Command processing circuitry maintaining a linked list defining entries for one or more command queues and executing synchronization commands at the queue head of the one or more command queues in list order based on completion criteria of the synchronization command at the head of a given command queue

Circuitry comprising:

• a memory to store data defining a set of one or more command queues each associated with a respective memory address space, each command queue defining successive commands for execution from a queue head to a queue tail, the commands being selected from a set of commands comprising synchronization commands and one or more other commands defining memory management operations for a given memory address space, in which completion of a synchronization command is dependent upon one or more completion criteria indicating that all commands from any of the one or more command queues which are earlier than the synchronization command in an execution order have completed;
• and
• command processing circuitry to execute the commands;
• in which the command processing circuitry is configured to maintain a linked list of entries having a list order, each entry defining a respective one of the one or more command queues, in which the command processing circuitry is configured to execute commands at the queue head of the one or more command queues, the one or more command queues being defined by prevailing entries of the linked list of entries in the list order;
• and in which, for a current occupancy of the linked list at a given stage of executing commands from the one or more command queues defined by entries of the linked list, the command processing circuitry is configured to execute a first synchronization command earliest in the list order and to detect, within that current occupancy of the linked list at the given stage, any further synchronization commands at the queue head of the one or more command queues which are defined by entries of the linked list later in the list order, the command processing circuitry applying, for any such further synchronization commands, the completion criteria of the synchronization command at the head of a given command queue, the given command queue being defined by an entry of the linked list earliest in the list order so as to treat the further synchronization commands as having been completed.