What is a power policy? In short it’s a policy of when (or not) the manageability engine (ME) should be happily humming away. It’s important because there may be times you may not want the ME to be running. For example, you don’t want the ME running while your laptop is powered off and not plugged in (otherwise you’d wonder why your battery is always dead).
AMT has had many different options for power policies over the years (I think the AMT 4.0/5.0 generations had the most options, something like 5 on desktop and 7 on mobile). For AMT 6.0, we’re down to two (so much easier!).
They look something like this:
MEBx > ME General Settings > Power Control > Intel ME ON in Host Sleep States (this is kind of a mouthful).
[ ] Mobile: On in S0
[*] Mobile: On in S0, ME Wake in S3, S4-5 (AC only)
Raise your hand if that makes sense to you... Anyone? If you find yourself asked what is S0/S3/S4-5 you’re probably not alone. These map to ACPI system states (you can read about them here: http://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface )
In reality we really only care about a few states:
- S0 – The system is powered on
- S3 – The system is sleeping
- S4 – The system has hibernated
- S5 – The system is off
- G3 – There is no power (unplugged, and battery removed if mobile)
So now, looking at the second option, we have:
ME is ON is S0 (on when the system is powered up)
ME wake in S3/S4/S5 (AC Only) (The ME is running if the system is sleeping, hibernated, or off but only if plugged in as to not drain your battery).
But what is this ME Wake?
Well the ME has its own internal power states. Basically a high power mode and a low power mode. When you are doing management stuff (KVM sessions/Getting inventory/etc) the ME is running at full speed. If you are not using the ME it can go to sleep on its own (you can configure this in the MEBx with the “Idle Timeout” settings). This mode tells the ME to go to sleep if your machine is in a lower power state which helps to save energy. In this mode then ME will ‘wake’ when it receives manageability traffic.
Each of these power policies has a unique ID configured (these have changed from generation to generation). If you are using an older setup and configuration server you may see an error when setting the power policy (depends on how the setup and configuration server sets the policy). Using the latest configuration servers and/or ISV software is always the best practice.