kern/mutex: new adaptive spinning mutex implementation

1 files changed, 120 insertions, 0 deletions

diff --git a/kern/mutex/mutex_adaptive_i.h b/kern/mutex/mutex_adaptive_i.h
new file mode 100644
index 00000000..2dd06792
--- /dev/null
+++ b/kern/mutex/mutex_adaptive_i.h
@@ -0,0 +1,120 @@
+/*
+ * Copyright (c) 2017 Agustina Arzille.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _KERN_MUTEX_ADAPTIVE_I_H
+#define _KERN_MUTEX_ADAPTIVE_I_H
+
+#ifndef _KERN_MUTEX_H
+#error "don't include <kern/mutex/mutex_adaptive_i.h> directly," \
+       " use <kern/mutex.h> instead"
+#endif
+
+#include <stdint.h>
+
+#include <kern/assert.h>
+#include <kern/atomic.h>
+#include <kern/error.h>
+#include <kern/macros.h>
+#include <kern/mutex_types.h>
+#include <kern/thread.h>
+
+/*
+ * Mutex flags.
+ *
+ * The "contended" flag indicates that threads are waiting for the mutex
+ * to be unlocked, potentially spinning on the owner. It forces threads
+ * trying to lock the mutex as well as the owner to take the slow path.
+ */
+#define MUTEX_ADAPTIVE_CONTENDED 0x1
+
+static inline void
+mutex_adaptive_init(struct mutex *mutex)
+{
+    mutex->owner = 0;
+}
+
+#define mutex_adaptive_assert_locked(mutex) assert((mutex)->owner != 0)
+
+static inline int
+mutex_adaptive_lock_fast(struct mutex *mutex)
+{
+    uintptr_t owner;
+
+    owner = atomic_cas_acquire(&mutex->owner, 0, (uintptr_t)thread_self());
+
+    if (unlikely(owner != 0)) {
+        return ERROR_BUSY;
+    }
+
+    return 0;
+}
+
+static inline int
+mutex_adaptive_unlock_fast(struct mutex *mutex)
+{
+    uintptr_t owner;
+
+    owner = atomic_cas_release(&mutex->owner, (uintptr_t)thread_self(), 0);
+
+    if (unlikely(owner & MUTEX_ADAPTIVE_CONTENDED)) {
+        return ERROR_BUSY;
+    }
+
+    return 0;
+}
+
+void mutex_adaptive_lock_slow(struct mutex *mutex);
+void mutex_adaptive_unlock_slow(struct mutex *mutex);
+
+/*
+ * Interface exported to the public mutex header.
+ */
+
+#define mutex_impl_init             mutex_adaptive_init
+#define mutex_impl_assert_locked    mutex_adaptive_assert_locked
+
+static inline int
+mutex_impl_trylock(struct mutex *mutex)
+{
+    return mutex_adaptive_lock_fast(mutex);
+}
+
+static inline void
+mutex_impl_lock(struct mutex *mutex)
+{
+    int error;
+
+    error = mutex_adaptive_lock_fast(mutex);
+
+    if (unlikely(error)) {
+        mutex_adaptive_lock_slow(mutex);
+    }
+}
+
+static inline void
+mutex_impl_unlock(struct mutex *mutex)
+{
+    int error;
+
+    error = mutex_adaptive_unlock_fast(mutex);
+
+    if (unlikely(error)) {
+        mutex_adaptive_unlock_slow(mutex);
+    }
+}
+
+#endif /* _KERN_MUTEX_ADAPTIVE_I_H */