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>

@@ -97,16 +97,26 @@
         avl_tree_t      vc_offset_tree;
         avl_tree_t      vc_lastused_tree;
         kmutex_t        vc_lock;
 };
 
+typedef struct vdev_queue_class {
+        uint32_t        vqc_active;
+
+        /*
+         * Sorted by offset or timestamp, depending on if the queue is
+         * LBA-ordered vs FIFO.
+         */
+        avl_tree_t      vqc_queued_tree;
+} vdev_queue_class_t;
+
 struct vdev_queue {
-        avl_tree_t      vq_deadline_tree;
-        avl_tree_t      vq_read_tree;
-        avl_tree_t      vq_write_tree;
-        avl_tree_t      vq_pending_tree;
-        hrtime_t        vq_io_complete_ts;
+        vdev_t          *vq_vdev;
+        vdev_queue_class_t vq_class[ZIO_PRIORITY_NUM_QUEUEABLE];
+        avl_tree_t      vq_active_tree;
+        uint64_t        vq_last_offset;
+        hrtime_t        vq_io_complete_ts; /* time last i/o completed */
         kmutex_t        vq_lock;
 };
 
 /*
  * Virtual device descriptor