A data processing apparatus and method are provided for switching performance of a workload between two processing circuits. The data processing apparatus has first processing circuitry which is architecturally compatible with second processing circuitry, but with the first processing circuitry being micro-architecturally different from the second processing circuitry. At any point in time, a workload consisting of at least one application and at least one operating system for running that application is performed by one of the first processing circuitry and the second processing circuitry. A switch controller is responsive to a transfer stimulus to perform a handover operation to transfer performance of the workload from source processing circuitry to destination processing circuitry, with the source processing circuitry being one of the first and second processing circuitry and the destination processing circuitry being the other of the first and second processing circuitry. During the handover operation, the switch controller causes the source processing circuitry to makes it current architectural state available to the destination processing circuitry, the current architectural state being that state not available from shared memory at a time the handover operation is initiated, and that is necessary for the destination processing circuitry to successfully take over performance of the workload from the source processing circuitry. In addition, the switch controller masks predetermined processor specific configuration information from the at least one operating system such that the transfer of the workload is transparent to that operating system. Such an approach has been found to yield significant energy consumption benefits whilst avoiding complexities associated with providing operating systems with the capability for switching applications between processing circuits.