Reducing power consumption in a fat-tree network

Communication apparatus, comprising:

• a plurality of switches, comprising leaf switches and spine switches arranged in a fat-tree network, such that the leaf switches are interconnected by links with the spine switches arranged in multiple levels, culminating in a highest level;
• and
• a network manager, which is configured to select, according to a predetermined selection order and responsively to an estimated characteristic of communication traffic to be carried by the network, a subset of the spine switches in the highest level to be active in carrying the communication traffic, and in each of the levels of the spine switches below the highest level, to select the spine switches to be active based on the selected spine switches in a next-higher level, so as to cause the network to operate so as to convey the traffic between the leaf switches via the active spine switches, while the spine switches that are not selected remain inactive.

Communication apparatus, comprising:

• a computing system comprising a fat-tree network, which comprises leaf switches and spine switches interconnected by links, and a plurality of computing nodes connected to the leaf switches;
• and
• a network manager, which is configured to receive computing jobs that are to be executed by the computing system and to schedule the jobs to run on respective groups of the computing nodes, wherein the groups are selected so as to enable one or more of the spine switches to be deactivated during execution of at least one of the jobs, and to cause the jobs to be executed on the respective groups of the computing nodes as scheduled while deactivating the one or more of the spine switches.