Control of instruction pipeline in data processing system

In a data processing system having an instruction pipeline in which each instruction is allotted for execution, part by part, to segments provided in the instruction pipeline so that the first segment executes a part of one instruction allotted thereto, while the successive segments execute respective parts of the preceding instructions allotted thereto, a control of the instruction pipeline is arranged to provide the segments with individual reference clock signals whose timings are determined separately depending on the capacity of each segment for execution of the allotted part of each instruction and also variable depending on the actual condition of the system in execution of each instruction.