For example, On OCTEON single-chip systems we synchronize the the counters and they don't drift. So, we can use CPO.Count. However, on two-chip NUMA configurations there may be clock drift between the two chips, so CPO.Count cannot be used as a clocksource. We have a single kernel image that runs on both types of systems, so we have to be able to enable/disable the gettimeofday() acceleration.Much more interesting the situation then there are a different clock frequency in different CPUs.