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>

*** 97,112 ****
          avl_tree_t      vc_offset_tree;
          avl_tree_t      vc_lastused_tree;
          kmutex_t        vc_lock;
  };
  
  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;
          kmutex_t        vq_lock;
  };
  
  /*
   * Virtual device descriptor
--- 97,122 ----
          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 {
!         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