier (spilling all registers
+    to memory).
+  */
+#ifdef __SUNPRO_CC
+  asm ("pause" );
+#else
+  __asm__ __volatile__ ("pause");
+#endif
+#elif defined(_ARCH_PWR8)
+  __ppc_get_timebase();
+#else
+  int32 var, oldval = 0;
+  my_atomic_cas32_strong_explicit(&var, &oldval, 1, MY_MEMORY_ORDER_RELAXED,
+                                  MY_MEMORY_ORDER_RELAXED);
+#endif
+}
+
+
+#ifdef HAVE_PAUSE_INSTRUCTION
+# ifdef __cplusplus
+extern "C" {
+# endif
+extern unsigned my_cpu_relax_multiplier;
+void my_cpu_init(void);
+# ifdef __cplusplus
+}
+# endif
+#else
+# define my_cpu_relax_multiplier 200
+# define my_cpu_init() /* nothing */
+#endif
+
+/*
+  LF_BACKOFF should be used to improve performance on hyperthreaded CPUs. Intel
+  recommends to use it in spin loops also on non-HT machines to reduce power
+  consumption (see e.g http://softwarecommunity.intel.com/articles/eng/2004.htm)
+
+  Running benchmarks for spinlocks implemented with InterlockedCompareExchange
+  and YieldProcessor shows that much better performance is achieved by calling
+  YieldProcessor in a loop - that is, yielding longer. On Intel boxes setting
+  loop count in the range 200-300 brought best results.
+*/
+
+static inline int LF_BACKOFF(void)
+{
+  unsigned i= my_cpu_relax_multiplier;
+  while (i--)
+    MY_RELAX_CPU();
+  return 1;
+}
+/**
+  Run a delay loop while waiting for a shared resource to be released.
+  @param delay originally, roughly microseconds on 100 MHz Intel Pentium
+*/
+
+static inline void ut_delay(unsigned delay)
+{
+  unsigned i= my_cpu_relax_multiplier / 4 * delay;
+  HMT_low();
+  while (i--)
+    MY_RELAX_CPU();
+  HMT_medium();
+}
+
+#endif