PROCESSING QUEUE MANAGEMENT

A data processing system 2 includes multiple out-of-order issue queues 8, 10. A master serialisation instruction MSI received by a first issue queue 8 is detected by slave generation circuitry 24 which generates a slave serialisation instruction SSI added to a second issue queue 10. The master serialisation instruction MSI manages serialisation relative to the instructions within the first issue queue 8. The slave serialisation instruction SSI manages serialisation relative to the instructions within the second issue queue 10. The master serialisation instruction MSI and the slave serialisation instruction SSI are removed when both have met their serialisation conditions and are respectively the oldest instructions within their issue queues.