From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 7 Jan 2012 20:38:52 +0000 (-0500)
Subject: Use __sync_lock_test_and_set() for spinlocks on ARM, if available.
X-Git-Tag: REL9_2_BETA1~607
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=0a41e865845bfa5d7aafcc5fe000dafa26573fef;p=postgresql

Use __sync_lock_test_and_set() for spinlocks on ARM, if available.

Historically we've used the SWPB instruction for TAS() on ARM, but this
is deprecated and not available on ARMv6 and later.  Instead, make use
of a GCC builtin if available.  We'll still fall back to SWPB if not,
so as not to break existing ports using older GCC versions.

Eventually we might want to try using __sync_lock_test_and_set() on some
other architectures too, but for now that seems to present only risk and
not reward.

Back-patch to all supported versions, since people might want to use any
of them on more recent ARM chips.

Martin Pitt
---

diff --git a/configure b/configure
index 5cb3d9b14f..af4f9a3d2c 100755
--- a/configure
+++ b/configure
@@ -22596,6 +22596,71 @@ fi
 done
 
 
+{ $as_echo "$as_me:$LINENO: checking for builtin locking functions" >&5
+$as_echo_n "checking for builtin locking functions... " >&6; }
+if test "${pgac_cv_gcc_int_atomics+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+int
+main ()
+{
+int lock = 0;
+   __sync_lock_test_and_set(&lock, 1);
+   __sync_lock_release(&lock);
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext conftest$ac_exeext
+if { (ac_try="$ac_link"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_link") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest$ac_exeext && {
+	 test "$cross_compiling" = yes ||
+	 $as_test_x conftest$ac_exeext
+       }; then
+  pgac_cv_gcc_int_atomics="yes"
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	pgac_cv_gcc_int_atomics="no"
+fi
+
+rm -rf conftest.dSYM
+rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
+      conftest$ac_exeext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:$LINENO: result: $pgac_cv_gcc_int_atomics" >&5
+$as_echo "$pgac_cv_gcc_int_atomics" >&6; }
+if test x"$pgac_cv_gcc_int_atomics" = x"yes"; then
+
+cat >>confdefs.h <<\_ACEOF
+#define HAVE_GCC_INT_ATOMICS 1
+_ACEOF
+
+fi
+
 
 #
 # Pthreads
diff --git a/configure.in b/configure.in
index 3f195a6511..9cad43620c 100644
--- a/configure.in
+++ b/configure.in
@@ -1454,6 +1454,17 @@ fi
 AC_CHECK_FUNCS([strtoll strtoq], [break])
 AC_CHECK_FUNCS([strtoull strtouq], [break])
 
+AC_CACHE_CHECK([for builtin locking functions], pgac_cv_gcc_int_atomics,
+[AC_TRY_LINK([],
+  [int lock = 0;
+   __sync_lock_test_and_set(&lock, 1);
+   __sync_lock_release(&lock);],
+  [pgac_cv_gcc_int_atomics="yes"],
+  [pgac_cv_gcc_int_atomics="no"])])
+if test x"$pgac_cv_gcc_int_atomics" = x"yes"; then
+  AC_DEFINE(HAVE_GCC_INT_ATOMICS, 1, [Define to 1 if you have __sync_lock_test_and_set(int *) and friends.])
+fi
+
 
 #
 # Pthreads
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index e1b7fea49f..db84f494ef 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -179,6 +179,9 @@
 /* Define to 1 if your compiler understands __FUNCTION__. */
 #undef HAVE_FUNCNAME__FUNCTION
 
+/* Define to 1 if you have __sync_lock_test_and_set(int *) and friends. */
+#undef HAVE_GCC_INT_ATOMICS
+
 /* Define to 1 if you have the `getaddrinfo' function. */
 #undef HAVE_GETADDRINFO
 
diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h
index 9b02d1f5a4..074838e525 100644
--- a/src/include/storage/s_lock.h
+++ b/src/include/storage/s_lock.h
@@ -275,13 +275,33 @@ tas(volatile slock_t *lock)
 #endif	 /* __ia64__ || __ia64 */
 
 
+/*
+ * On ARM, we use __sync_lock_test_and_set(int *, int) if available, and if
+ * not fall back on the SWPB instruction.  SWPB does not work on ARMv6 or
+ * later, so the compiler builtin is preferred if available.  Note also that
+ * the int-width variant of the builtin works on more chips than other widths.
+ */
 #if defined(__arm__) || defined(__arm)
 #define HAS_TEST_AND_SET
 
-typedef unsigned char slock_t;
-
 #define TAS(lock) tas(lock)
 
+#ifdef HAVE_GCC_INT_ATOMICS
+
+typedef int slock_t;
+
+static __inline__ int
+tas(volatile slock_t *lock)
+{
+	return __sync_lock_test_and_set(lock, 1);
+}
+
+#define S_UNLOCK(lock) __sync_lock_release(lock)
+
+#else /* !HAVE_GCC_INT_ATOMICS */
+
+typedef unsigned char slock_t;
+
 static __inline__ int
 tas(volatile slock_t *lock)
 {
@@ -295,6 +315,7 @@ tas(volatile slock_t *lock)
 	return (int) _res;
 }
 
+#endif	 /* HAVE_GCC_INT_ATOMICS */
 #endif	 /* __arm__ */