在计算ce interface上的利用率的时候，我用了下面的公式：

bandwidth/linkspeed.

bandwidth中包含了input 和output. 对于一个100M的网卡，如果运行在全双工模式下，linkspeed这个分母应该是100M还是200M？如果是半双工模式下，应该是50M还是100M？

You are mixing up the concepts. Let me put it this way:

Half duplex is a one-lane street. A car can travel either from left to right or from right to left but no both at the same time. The speed limit of this street is 100km/h.
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----> or <------
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Full duplex is a two-lane street. Cars can travel from left to right and right to left at the same time. The speed limit is also 100km/h
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------->
----------------------
         <------------
_______________

If the one-lane street is not busy, you can drive your car from left to right at 100km/h and immediately drive it back at 100km/h. It is as fast as you travel on a two-lane street. However, if the one-lane street is busy, after you drive from left to right, you have to wait until there is no traffic. Then you can drive back at 100km/h. While on a two-lane street, you don't have to wait to drive back. In either scenarios, the maximum speed is always 100km/h. Full duplex is quicker not becuase of its speed but because of its width.

Hope this helps