From 0a41e865845bfa5d7aafcc5fe000dafa26573fef Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 7 Jan 2012 15:38:52 -0500
Subject: [PATCH] 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
---
configure | 65 ++++++++++++++++++++++++++++++++++++
configure.in | 11 ++++++
src/include/pg_config.h.in | 3 ++
src/include/storage/s_lock.h | 25 ++++++++++++--
4 files changed, 102 insertions(+), 2 deletions(-)
diff --git a/configure b/configure
index 5cb3d9b14f0..af4f9a3d2cd 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 3f195a65117..9cad43620cc 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 e1b7fea49fc..db84f494ef7 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 9b02d1f5a40..074838e5251 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__ */
--
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