4045 zfs write throttle & i/o scheduler performance work
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>

@@ -3255,21 +3255,21 @@
 
         if (vd->vdev_ops->vdev_op_leaf) {
                 vdev_queue_t *vq = &vd->vdev_queue;
 
                 mutex_enter(&vq->vq_lock);
-                if (avl_numnodes(&vq->vq_pending_tree) > 0) {
+                if (avl_numnodes(&vq->vq_active_tree) > 0) {
                         spa_t *spa = vd->vdev_spa;
                         zio_t *fio;
                         uint64_t delta;
 
                         /*
                          * Look at the head of all the pending queues,
                          * if any I/O has been outstanding for longer than
                          * the spa_deadman_synctime we panic the system.
                          */
-                        fio = avl_first(&vq->vq_pending_tree);
+                        fio = avl_first(&vq->vq_active_tree);
                         delta = gethrtime() - fio->io_timestamp;
                         if (delta > spa_deadman_synctime(spa)) {
                                 zfs_dbgmsg("SLOW IO: zio timestamp %lluns, "
                                     "delta %lluns, last io %lluns",
                                     fio->io_timestamp, delta,