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 5a958a3441e7fbb8a898b1fa4dd62e9501c055cf..2b8f4272dc4e656d194b8672d1b3da827b4fc032 100755 (executable)
--- a/configure
+++ b/configure
@@ -18626,6 +18626,71 @@ _ACEOF
 fi
 
 
+echo "$as_me:$LINENO: checking for builtin locking functions" >&5
+echo $ECHO_N "checking for builtin locking functions... $ECHO_C" >&6
+if test "${pgac_cv_gcc_int_atomics+set}" = set; then
+  echo $ECHO_N "(cached) $ECHO_C" >&6
+else
+  cat >conftest.$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 { (eval echo "$as_me:$LINENO: \"$ac_link\"") >&5
+  (eval $ac_link) 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } &&
+        { ac_try='test -z "$ac_c_werror_flag"
+                        || test ! -s conftest.err'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; } &&
+        { ac_try='test -s conftest$ac_exeext'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }; then
+  pgac_cv_gcc_int_atomics="yes"
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+pgac_cv_gcc_int_atomics="no"
+fi
+rm -f conftest.err conftest.$ac_objext \
+      conftest$ac_exeext conftest.$ac_ext
+fi
+echo "$as_me:$LINENO: result: $pgac_cv_gcc_int_atomics" >&5
+echo "${ECHO_T}$pgac_cv_gcc_int_atomics" >&6
+if test x"$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 9414a8fc5ba64df7c89f1295c3f374f4c2815145..c067aabc4d3c179eaa12defcb2b347c7434435a6 100644 (file)
--- a/configure.in
+++ b/configure.in
@@ -1190,6 +1190,18 @@ AC_CHECK_FUNCS(atexit, [],
 
 AC_FUNC_FSEEKO
 
+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 e3a6c9982ad07cf67a533507e1cb23c1ecb43fca..f537360ee5da531c442d3452e79bfd5351fc826b 100644 (file)
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -148,6 +148,9 @@
 /* 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 7d9448fb7e48edc2532b542147d0938bb651e554..a3c15d4ffc83b50bca7eb0950b14afdc3609925b 100644 (file)
--- a/src/include/storage/s_lock.h
+++ b/src/include/storage/s_lock.h
@@ -252,13 +252,33 @@ 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)
 {
@@ -272,6 +292,7 @@ tas(volatile slock_t *lock)
        return (int) _res;
 }
 
+#endif  /* HAVE_GCC_INT_ATOMICS */
 #endif  /* __arm__ */