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Microsoft Details Power Smart Windows 8 Development
According to a recent post on Building Windows Blog, Pat Stemen, a program manager on Kernel team with Microsoft explains why battery life and power consumption continue to be some of the most important topics in the computing industry.Three goals were kept in mind while engineering Windows 8 power management:
Let the hardware shine: Windows 8 was built in such a way 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.
Continue to deliver great battery life: Like Windows 7, in Windows 8 too, the same level of efficiency is maintained as on existing PCs even as development of Windows continues.
Enable the smartphone power model: One of the coolest things about the System-on-Chip (SoC) platforms is their capability to quickly enter very low-power idle states. Efforts are being made to bring that ultra-low idle power to bring the constant connectivity and instant-on features of the smartphone power model to capable Windows 8 PCs.
Windows 8 features three key innovations to improve how software influences power consumption—the Metro style app model, idle hygiene, and a new runtime device power management framework.
The Metro style application model
One of the new power management innovations in Windows 8 is the Metro style application model. 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.The Metro style application model and the underlying WinRT support background activity through a new set of capabilities called background tasks.Background tasks make it easy to perform background activity in a power-friendly fashion.
Software can have dramatic influence on power consumption even without consuming a lot of resources through intermittent idle activity. A new term is used for 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.
Figure below shows the difference in idle duration between the Windows 7 and Windows 8.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.
Runtime device power management
PCs attain their longest battery life when all devices, including the processor, storage, and peripheral devices enter low-power modes. Almost every device in the modern PC has some kind of power management technology, and runtime device power management determines how we use those technologies seamlessly without impact to the user experience. A really good example of runtime device power management is dimming the automatic display after a timeout in Windows 7.For Windows 8, a new device power framework is built 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.
Let the hardware shine: Windows 8 was built in such a way 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.
Continue to deliver great battery life: Like Windows 7, in Windows 8 too, the same level of efficiency is maintained as on existing PCs even as development of Windows continues.
Enable the smartphone power model: One of the coolest things about the System-on-Chip (SoC) platforms is their capability to quickly enter very low-power idle states. Efforts are being made to bring that ultra-low idle power to bring the constant connectivity and instant-on features of the smartphone power model to capable Windows 8 PCs.
Windows 8 features three key innovations to improve how software influences power consumption—the Metro style app model, idle hygiene, and a new runtime device power management framework.
The Metro style application model
One of the new power management innovations in Windows 8 is the Metro style application model. 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.The Metro style application model and the underlying WinRT support background activity through a new set of capabilities called background tasks.Background tasks make it easy to perform background activity in a power-friendly fashion.
Software can have dramatic influence on power consumption even without consuming a lot of resources through intermittent idle activity. A new term is used for 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.
Figure below shows the difference in idle duration between the Windows 7 and Windows 8.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.
Runtime device power management
PCs attain their longest battery life when all devices, including the processor, storage, and peripheral devices enter low-power modes. Almost every device in the modern PC has some kind of power management technology, and runtime device power management determines how we use those technologies seamlessly without impact to the user experience. A really good example of runtime device power management is dimming the automatic display after a timeout in Windows 7.For Windows 8, a new device power framework is built 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.
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