-LEAF_ENTRY(hw_lock_to)
-1:
- movl L_ARG0,%edx /* fetch lock pointer */
- movl L_PC,%ecx
- /*
- * Attempt to grab the lock immediately
- * - fastpath without timeout nonsense.
- */
- DISABLE_PREEMPTION
- movl 0(%edx), %eax
- testl %eax,%eax /* lock locked? */
- jne 2f /* branch if so */
- lock; cmpxchgl %ecx,0(%edx) /* try to acquire the HW lock */
- jne 2f /* branch on failure */
- movl $1,%eax
- LEAF_RET
-
-2:
-#define INNER_LOOP_COUNT 1000
- /*
- * Failed to get the lock so set the timeout
- * and then spin re-checking the lock but pausing
- * every so many (INNER_LOOP_COUNT) spins to check for timeout.
- */
- movl L_ARG1,%ecx /* fetch timeout */
- push %edi
- push %ebx
- mov %edx,%edi
-
- rdtsc /* read cyclecount into %edx:%eax */
- addl %ecx,%eax /* fetch and timeout */
- adcl $0,%edx /* add carry */
- mov %edx,%ecx
- mov %eax,%ebx /* %ecx:%ebx is the timeout expiry */
-3:
- ENABLE_PREEMPTION /* no reason not to be preempted now */
-4:
- /*
- * The inner-loop spin to look for the lock being freed.
- */
- mov $(INNER_LOOP_COUNT),%edx
-5:
- PAUSE /* pause for hyper-threading */
- movl 0(%edi),%eax /* spin checking lock value in cache */
- testl %eax,%eax
- je 6f /* zero => unlocked, try to grab it */
- decl %edx /* decrement inner loop count */
- jnz 5b /* time to check for timeout? */
-
- /*
- * Here after spinning INNER_LOOP_COUNT times, check for timeout
- */
- rdtsc /* cyclecount into %edx:%eax */
- cmpl %ecx,%edx /* compare high-order 32-bits */
- jb 4b /* continue spinning if less, or */
- cmpl %ebx,%eax /* compare low-order 32-bits */
- jb 5b /* continue if less, else bail */
- xor %eax,%eax /* with 0 return value */
- pop %ebx
- pop %edi
- LEAF_RET
projects / apple / xnu.git / blobdiff