push disk io for client-linux.py

clients/client-psutil.py

@@ -201,6 +201,10 @@ def _disk_io():
         after the interval.
         Return a tuple including all currently running processes
         sorted by IO activity and total disks I/O activity.
+    磁盘IO：因为IOPS原因，SSD和HDD、包括RAID卡，ZFS等。IO对性能的影响还需要结合自身服务器情况来判断。
+    比如我这里是机械硬盘，大量做随机小文件读写，那么很低的读写也就能造成硬盘长时间的等待。
+    如果这里做连续性IO，那么普通机械硬盘写入到100Mb/s，那么也能造成硬盘长时间的等待。
+    磁盘读写有误差：4k，8k ，https://stackoverflow.com/questions/34413926/psutil-vs-dd-monitoring-disk-i-o
     """
     while True:
         # first get a list of all processes and disk io counters