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Yep, your right, I checked the cisco documentation as below:-

Usage Guidelines
If you configure this command to 80 percent, the port is idle 20 percent of the time. The line rate drops to 80 percent of the connected speed. These values are not exact because the hardware adjusts the line rate in increments of six.

This example shows how to limit a port to 800 Mb/s:

Switch(config)# interface gigabitethernet0/1

Switch(config-if)# srr-queue bandwidth limit 80