Add detection of availability of the -mcx16 compiler flag to
the configure script. This flag is necessary on x86-64 to enable
cpmxchg16.
Implement 128-bit atomics if natively supported by the platform.
128-bit atomics are used by linux-generic timer implementation
on certain targets (e.g. x86-64) for lock-free implementation.
Signed-off-by: Ola Liljedahl <ola.liljed...@linaro.org>
---
configure.ac | 13 +++++
.../linux-generic/include/odp_atomic_internal.h | 62 ++++++++++++++++++++++
platform/linux-generic/odp_timer.c | 4 +-
3 files changed, 76 insertions(+), 3 deletions(-)
diff --git a/configure.ac b/configure.ac
index c59d2d1..7cd6670 100644
--- a/configure.ac
+++ b/configure.ac
@@ -207,6 +207,19 @@ ODP_CFLAGS="$ODP_CFLAGS -std=c99"
# Extra flags for example to suppress certain warning types
ODP_CFLAGS="$ODP_CFLAGS $ODP_CFLAGS_EXTRA"
+#########################################################################
+# Check if compiler supports cmpxchng16
+##########################################################################
+my_save_cflags="$CFLAGS"
+CFLAGS=-mcx16
+AC_MSG_CHECKING([whether CC supports -mcx16])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
+ [AC_MSG_RESULT([yes])]
+ [ODP_CFLAGS="$ODP_CFLAGS -mcx16"],
+ [AC_MSG_RESULT([no])]
+)
+CFLAGS="$my_save_cflags"
+
##########################################################################
# Default include setup
##########################################################################
diff --git a/platform/linux-generic/include/odp_atomic_internal.h
b/platform/linux-generic/include/odp_atomic_internal.h
index 093280f..3c5606c 100644
--- a/platform/linux-generic/include/odp_atomic_internal.h
+++ b/platform/linux-generic/include/odp_atomic_internal.h
@@ -587,6 +587,68 @@ static inline void
_odp_atomic_flag_clear(_odp_atomic_flag_t *flag)
__atomic_clear(flag, __ATOMIC_RELEASE);
}
+/* Check if target and compiler supports 128-bit scalars and corresponding
+ * exchange and CAS operations */
+/* GCC on x86-64 needs -mcx16 compiler option */
+#if defined __SIZEOF_INT128__ && defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16
+
+/** Preprocessor symbol that indicates support for 128-bit atomics */
+#define ODP_ATOMIC_U128
+
+/** An unsigned 128-bit (16-byte) scalar type */
+typedef __int128 _uint128_t;
+
+/** Atomic 128-bit type */
+typedef struct {
+ _uint128_t v; /**< Actual storage for the atomic variable */
+} _odp_atomic_u128_t ODP_ALIGNED(16);
+
+/**
+ * 16-byte atomic exchange operation
+ *
+ * @param ptr Pointer to a 16-byte atomic variable
+ * @param val Pointer to new value to write
+ * @param old Pointer to location for old value
+ * @param mmodel Memory model associated with the exchange operation
+ */
+static inline void _odp_atomic_u128_xchg_mm(_odp_atomic_u128_t *ptr,
+ _uint128_t *val,
+ _uint128_t *old,
+ _odp_memmodel_t mm)
+{
+ __atomic_exchange(&ptr->v, val, old, mm);
+}
+
+/**
+ * Atomic compare and exchange (swap) of 16-byte atomic variable
+ * "Strong" semantics, will not fail spuriously.
+ *
+ * @param ptr Pointer to a 16-byte atomic variable
+ * @param exp Pointer to expected value (updated on failure)
+ * @param val Pointer to new value to write
+ * @param succ Memory model associated with a successful compare-and-swap
+ * operation
+ * @param fail Memory model associated with a failed compare-and-swap
+ * operation
+ *
+ * @retval 1 exchange successul
+ * @retval 0 exchange failed and '*exp' updated with current value
+ */
+static inline int _odp_atomic_u128_cmp_xchg_mm(_odp_atomic_u128_t *ptr,
+ _uint128_t *exp,
+ _uint128_t *val,
+ _odp_memmodel_t succ,
+ _odp_memmodel_t fail)
+{
+ return __atomic_compare_exchange(&ptr->v, exp, val,
+ false/*strong*/, succ, fail);
+}
+#endif
+
+/**
+ * @}
+ */
+
#ifdef __cplusplus
}
#endif
diff --git a/platform/linux-generic/odp_timer.c
b/platform/linux-generic/odp_timer.c
index 6b84309..41e7195 100644
--- a/platform/linux-generic/odp_timer.c
+++ b/platform/linux-generic/odp_timer.c
@@ -11,9 +11,7 @@
*
*/
-/* Check if compiler supports 16-byte atomics. GCC needs -mcx16 flag on x86 */
-/* Using spin lock actually seems faster on Core2 */
-#ifdef ODP_ATOMIC_U128
+#if __SIZEOF_POINTER__ != 8
/* TB_NEEDS_PAD defined if sizeof(odp_buffer_t) != 8 */
#define TB_NEEDS_PAD
#define TB_SET_PAD(x) ((x).pad = 0)
--
2.5.0
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