Microsoft have updated their Windows 8 development blog again and this time the topic is Power management in Windows 8.
They state 3 goals that they have for Windows 8:
- Let the hardware shine. We built Windows 8 such that the power efficiency of the hardware platform shines through, regardless of whether the system is a SoC-based Windows tablet or an SLI-equipped gaming PC. We designed our power management interfaces in a consistent, standardized way across all platforms. This allows our hardware partners and application developers to focus on their unique innovations and experiences instead of the differences in platform hardware and power management.
- Continue to deliver great battery life. Windows 7 delivered a significant reduction in power consumption and increase in energy efficiency, particularly mobile PC battery life. (In fact, you can read how we thought about it in this e7 blog post.) In Windows 8, we want to maintain that same level of efficiency on existing PCs even as we re-imagine the rest of Windows.
- Enable the smartphone power model. One of the coolest things about the System-on-Chip (SoC) platforms you’ve seen us talk about at CES and //BUILD/ is their capability to quickly enter very low-power idle states. We want to leverage that ultra-low idle power to bring the constant connectivity and instant-on features of the smartphone power model to capable Windows 8 PCs
They feel that it’s critical to use as little power as possible even when the device is idle.
To that end, they are providing 3 key innovations in Windows 8.
- The Metro style app model
- Idle hygiene
- A new run time device power management framework
Metro Style App Model
Metro is basically being designed to make it power friendly for developers allowing the suspendion of apps in the background when they aren’t needed or running.
Microsoft refer to improvements to idle activity as idle hygiene.
Most PC platforms feature processor and chipset idle states that allow the hardware platform to stop the clock or completely turn off power to parts of the silicon when they are unused. These idle states are absolutely critical to enabling long battery life, but they require a minimal residency duration—that is, you have to be idle for long enough to make the transition in and out of the idle state worthwhile in terms of power used. This is because some power is consumed on the way into and out of the idle state. Software most effectively uses these idle states when there are as few exits from the idle state as possible, and the duration of the idle state is as long as possible.
Below, they show the difference in idle durations between Windows 7 and Windows 8.
When the screen is on, they have moved the bar significantly from a maximum idle duration of 15.6ms in Windows 7 to 35% of durations longer than 100ms in Windows 8.
Runtime device power management
PCs attain their longest battery life when all devices, including the processor, storage, and peripheral devices enter low-power modes. Microsoft is looking to better coordinate this shut down across the board with Windows 8.
In Windows 8, Microsoft have 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.
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.
Another post showing that Microsoft have really put some thought into making Windows 8 power efficient.
Another win for Sinofsky.
The post was written by Pat Stemen, a program manager on the Microsoft Windows 8 Kernel team.
You can read it in full here.