The Metro app model, idle hygiene, and a new runtime device power management framework

Nov 9, 2011 07:59 GMT  ·  By

The next major iteration of Windows introduces three innovations designed, among other things, to also cut down the power cost associated with software.

Increasing Windows 8’s efficiency in terms of power consumption, as well as that of the programs running on top of the platform, automatically generates a number of benefits for end users, from longer battery life to a reduced environmental impact, and lower energy costs.

Pat Stemen, a program manager on the Windows Kernel team, notes that Windows 8 software can singlehandedly influence power consumption, by using resources including the processor, the hard disks, RAM, etc.

The Metro style app model, idle hygiene, and a new runtime device power management framework are three answers from the software giant to the problem of software increasing power consumption, draining battery, decreasing the efficiency of Windows, while increasing costs and the impact on the environment.

Windows 8 Metro apps are suspended when not in use, which means that they’re not using any hardware resources, unless the user needs them to run. As such, the Redmond company managed to reduce the power cost associated with them as low as possible, when the Metro applications are not active.

“The Metro style application model is designed from the beginning to be power-friendly. The power management benefit is that the model makes it easy for developers to ensure their application is running only at the right time—applications in the background are suspended such that they do not consume resources and power when not in use,” Stemen said.

Another power management improvement in Windows 8 is set up to prolong the duration of idle states as much as possible.

Idle machines consume considerably less power than active computers, and Windows 8 does a better job at managing intermittent idle activity, which Stemen refers to as idle hygiene.

“When the screen is on, we’ve already moved the bar significantly from a maximum idle duration of 15.6ms in Windows 7 to 35% of our durations longer than 100ms in Windows 8! With the screen off and during Connected Standby, our idle durations are even longer, currently in the tens of seconds,” Stemen explained.

Microsoft is collaborating closely with its ecosystem partners to ensure that Windows 8 PCs offer long battery life, including through technologies shipping with the machines.

The evolution of runtime device power management implies that energy consumption efficiency gets a boost because hardware can enter low-power modes when not in use.

Stemen stresses that just a single device can cut battery life up to 25% in scenarios in which its power management features are disabled. In contrast, the device driver, working together with the Windows kernel power manager and platform firmware, contributes to increasing power management efficiency.

“For Windows 8, we’ve built a new device power framework that allows all devices to advertise their power management capabilities and integrate them with a special driver called the Power Engine Plug-in or PEP, designed for SoC systems,” Stemen noted.

“The PEP is provided by the silicon manufacturer and knows all of the SoC-specific power management requirements. This allows device drivers like our USB host controller or a keyboard driver to be built once, and still deliver optimal power management on all platforms from SoC-based PCs to datacenter servers.”

Windows 8 Developer Preview Build 8102 Milestone 3 (M3) is available for download here.