1. A method comprising: determining periodically an indicia of energy expended by a first subcircuit and by a second subcircuit of a synchronous circuit during respective executions of at least one instruction, wherein one or more time periods between periodic determinations is adjusted based on aging of at least one of the first subcircuit or the second subcircuit; and directing an execution task to a subcircuit selected from the first subcircuit and the second subcircuit, wherein the subcircuit selection is based upon comparing the indicia of energy expended by the first subcircuit and by the second subcircuit with the execution performance of the first subcircuit and the second subcircuit.