A system, apparatus and method for gathering monitoring data relating to the operation of a data processing system are disclosed. The data processing system comprises a monitor controller and a plurality of monitors which gather monitoring data relating to the operation of the data processing system. Each monitor does not send its monitoring data to the monitor controller unsolicited, but merely indicates to the monitor controller that it has such data ready for transmission. In response to reception of a data ready signal from more than one monitor, the monitor controller selects one of these monitors and sends it a data transmission command, thereby avoiding resource contention in a shared resource between data transmissions from more than one monitor.