I wrote:
But I think it would make more sense to have a bare metal provisioning process for misc servers which allowed smaller numbers of Intel cores per server, where that fits the application. That would improve energy efficiency without the need to deploy a new architecture.
Actually, after looking into this, I don't think it would help very much.
I had a look at ssl1, which is an idle PowerEdge 410. It has two Intel Xeon X5650 packages, i.e. 12 cores in total. According to powertop, one package is in the C6 state about 95% of the time, and the other is about 99% C6. According to the datasheet [1], this processor model should use 10W per package in C6, i.e. 20W total.
Meanwhile, the server's RAC is reporting a system power usage of 160W, which would imply that the non-CPU parts of the system are using 88% of the idle power. I don't know where all the power goes, but it looks like it isn't to the processor.
[1] http://www.intel.com/content/www/us/en/processors/xeon/xeon-5600-vol-1-datas...
-- Tim Starling