branches/zip:

Use PAUSE instruction inside spinloop if it is available.

The patch was originally developed by Mikael Ronstrom <mikael@mysql.com>
and can be found here:
http://bazaar.launchpad.net/%7Emysql/mysql-server/mysql-5.4/revision/2768
http://bazaar.launchpad.net/%7Emysql/mysql-server/mysql-5.4/revision/2771
http://bazaar.launchpad.net/%7Emysql/mysql-server/mysql-5.4/revision/2772
http://bazaar.launchpad.net/%7Emysql/mysql-server/mysql-5.4/revision/2774
http://bazaar.launchpad.net/%7Emysql/mysql-server/mysql-5.4/revision/2777
http://bazaar.launchpad.net/%7Emysql/mysql-server/mysql-5.4/revision/2799
http://bazaar.launchpad.net/%7Emysql/mysql-server/mysql-5.4/revision/2800

Approved by:	Heikki (rb://137)

ChangeLog

+2009-07-02	The InnoDB Team
+
+	* include/ut0ut.h, plug.in, ut/ut0ut.c:
+	Use the PAUSE instruction inside the spinloop if it is available,
+	Thanks to Mikael Ronstrom <mikael@mysql.com>.
+
 2009-06-29	The InnoDB Team
 
 	* handler/ha_innodb.cc, mysql-test/innodb_file_format.test,

include/ut0ut.h

@@ -40,6 +40,21 @@ Created 1/20/1994 Heikki Tuuri
 /** Time stamp */
 typedef time_t	ib_time_t;
 
+#if defined(IB_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). */
+#  define UT_RELAX_CPU() __asm__ __volatile__ ("pause")
+#elif defined(HAVE_ATOMIC_BUILTINS)
+#  define UT_RELAX_CPU() do { \
+     volatile lint	volatile_var; \
+     os_compare_and_swap_lint(&volatile_var, 0, 1); \
+   } while (0)
+#else
+#  define UT_RELAX_CPU() ((void)0) /* avoid warning for an empty statement */
+#endif
+
 /*********************************************************************//**
 Delays execution for at most max_wait_us microseconds or returns earlier
 if cond becomes true.

plug.in

@@ -123,6 +123,28 @@ MYSQL_PLUGIN_ACTIONS(innobase,  [
             ])
         ])
     ])
+  # Check for x86 PAUSE instruction
+  AC_MSG_CHECKING("for x86 PAUSE instruction")
+  # We have to actually try running the test program, because of a bug
+  # in Solaris on x86_64, where it wrongly reports that PAUSE is not
+  # supported when trying to run an application. See
+  # http://bugs.opensolaris.org/bugdatabase/printableBug.do?bug_id=6478684
+  # We use ib_ prefix to avoid collisoins if this code is added to
+  # mysql's configure.in.
+  AC_TRY_RUN([
+      int main() {
+        __asm__ __volatile__ ("pause");
+        return(0);
+      }
+    ],
+    [ib_x86_pause_exists=yes],
+    [ib_x86_pause_exists=no],
+    [ib_x86_pause_exists=no]  # Cross-compile, assume no PAUSE instruction
+  )
+  if test "$ib_x86_pause_exists" = "yes"
+  then
+    AC_DEFINE([IB_HAVE_PAUSE_INSTRUCTION], [1], [Does x86 PAUSE instruction exist])
+  fi
   ])
 
 # vim: set ft=config:

ut/ut0ut.c

@@ -391,6 +391,7 @@ ut_delay(
 
 	for (i = 0; i < delay * 50; i++) {
 		j += i;
+		UT_RELAX_CPU();
 	}
 
 	if (ut_always_false) {