Changeset f1c7755 in mainline for kernel/arch/amd64/include/atomic.h

Timestamp:

2012-08-05T00:12:33Z (12 years ago)

Author:

Adam Hraska <adam.hraska+hos@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

b17518e

Parents:

6eaed07

Message:

Added atomic_swap_ptr() for ia32, amd64.

File:

• kernel/arch/amd64/include/atomic.h (modified) (1 diff)

kernel/arch/amd64/include/atomic.h

@@ -178 +178 @@
 }
 
+/** Atomicaly sets *ptr to new_val and returns the previous value. */
+NO_TRACE static inline void * atomic_swap_ptr(void **pptr, void *new_val)
+{
+        void *new_in_old_out = new_val;
+        
+        asm volatile (
+                "xchgq %[val], %[pptr]\n"
+                : [val] "+r" (new_in_old_out),
+                  [pptr] "+m" (*pptr)
+        );
+        
+        return new_in_old_out;
+}
+
+/** Sets *ptr to new_val and returns the previous value. NOT smp safe.
+ * 
+ * This function is only atomic wrt to local interrupts and it is
+ * NOT atomic wrt to other cpus.
+ */
+NO_TRACE static inline void * atomic_swap_ptr_local(void **pptr, void *new_val)
+{
+        /* 
+         * Issuing a xchg instruction always implies lock prefix semantics.
+         * Therefore, it is cheaper to use a cmpxchg without a lock prefix 
+         * in a loop.
+         */
+        void *exp_val;
+        void *old_val;
+        
+        do {
+                exp_val = *pptr;
+                old_val = atomic_cas_ptr_local(pptr, exp_val, new_val);
+        } while (old_val != exp_val);
+        
+        return old_val;
+}
+
+
 #undef _atomic_cas_ptr_impl