Commit cbea5ac1 authored by Chris Mason's avatar Chris Mason
Browse files

Btrfs: reduce calls to wake_up on uncontended locks 



The btrfs locks were unconditionally calling wake_up as the
locks were released.  This lead to extra thrashing on the waitqueue,
especially for locks that were dominated by readers.

Signed-off-by: default avatarChris Mason <chris.mason@fusionio.com>
parent e39e64ac

fs/btrfs/locking.c

+9 −5
Original line number Diff line number Diff line
@@ -78,13 +78,15 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw) 
		write_lock(&eb->lock);

		WARN_ON(atomic_read(&eb->spinning_writers));

		atomic_inc(&eb->spinning_writers);

		if (atomic_dec_and_test(&eb->blocking_writers))

		if (atomic_dec_and_test(&eb->blocking_writers) &&

		    waitqueue_active(&eb->write_lock_wq))

			wake_up(&eb->write_lock_wq);

	} else if (rw == BTRFS_READ_LOCK_BLOCKING) {

		BUG_ON(atomic_read(&eb->blocking_readers) == 0);

		read_lock(&eb->lock);

		atomic_inc(&eb->spinning_readers);

		if (atomic_dec_and_test(&eb->blocking_readers))

		if (atomic_dec_and_test(&eb->blocking_readers) &&

		    waitqueue_active(&eb->read_lock_wq))

			wake_up(&eb->read_lock_wq);

	}

	return;
@@ -199,7 +201,8 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb) 
	}

	btrfs_assert_tree_read_locked(eb);

	WARN_ON(atomic_read(&eb->blocking_readers) == 0);

	if (atomic_dec_and_test(&eb->blocking_readers))

	if (atomic_dec_and_test(&eb->blocking_readers) &&

	    waitqueue_active(&eb->read_lock_wq))

		wake_up(&eb->read_lock_wq);

	atomic_dec(&eb->read_locks);

}
@@ -247,7 +250,8 @@ void btrfs_tree_unlock(struct extent_buffer *eb) 
	if (blockers) {

		WARN_ON(atomic_read(&eb->spinning_writers));

		atomic_dec(&eb->blocking_writers);

		smp_wmb();

		smp_mb();

		if (waitqueue_active(&eb->write_lock_wq))

			wake_up(&eb->write_lock_wq);

	} else {

		WARN_ON(atomic_read(&eb->spinning_writers) != 1);