Making power management pay off

by Chris Hamlin

January 14, 2008 —

With rising energy costs and growing awareness of the environmental costs of
power production, companies of all sizes are increasingly interested in implementing
power management and today's PCs make it easier than ever to get work done in
a more energy-efficient manner. So why isn't everyone implementing power management?
Because understanding the available settings and standards is only half the
battle.

Organizations must also consider the role of power management in the organization
and how to implement it without inconveniencing end users. If a PC causes a
software conflict or other crash when it enters or exits a low-power state,
users and executives alike are apt to call for disabling power management altogether
rather than risk data or productivity losses. Likewise, if the cost of energy-efficient
PCs is greater than the money saved from increased efficiency, few enterprises
will buy them.

How power management works

The goal of power management is to use power efficiently -- to get the most work
done per unit of energy. Part of this depends on how much power the machine
uses to do a task. If one machine requires 100 watts to do one unit of work
and another machine uses 50 watts to do the same work, the second machine will,
all things being equal, use less power.

But, power management in the real world is more complicated. Computers don't
just go on and off -- instead, they (and their individual components) have various
levels of activity and idleness. Those levels, or "states," range
from unplugged (completely off) to "asleep" to actively working. To
be highly efficient, a computer should be able to switch as quickly as possible
between the lowest practical power setting and higher, more active settings.
And, it must make that switch without impairing the ability of the machine to
perform useful work. Power management that disrupts functionality is not useful.

Generally speaking, lower-power states have greater wake latency (they take
longer to "wake up") than higher-power states (the highest power state
being "awake and working"). Industry standards go to great lengths
to define specific power states for systems and system components. These are
mostly of use to manufacturers (for more information, read Advanced
Configuration and Power Interface Specifications).

From a practical standpoint, a few system states are typically readily available
to end users:

- Idle (S0): System is awake but no active work is being done. The default
"on" state for a computer.

- Standby (S3): A sleep state (the computer appears to be off) with low wake
latency (the computer "wakes" quickly at a keystroke or other defined
event). All system context is preserved by the hardware, with the exception
of CPU caches. Some devices may still be "on."

- Hibernate (S4): A sleep state with a higher wake latency in which all devices
are powered off and platform context is saved to the hard drive.

- Soft off (S5): A state in which no platform context is saved but some power
may still be applied to the system. Requires a full system boot to wake up.

Using Windows XP as an example of typical power management settings, you can
contrast two different power settings. The power settings can be changed by
going to Power Options in the Control Panel. One case is where the machine is
set as "always on" and has the following settings:

- Power schemes: Minimal Power Management

- Turn off monitor: Never

- Turn off hard disks: Never

- System standby: Never

- System hibernates: Never

In the second case, the machine conforms to ENERGY STAR¹ default
requirements. This case uses the following settings:

- Power schemes: Minimal Power Management

- Turn off monitor: After 15 mins

- Turn off hard disks: Never

- System standby After 30 mins

- System hibernates: Never

Additionally, system components including processors, hard drives, add-in cards
(such as PCI Express cards), and displays can all have various levels of idleness
or activity. Again, in most situations, IT professionals will not apply power
management settings to components at a highly granular level. More likely, they
will set a few key variables, like when to turn off monitors after a period
of inactivity and when to turn off hard disks. Overall, while there are detailed
silicon- and code-level power management specifications, implementing power
management features at the user level is fairly straightforward.

What settings you should use varies depending on your company's needs and goals.
The ENERGY STAR program, a collaboration of the U.S.
Environmental Protection Agency and the U.S.
Department of Energy, promotes energy-efficient products and practices.
It requires that computers shipping with ENERGY STAR certification be set to
turn off monitors after 15 minutes and sleep after 30 minutes when running on
AC power.

Calculating power management ROI

One way to calculate what savings will result from implementing power management
is to use the ENERGY
STAR model. The user can input various assumptions, from the cost of each
machine to the number of hours per year the machines will be in active, idle,
sleep and off modes. This is a handy tool for getting a rough comparison between
an efficient model and a standard model.

What the ENERGY STAR model does not do is calculate how much energy a given
machine uses in a real-world setting. That might be important, especially if
you are planning to purchase a large number of PCs or just want to have more
specific numbers to help make the decision. Researchers at Intel have developed
the Energy
Efficient Performance (EEP) model as a way to estimate the actual cost of
running a PC. It uses the SYSmark benchmarking tool to perform simulated usage
runs on a real system. The model's developers specify how many runs to perform
and of what type, and give tips for taking accurate power measurements.

Here at Intel, we performed an ROI calculation using both the ENERGY STAR and
EEP models to demonstrate how one can go about using them in a real situation.
First, it is necessary to know how much power is consumed by the system in various
states. For the example system power measurements shown in Table 1, AC power
measurements (wall power) were made that include both the computer system and
the monitor. These measurements were then used with two PC energy cost models
to determine how much money can be saved under various power management scenarios.

Table 1. Example System Power Measurements¹

System State (ACPI state)	Wall Power	Notes
Active power (S0)	130 W	100% CPU utilization on both cores; monitor on
Idle case 1 (S0)	88.7 W	Hard drive spinning; monitor on
Idle case 2 (S0)	56.5 W	Hard drive spin down; monitor in sleep state
Sleep (S3)	5.4 W	WoL enabled 10 Mb link; monitor in sleep state
Standby (S5)	4.07 W	No resume on LAN; monitor in sleep state

1. Test system configuration: Intel® Core 2 Duo
processor 6400, Intel® Desktop Board DQ965 Executive Series, 1 GB DDR2 memory,
Seagate ST380815AS hard drive, Plextor PX-716A DVD-R, FSP300-60GNF power supply,
Acer KU-0355 keyboard, Acer M-UVACR1 mouse.

