What does the operating system do in ordder to manage power in current HPC clusters ? What are the functionalities embedded in current HPC clusters in order to save power
Not every cluster is the same, and the power management varies as widely as any other feature. Some use very rudimentary techniques to save a little power, others shutdown nodes that aren't used, or other actions that save more significant amounts of power.
If you have questions about a specific model of cluster we may be able to help more, but open ended questions like this will not have a good answer.
Well, if you look at a typical HPC cluster, the compute nodes will be standard x86 servers running Linux. So you might ask, what can Linux do to save power on x86 hardware? Well, there's all these ACPI C-states and whatnot that can be used to put processors into some kind of sleep mode based on inactivity, or clock down the processors and so forth.
Then, some batch schedulers have features allowing idle nodes to be shut down, and then when there is work to do, the scheduler can boot these nodes (via IPMI, ILO, or some other remote management system).
In practice, we haven't really looked into any of that. Why? Well, our clusters run more or less constantly at 90+% load. If there at some point is lots of idle nodes, some clever geezer will see his/her chance and submit a mile long list of jobs to the queue; Problem solved. :)