3 files changed, 157 insertions, 0 deletions
diff --git a/src/util/Makefile.sources b/src/util/Makefile.sources
index c7f6516a992..9393f6a4816 100644
--- a/src/util/Makefile.sources
+++ b/src/util/Makefile.sources
@@ -35,6 +35,7 @@ MESA_UTIL_FILES := \
 	set.c \
 	set.h \
 	simple_list.h \
+	simple_mtx.h \
 	slab.c \
 	slab.h \
 	string_buffer.c \
diff --git a/src/util/meson.build b/src/util/meson.build
index c9cb3e861e9..0145d9cbe33 100644
--- a/src/util/meson.build
+++ b/src/util/meson.build
@@ -59,6 +59,7 @@ files_mesa_util = files(
   'set.c',
   'set.h',
   'simple_list.h',
+  'simple_mtx.h',
   'slab.c',
   'slab.h',
   'string_buffer.c',
diff --git a/src/util/simple_mtx.h b/src/util/simple_mtx.h
new file mode 100644
index 00000000000..86ba026e61c
--- /dev/null
+++ b/src/util/simple_mtx.h
@@ -0,0 +1,155 @@
+/*
+ * Copyright © 2015 Intel
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#ifndef _SIMPLE_MTX_H
+#define _SIMPLE_MTX_H
+
+#include "c11/threads.h"
+
+#if defined(__GNUC__) && defined(HAVE_LINUX_FUTEX_H)
+
+/* mtx_t - Fast, simple mutex
+ *
+ * While modern pthread mutexes are very fast (implemented using futex), they
+ * still incur a call to an external DSO and overhead of the generality and
+ * features of pthread mutexes.  Most mutexes in mesa only needs lock/unlock,
+ * and the idea here is that we can inline the atomic operation and make the
+ * fast case just two intructions.  Mutexes are subtle and finicky to
+ * implement, so we carefully copy the implementation from Ulrich Dreppers
+ * well-written and well-reviewed paper:
+ *
+ *   "Futexes Are Tricky"
+ *   http://www.akkadia.org/drepper/futex.pdf
+ *
+ * We implement "mutex3", which gives us a mutex that has no syscalls on
+ * uncontended lock or unlock.  Further, the uncontended case boils down to a
+ * locked cmpxchg and an untaken branch, the uncontended unlock is just a
+ * locked decr and an untaken branch.  We use __builtin_expect() to indicate
+ * that contention is unlikely so that gcc will put the contention code out of
+ * the main code flow.
+ *
+ * A fast mutex only supports lock/unlock, can't be recursive or used with
+ * condition variables.
+ */
+
+typedef struct {
+   uint32_t val;
+} simple_mtx_t;
+
+#define _SIMPLE_MTX_INITIALIZER_NP { 0 }
+
+#include <stdint.h>
+#include <linux/futex.h>
+#include <sys/time.h>
+#include <sys/syscall.h>
+
+static inline long sys_futex(void *addr1, int op, int val1,
+                             struct timespec *timeout, void *addr2, int val3)
+{
+   return syscall(SYS_futex, addr1, op, val1, timeout, addr2, val3);
+}
+
+static inline int futex_wake(uint32_t *addr, int count)
+{
+   return sys_futex(addr, FUTEX_WAKE, count, NULL, NULL, 0);
+}
+
+static inline int futex_wait(uint32_t *addr, int32_t value)
+{
+   return sys_futex(addr, FUTEX_WAIT, value, NULL, NULL, 0);
+}
+
+static inline void
+simple_mtx_init(simple_mtx_t *mtx, int type)
+{
+   assert(type == mtx_plain);
+
+   mtx->val = 0;
+}
+
+static inline void
+simple_mtx_destroy(simple_mtx_t *mtx)
+{
+}
+
+static inline void
+simple_mtx_lock(simple_mtx_t *mtx)
+{
+   uint32_t c;
+
+   c = __sync_val_compare_and_swap(&mtx->val, 0, 1);
+   if (__builtin_expect(c != 0, 0)) {
+      if (c != 2)
+         c = __sync_lock_test_and_set(&mtx->val, 2);
+      while (c != 0) {
+         futex_wait(&mtx->val, 2);
+         c = __sync_lock_test_and_set(&mtx->val, 2);
+      }
+   }
+}
+
+static inline void
+simple_mtx_unlock(simple_mtx_t *mtx)
+{
+   uint32_t c;
+
+   c = __sync_fetch_and_sub(&mtx->val, 1);
+   if (__builtin_expect(c != 1, 0)) {
+      mtx->val = 0;
+      futex_wake(&mtx->val, 1);
+   }
+}
+
+#else
+
+typedef mtx_t simple_mtx_t;
+
+#define _SIMPLE_MTX_INITIALIZER_NP _MTX_INITIALIZER_NP
+
+static inline void
+simple_mtx_init(simple_mtx_t *mtx, int type)
+{
+   mtx_init(mtx, type);
+}
+
+static inline void
+simple_mtx_destroy(simple_mtx_t *mtx)
+{
+   mtx_destroy(mtx);
+}
+
+static inline void
+simple_mtx_lock(simple_mtx_t *mtx)
+{
+   mtx_lock(mtx);
+}
+
+static inline void
+simple_mtx_unlock(simple_mtx_t *mtx)
+{
+   mtx_unlock(mtx);
+}
+
+#endif
+
+#endif