an implementation of the Mellor-Crummey Scott (MCS) lock

arch/x86/kernel/include/arch-lock.h

@@ -5,6 +5,7 @@
 #define __HEADER_X86_COMMON_ARCH_LOCK
 
 #include <ihk/cpu.h>
+#include <ihk/atomic.h>
 
 //#define DEBUG_SPINLOCK
 
@@ -99,5 +100,59 @@ static void ihk_mc_spinlock_unlock(ihk_spinlock_t *lock, unsigned long flags)
 #endif
 }
 
+
+/* An implementation of the Mellor-Crummey Scott (MCS) lock */
+typedef struct mcs_lock_node {
+	unsigned long locked;
+	struct mcs_lock_node *next;
+} __attribute__((aligned(64))) mcs_lock_node_t;
+
+static void mcs_lock_init(struct mcs_lock_node *node)
+{
+	node->locked = 0;
+	node->next = NULL;
+}
+
+static void mcs_lock_lock(struct mcs_lock_node *lock,
+		struct mcs_lock_node *node)
+{
+	struct mcs_lock_node *pred;
+
+	node->next = NULL;
+	node->locked = 0;
+	pred = (struct mcs_lock_node *)xchg8((unsigned long *)&lock->next,
+			(unsigned long)node);
+
+	if (pred) {
+		node->locked = 1;
+		pred->next = node;
+		while (node->locked != 0) {
+			cpu_pause();
+		}
+	}
+}
+
+static void mcs_lock_unlock(struct mcs_lock_node *lock,
+		struct mcs_lock_node *node)
+{
+	if (node->next == NULL) {
+		struct mcs_lock_node *old = (struct mcs_lock_node *)
+			atomic_cmpxchg8((unsigned long *)&lock->next,
+					(unsigned long)node, (unsigned long)0);
+
+		if (old == node) {
+			return;
+		}
+
+		while (node->next == NULL) {
+			cpu_pause();
+		}
+	}
+
+	node->next->locked = 0;
+}
+
+
+
 #endif
 

arch/x86/kernel/include/ihk/atomic.h

@@ -112,6 +112,17 @@ static inline int ihk_atomic_sub_return(int i, ihk_atomic_t *v)
 	__x;								\
 })
 
+static inline unsigned long xchg8(unsigned long *ptr, unsigned long x)
+{
+	unsigned long __x = (x);
+	asm volatile("xchgq %0,%1"
+			 : "=r" (__x)
+			 : "m" (*(volatile unsigned long*)(ptr)), "0" (__x)
+			 : "memory");
+
+	return __x;
+}
+
 #define __xchg(x, ptr, size)						\
 ({									\
 	__typeof(*(ptr)) __x = (x);					\
@@ -150,5 +161,17 @@ static inline int ihk_atomic_sub_return(int i, ihk_atomic_t *v)
 #define xchg(ptr, v)							\
 	__xchg((v), (ptr), sizeof(*ptr))
 
+static inline unsigned long atomic_cmpxchg8(unsigned long *addr,
+		unsigned long oldval,
+		unsigned long newval)
+{
+	asm volatile("lock; cmpxchgq %3, %1\n"
+		     : "=a" (oldval), "+m" (*addr)
+		     : "r" (newval), "0" (oldval)
+		     : "memory"
+	);
+
+	return oldval;
+}
 
 #endif