Messages in this thread Patch in this message | | | From | Michel Lespinasse <> | Subject | [PATCH 09/11] rwsem: down_read_critical infrastructure support | Date | Mon, 24 May 2010 13:31:19 -0700 |
| |
Add rwsem_down_read_unfair_failed() function in the non-generic rwsem library code, similar to rwsem_down_read_failed() except that blocked threads are placed at the head of the queue.
Make the waiter type an enumeration rather than a bitmask.
Signed-off-by: Michel Lespinasse <walken@google.com> Signed-off-by: David Howells <dhowells@redhat.com> --- lib/rwsem.c | 40 +++++++++++++++++++++++++++++++--------- 1 files changed, 31 insertions(+), 9 deletions(-)
diff --git a/lib/rwsem.c b/lib/rwsem.c index f236d7c..72454f4 100644 --- a/lib/rwsem.c +++ b/lib/rwsem.c @@ -28,12 +28,16 @@ void __init_rwsem(struct rw_semaphore *sem, const char *name, EXPORT_SYMBOL(__init_rwsem); +enum rwsem_waiter_type { + RWSEM_WAITING_FOR_WRITE, + RWSEM_WAITING_FOR_READ, + RWSEM_WAITING_FOR_UNFAIR_READ +}; + struct rwsem_waiter { struct list_head list; struct task_struct *task; - unsigned int flags; -#define RWSEM_WAITING_FOR_READ 0x00000001 -#define RWSEM_WAITING_FOR_WRITE 0x00000002 + enum rwsem_waiter_type type; }; /* Wake types for __rwsem_do_wake(). Note that RWSEM_WAKE_NO_ACTIVE and @@ -63,7 +67,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type) signed long oldcount, woken, loop, adjustment; waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); - if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE)) + if (waiter->type != RWSEM_WAITING_FOR_WRITE) goto readers_only; if (wake_type == RWSEM_WAKE_READ_OWNED) @@ -132,10 +136,10 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type) waiter = list_entry(waiter->list.next, struct rwsem_waiter, list); - } while (waiter->flags & RWSEM_WAITING_FOR_READ); + } while (waiter->type != RWSEM_WAITING_FOR_WRITE); adjustment = woken * RWSEM_ACTIVE_READ_BIAS; - if (waiter->flags & RWSEM_WAITING_FOR_READ) + if (waiter->type != RWSEM_WAITING_FOR_WRITE) /* hit end of list above */ adjustment -= RWSEM_WAITING_BIAS; @@ -171,7 +175,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type) */ static struct rw_semaphore __sched * rwsem_down_failed_common(struct rw_semaphore *sem, - unsigned int flags, signed long adjustment) + enum rwsem_waiter_type type, signed long adjustment) { struct rwsem_waiter waiter; struct task_struct *tsk = current; @@ -182,12 +186,16 @@ rwsem_down_failed_common(struct rw_semaphore *sem, /* set up my own style of waitqueue */ spin_lock_irq(&sem->wait_lock); waiter.task = tsk; - waiter.flags = flags; + waiter.type = type; get_task_struct(tsk); if (list_empty(&sem->wait_list)) adjustment += RWSEM_WAITING_BIAS; - list_add_tail(&waiter.list, &sem->wait_list); + + if (type == RWSEM_WAITING_FOR_UNFAIR_READ) + list_add(&waiter.list, &sem->wait_list); + else + list_add_tail(&waiter.list, &sem->wait_list); /* we're now waiting on the lock, but no longer actively locking */ count = rwsem_atomic_update(adjustment, sem); @@ -229,6 +237,20 @@ rwsem_down_read_failed(struct rw_semaphore *sem) -RWSEM_ACTIVE_READ_BIAS); } +#ifdef __HAVE_DOWN_READ_UNFAIR + +/* + * wait for the read lock to be granted - skip waiting threads + */ +asmregparm struct rw_semaphore __sched * +rwsem_down_read_unfair_failed(struct rw_semaphore *sem) +{ + return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_UNFAIR_READ, + -RWSEM_ACTIVE_READ_BIAS); +} + +#endif + /* * wait for the write lock to be granted */ -- 1.7.0.1
| |