On Fri, 2015-04-24 at 13:54 -0400, Waiman Long wrote: > This patch also checks one more time in __rwsem_do_wake() to see if > the rwsem was stolen just before doing the expensive wakeup operation > which will be unnecessary if the lock was stolen.
It strikes me that this should be another patch, as the optimization is independent of the wake_lock (comments below). [...] > +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER Could you please reuse the CONFIG_RWSEM_SPIN_ON_OWNER ifdefiry we already have? Just add these where we define rwsem_spin_on_owner(). [...] > /* > * handle the lock release when processes blocked on it that can now run > * - if we come here from up_xxxx(), then: > @@ -125,6 +154,14 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum > rwsem_wake_type wake_type) > struct list_head *next; > long oldcount, woken, loop, adjustment; > > + /* > + * up_write() cleared the owner field before calling this function. > + * If that field is now set, a writer must have stolen the lock and > + * the wakeup operation should be aborted. > + */ > + if (rwsem_has_active_writer(sem)) > + goto out; We currently allow small races between rwsem owner and counter checks. And __rwsem_do_wake() can be called by checking the former -- and lock stealing is done with the counter as well. Please see below how we back out of such cases, as it is very much considered when granting the next reader. So nack to this as is, sorry. Thanks, Davidlohr -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