For this example, we will look at two methods for quantifying energy cost --
the ENERGY STAR model and EEP and various scenarios for each method. For the
ENERGY STAR model we will look at the following scenarios: always on, always
on with hard drive and monitor power management, and ENERGY STAR power management
settings. For the EEP model we will look at the always on and ENERGY STAR power
management settings scenarios.

Table 2. Power Management ROI Analysis Results

Model	Scenario	Energy Cost per 1000 systems¹
ENERGY STAR⁴	Always on	$71,619
	Always on HD and monitor power management²	$48,251
	ENERGY STAR settings³	$10,283
EEP⁵	Always on	$71,590
	ENERGY STAR settings	$15,700

NOTES:

1. Energy cost assumes a four year system lifetime and $0.0912 / kWh.

2. Hard drive and monitor set to turn off after 15 minutes of inactivity.

3. Display enters sleep mode after 15 minutes of inactivity and the system enters
sleep mode after 30 minutes of inactivity.

4. The ENERGY STAR model calculations were performed using the ENERGY
STAR savings calculator

5. The EEP model calculations were performed using the EEP
energy cost estimator

The results from the example ROI analysis in Table 2 show a clear financial
advantage to enabling power management for PCs. Something as simple as having
the hard drive and monitor power down after 15 minutes of inactivity saves $23,368
for 1000 systems during a PC lifetime of four years.

When calculating ROI related to energy-efficient computing, it is important
to factor in incentive programs as well. For example, in the United States,
ENERGY STAR partners may provide rebates or sales tax credits to support the
purchase of energy-efficient equipment. State and federal governments may also
offer incentives. The 80 PLUS
program indirectly subsidizes the cost of energy-efficient PCs by providing
incentives to manufacturers. Look for these programs before making your final
calculations -- using them can help improve the ROI picture and help energy
efficiency make better financial sense.

Another thing to remember is that your computers may already have power management
features that are not being used. Implementing them may be as simple as checking
a box or deploying a group policy. In this case, any energy savings gained from
turning on power management is money in the pocket.

Implementing power management in the enterprise

Once it is determined that there is sufficient ROI for power management
to make sense (or that the desire to be environmentally responsible overcomes
the financial burden), how do you implement it? That is, how do you set and
enforce policies, find energy-efficient equipment and develop settings that
do not harm productivity?

First, one must examine how power management can be deployed. In corporate
settings using a Microsoft Windows environment, networked computers are often
managed using Active Directory Group Policy. Microsoft has enabled all power
management settings in Windows Vista to be controlled using Group Policy. That
makes it quite easy to deploy power management settings across an organization
using that operating system.

However, when deciding to deploy those settings, one must fully understand
the potential consequences. Compatibility and interoperability are real concerns.
It is critical to thoroughly test existing network and client environments before
implementing power management settings and it is important to purchase devices,
software and drivers that work under power management.

Users themselves are probably the most challenging "component" of
IT systems to manage. Educating them -- about power management, why it is being
deployed, how it will affect them and how to avoid system issues -- is just
as important as testing hardware and software. If they know the benefit to the
company and the environment, and they know what to expect once the settings
are deployed, they are much less likely to be disgruntled when dealing with
computers that go to sleep or monitors that turn off automatically. Additionally,
many power management "conflicts" are actually caused by users trying
to force a computer to shut down or start up when it is not ready to do so.
When they understand how to tell what state the computer is in, these events
can be minimized.

One final thing that is of great concern to today's IT managers is the ability
to manage systems remotely. In many organizations, IT personnel in one location
manage servers and clients deployed elsewhere through remote management tools.
They are often concerned that they will not have remote access to computers
in a sleep state. There are several ways around this. For one thing, ENERGY
STAR specifications require that computers built for enterprise use have a "wake
on LAN" (WOL) setting available that allows a computer to be awakened with
a signal from the network. Also, many contemporary systems provide the ability
to access them even if the power is completely off or if components have failed.

Conclusion

Consumers, businesses and trade organizations are all increasingly interested
in saving energy. Because of this, PC power management has come a long way in
just a few short years. Today's operating systems and hardware make it easier
than ever to implement power management settings, while standards bodies and
industry alliances offer equipment guides and incentives to help ease the way.
To make power management a reality, two things are critical. First, calculate
ROI. Second, deploy power management settings carefully by testing systems and
educating users. If these steps are followed, almost any organization can reduce
the amount of power their PCs consume.

_________________________

1. ENERGY STAR denotes a system level energy specification, defined by
the US Environmental Protection Agency, that relies upon all of the system's
components, including processor, chipset, power supply, HDD, graphics controller
and memory to meet the specification. For more information, see http://www.energystar.gov/index.cfm?fuseaction=find_a_product.showProductGroup&pgw_code=CO

Useful Links

• Intel's
Energy-Efficient Performance - information and resources

• Advanced Configuration
and Power Interface Specifications

• ENERGY
STAR Savings Calculator

• Energy
Efficient Performance (EEP) Model

• Climate
Savers Computing Initiative

• 80 PLUS

Intel