clk: timestamps

Hi All, In the kernel code I see it supports CLOCK_REALTIME \ CLOCK_MONOTONIC \ CLOCK_MONOTONIC_RAW timestamps. Can someone explain what’s major difference between those three modes and when to use which one? I’ve N number of Linux machines in the network with the same software running. Basically I need to collect the timestamps in kernel mode in all the machines and then compare, which(either CLOCK_REALTIME or CLOCK_MONOTIC_RAW or MONOTONIC) one would be the correct way? Thanks,