Wasn't aware of it, so thanks for the question. I took a quick look and it looks like Agner is using performance counters, which, while being more accurate, are platform specific. One of the goals of lmbench was to be accurate across different platforms and CPU architectures. So it's all userland software only.
You can get pretty far that way, Carl wrote a userland tool called mhz that has been working without modification since around 1998 (when the fastest clock rate was 600mhz on an alpha). Still pretty accurate to this day when CPUs have clock rates 7x faster and fairly different architectures.
