UC San Diego Team Conserves Smart Phone Energy with New Chip

• By Dian Schaffhauser
• 09/09/10

A group of researchers at the University of California, San Diego are working on the engineering challenge of reducing the power requirements of ever more powerful processors in smart phones by introducing specialized processors to take over some of the workload. The team's initial effort is to develop a prototype, nicknamed GreenDroid, that will work in Google Android phones. The research was presented during the HotChips symposium in Palo Alto, CA.

The problem is that with each successive generation of processor, the percentage of switches on a chip that can work at any given instant drops exponentially due to power constraints, according to "GreenDroid: A Mobile Application Processor for a Future of Dark Silicon," a presentation made by the team at the HotChips symposium. The transistor and power budgets "are no longer balanced," the researchers said; power has become a more precious commodity within devices than space.

The processing power that can't be tapped due to power limits is referred to as "dark silicon." Eventually, chips will have more dark silicon than active and chip designers will have hit a "utilization wall," the team explained. The goal of GreenDroid is to use dark silicon to "scale the utilization wall."

The researchers are testing out an approach wherein, through automated means, the common code across all of the primary applications being run by the main processor--such as common libraries--can be shuttled onto specialized processors automatically designed for specific needs. This approach of running separate circuits, called "conservation cores" or "c-cores," has resulted in dramatic power savings. The hot code--those operations called for again and again by multiple apps--runs on the c-cores, while the cold code runs on the host CPU, the researchers said.

For example, from nine applications being run on an Android phone, the researchers' c-core generator produced 21 c-cores. The use of those c-cores resulted in performance that was up to 18 times more energy efficient than running those same functions all on the main processor. The energy savings are derived by running non-cache operations; the c-cores don't have to do all of the locating, fetching, and caching demanded by the main processor.

Currently, the UC San Diego team is developing a 45 nanometer c-core prototype to demonstrate the benefits of their approach for mobile application processors. Computer science professors Michael Taylor and Steven Swanson from the Department of Computer Science and Engineering at the university's Jacobs School of Engineering are leading the project.

"Smartphones are a perfect match for our approach, since users spend most of their time running a core set of applications, and they demand long battery life. As mobile applications become more sophisticated, it's going to be harder and harder to meet that challenge," said Swanson. "Conservation cores offer a solution that exploits a resource that will soon be quite plentiful--dark silicon."

"This is an exciting time for UCSD. Our students are designing a real multicore processing chip, in an advanced technology, that is simultaneously advancing the state-of-the art in both smartphone and processor design. This marks the first of what I hope is many such chips that will come out of the UCSD research community," added Taylor.