For an x86 hypervisor you'd probably use the APM interface to do this. On modern x86 "hlt" also doesn't save power.
I looked into the APM stuff in Linux for a generic way to let Linux tell VM it does not need resources allocated now, but did not like what I saw. From what I can tell the wake-up from suspend state is keyboard or mouse, which does not apply well to servers. The other one is WOL but I fear the delay for starting would be heavy. Is there anything generic for the idle Linux lowering the clock speed or so that could be implemented for S/390 ?
Rob
