smile 
Hi, everybody
Ethernet performance is so low(just 6mbps by iperf). so I inspect of it.
Usb ethernet connection have some wrong because it's connect by full speed.
I don't know why i connected by full speed not high-speed.
Only dm9620 is connected by full speed as follows.
[root@DC /dc]$ lsusb -t
lsusb: cannot open "/usr/share/hwdata/usb.ids", No such file or directory
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=exynos-ohci/3p, 12M
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=s5p-ehci/3p, 480M
|__ Port 2: Dev 2, If 0, Class=, Driver=hub/5p, 480M
|__ Port 1: Dev 3, If 0, Class=, Driver=dm9620, 12M
|__ Port 5: Dev 5, If 0, Class=, Driver=, 480M
Tell me how to fix it,plz