In some examples, a controller includes an interface to receive presence indicators associated with computer nodes, and a processor to determine, based on the presence indicators, a quantity of a set of computer nodes that are present in a system, and adjust, based on the determined quantity, phases of activity control indications provided to the computer nodes of the set of computer nodes, wherein the adjusting is to vary a first phase of a first activity control indication of the activity control indications relative to a second phase of a second activity control indication of the activity control indications.