Prior to the Intel Xeon X5500 Server Platforms*, measuring server power was done via expensive equipment and could only be performed in a discrete fashion. Unless you had tons of monitoring equipment to mash-up your power data - it was a tedious process. Now, using Intel DCM and Node Manager - you can pull multiple servers worth of power info to make some important power decisions in your datacenter.
First of all, you need to baseline your workload. If you're confident that you can replicate workload patterns then you've got a starting point. Otherwise, it's usually a good idea to start monitoring and looking for some cyclical patterns and/or common data points (time, power, thermals, etc) to keep track of.
In this scenario (like in my last blog) we're using a SQL workload which can be modified to run the CPU at high levels for a relatively set amount of time. The base workload runs for 7 min 30 seconds, as shown in the Intel DCM screencap below.
In this test case: Idle power for the 4 servers is 782W, and under load - the power increases to 1174W - which is a delta of 392W. This power increase occurs when work is given to the server and the P/T states react to the workload and increase power/voltage to the system to increase performance. Exactly what we've been used to seeing even since EIST was introduced several years ago.
Now, what I'll show you is something that may be very interesting in scale... I will power cap the servers by 20W each, and set the Intel DCM Power Policy to only allow 1095W for the 4 servers in the rack.
What is awesome here is that we can still finish the workload in the same 7 minutes 30 seconds. So essentially, we have saved 80W of power for each set of 4 servers and still get the same amount of work completed! In a large datacenter this can be HUGE in energy savings.
Let's do some quick math: 20W power savings per serer x 10,000 servers = 20kW power savings and you still get the work done. I hope I just helped some of you server admins get some new ideas on your next "I need a raise" talk with your manager
*your mileage may vary, so test your own workloads and report out!