Cisco Switching/Routing :: 3560 - Traffic Only Can Achieve Half Of Limit Bandwidth

I use WS-C3560G-24TS and try both ios 12.2.50.SE1 and 12.2.46.SE but problem the same. The config as following,
interface GigabitEthernet0/1
no switchport
ip address 1.1.1.2 255.255.255.0
[code].....
 
but I find the int g0/1 output traffic only can achieve about 500kbps then I try config below,

interface GigabitEthernet0/1
no switchport
[code]....
 
I find int g0/1 output traffic only can achieve about 5Mbps,but if I change "srr-queue bandwidth limit xx" command xx to 20-90,the int g0/1 can achieve normal traffic bps, for example,

interface GigabitEthernet0/1
no switchport
[code]...
 
the int g0/1 output can achieve 2Mbps that is correct,just only when limit set to 10%,the traffic only can achieve half of limit bandwidth.