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rwsem: simplify __rwsem_do_wake

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This is mostly for cleanup value:

- We don't need several gotos to handle the case where the first
  waiter is a writer. Two simple tests will do (and generate very
  similar code).

- In the remainder of the function, we know the first waiter is a reader,
  so we don't have to double check that. We can use do..while loops
  to iterate over the readers to wake (generates slightly better code).

Signed-off-by: Michel Lespinasse <[email protected]>
Reviewed-by: Peter Hurley <[email protected]>
Acked-by: Davidlohr Bueso <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Michel Lespinasse 2013-05-07 06:45:58 -07:00 • committed by Linus Torvalds
commit 8cf5322ce6
2 changed files with 19 additions and 30 deletions
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26
lib/rwsem.c
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@ -68,20 +68,17 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type)
signed long woken, loop, adjustment;
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
if (waiter->type != RWSEM_WAITING_FOR_WRITE)
goto readers_only;
if (wake_type == RWSEM_WAKE_READ_OWNED)
/* Another active reader was observed, so wakeup is not
* likely to succeed. Save the atomic op.
*/
if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
if (wake_type != RWSEM_WAKE_READ_OWNED)
/* Wake writer at the front of the queue, but do not
* grant it the lock yet as we want other writers
* to be able to steal it. Readers, on the other hand,
* will block as they will notice the queued writer.
*/
wake_up_process(waiter->task);
goto out;
}
/* Wake up the writing waiter and let the task grab the sem: */
wake_up_process(waiter->task);
goto out;
readers_only:
/* If we come here from up_xxxx(), another thread might have reached
* rwsem_down_failed_common() before we acquired the spinlock and
* woken up a waiter, making it now active. We prefer to check for
@ -125,7 +122,8 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type)
rwsem_atomic_add(adjustment, sem);
next = sem->wait_list.next;
for (loop = woken; loop > 0; loop--) {
loop = woken;
do {
waiter = list_entry(next, struct rwsem_waiter, list);
next = waiter->list.next;
tsk = waiter->task;
@ -133,7 +131,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type)
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
}
} while (--loop);
sem->wait_list.next = next;
next->prev = &sem->wait_list;