21-06-2011, 12:09 PM
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GreenDroid
GreenDroid is a 45 nm multicore research prototype that targets the Android mobile phone software stack and can execute general-purpose mobile programs with 11 times less energy than today’s most energy-efficient designs, at similar or better levels of performance. It does this through the use of 100 or so automatically generated, highly specialized, energy-reducing cores, called conservation cores,or c-cores. GreenDroid will serve as a prototype for mobile application processors in the next five to ten years.
The GreenDroid presents a novel concept for Smartphone users: a CPU custom-designed around the apps (or perhaps types of apps) one uses the most. It has a specially built structure that can analyze a current Android phone and determine which apps, and which CPU circuits the phone is using the most. Then it can dream up a processor design that best takes advantage of those usage habits, creating a CPU that's both faster and more energy efficient.
In particular, GreenDroid attacks one of the most important realities of Moore’s Law(The number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years.) as it continues from today into the future, which we refer to as the DARK SILICON.
Energy efficiency or saving energy is the next evolution in application processors. Dark silicon is becoming the rule rather than the exception as process technologies shrink, and the problem is getting worse.To combat this we need to have a mobile application processor with specialized cores that flip dark silicon from a liability to a benefit.
DARK SILICON
Conventional chip designs in a mobile phone lose significant energy due to the presence of unused transistors called dark silicon. Dark silicon is when we have three billion transistors on our chip but we can only use 1.8 percent of them at a time, so as to squeak under the threshold of our chip's draconian energy budget. So the lights are out on vast swaths of a chip's area; hence "dark silicon”. As the transistor counts are growing faster, the underlying energy efficiency is improving, a direct consequence of this is the phenomenon of dark silicon. The dark silicon problem is directly responsible for the desktop processor industry’s decision to stop scaling clock frequencies and instead build multi-core processors. It plays an equally pivotal role in shaping the future of mobile processors as well. With each process generation, dark silicon is a resource that gets exponentially cheaper, while the power budget becomes exponentially more valuable in comparison.Dark silicon is necessary, because engineers are unable to reduce chips' operating voltages any further to offset increases in power consumption and waste heat produced by smaller, faster chips.This dark silicon limits the ultilization of the application processors to the fullest.
GreenDroid proves to be a boon to this dark silicon problem. It follows the ideology “If you fill the chip with highly specialized cores, then the fraction of the chip that is lit up at one time can be the most energy efficient for that particular task”.These highly specialized cores are known as conservation cores or c-cores.
CONSERVATION CORES
Specialized, energy-efficient processors can increase parallelism by reducing the per-computation power requirements and allowing more computations to execute under the same power budget. To pursue this goal Conservation cores, or c-cores, are specialized processors that focus on reducing energy and energy-delay instead of increasing performance. This focus on energy makes c-cores an excellent match for many applications that would be poor candidates for hardware acceleration (e.g., irregular integer codes). A toolchain is used for automatically synthesizing c-cores from application source code and demonstrating that they can significantly reduce energy and energy-delay for a wide range of applications. The c-cores support patching, a form of targeted reconfigurability, that allows them to adapt to new versions of the software they target.
