请教IoCompleteRequest和IoStartNextPacket调用的先后顺序问题

最近学习驱动开发，看《Programming the Windows Driver Modal》一书和DDK文档上面的DpcForIsr里面都是
先调用IoStartNextPacket启动下一个IRP的StartIo处理
再调用IoCompleteRequest完成当前IRP
 
而IoStartNextPacket内部就是调用IopStartNextPacket立即开始处理下一个IRP
那么岂不是后面的IRP反而比前面的IRP先完成？
 
请前辈指教。
 
以下内容为DDK文档中DpcForIsr的Comments
 
A DpcForIsr routine is typically responsible for at least thefollowing tasks:

• Completing the I/O operation described by the received IRP
• Dequeuing next IRP
  If the driver uses the system-supplied IRP queue, the DcpForIsrroutine should call IoStartNextPacket or IoStartNextPacketByKey, so the driver'sStartIo routine will start processing the next I/O request.
  If the driver uses internal IRP queues, the DpcForIsr routine shoulddequeue the next IRP and begin processing for the next I/O request.
• Setting the I/O status block in the received IRP and calling IoCompleteRequest for the completed request  

一个IRP, 每个驱动都经过一次

IoStartNextPacket 开始下一个IRP的一部分,IoCompleteRequest完成当前IRP,
IO管理器继续下一个IRP其他部分