Reducing World of Warcraft's Power Consumption

Taiwanese researchers' special take on virtualization means far fewer servers and less energy

Image: Blizzard Entertainment

19 August 2010—Massively multiplayer online role-playing games (MMORPGs) such as World of Warcraft consume a lot of their players' time. They also consume a lot of energy, as more than a thousand servers can be required to create one game's virtual worlds. Last year, Yeng-Ting Lee, a 26-year-old online game fanatic, began to wonder if there was an easy way to reduce their energy consumption. Lee, who is a research assistant at the Institute of Information Science, Academia Sinica, in Taipei, Taiwan, says he has found a way to cut MMORPG power consumption in half. Last month he revealed the solution at the IEEE Cloud 2010 conference.

The computing needs of online gaming firms can be hard to meet. MMORPGs' hourly and daily workloads fluctuate widely, because many people don't or can't play during work hours or on weekdays, and each firm often plays host to several games at once.

Firms in the online gaming industry tend to have more computational power than they really need. One main reason is that their games use a so-called sharded architecture. Multiple identical game worlds, known as "realms" to the more than 10 million players in World of Warcraft, allow the game to be divided up into virtual worlds containing manageable populations. But servers must be capable of satisfying the largest population, even if the actual population playing in a given realm is much smaller. Such a design can be a headache, because as long as one player is active in a realm, the machine serving that realm cannot be shut down. And a nearly idle machine can still consume 60 percent of the energy of a fully loaded one.

Lee's adviser, Kuan-Ta Chen (now known as Sheng-Wei Chen), a 34-year-old assistant research fellow at the institute, is an experienced gamer. He says that the industry is desperately seeking a more cost-effective way to run their business.

Chen and Lee devised a "zone-based server consolidation strategy" to help MMORPGs reduce their power consumption. It takes advantage of the fact that players interact mostly with others situated near them within a virtual world, a property they call "spatial locality."

The researchers partitioned a game world into multiple disjoint "zones." They consider such a zone a perfect unit of computational effort that can be dispatched to whatever servers are available.

They used the zone divisions as the basis for turning a number of real servers into virtual machines. Virtualization, a strategy that is sweeping the server field, emulates one or more virtual computers within a physical one. The software installed in a virtual computer runs as it does in a physical one, and the virtual machine can be moved from one physical computer to another without causing interruption.

In Lee and Chen's system, if a game's virtual world contains n zones, it can be served by n processes. Each process can reside in its own virtual machine, or VM. VMs can be added and removed as zones fill with or empty of players, allowing the computing needs of a virtual world to scale up or down quickly and easily.

Using a set of real-life player statistics from World of Warcraft, collected over 273 days in 2006 at a Taiwan-based realm, Lee and Chen conducted a simulation of their idea. The simulation suggested that by reallocating the computing needs of each zone every hour, the number of servers needed could be reduced by 52 percent and electricity consumption by 62 percent. And it can all be done without degrading the user experience, says Chen.

"For the application in the gaming industry, we evaluate that about 30 percent of investment in servers could be saved," Chen says.

Blizzard Entertainment, World of Warcraft's creator, wouldn't comment on its server strategy or Lee and Chen's scheme. Gilbert Hsieh, technical director at Taiwan-based Gamania Digital Entertainment, says that his company, which develops and distributes online game software, will use Lee and Chen's server-consolidation strategy. "It's based on the avatar behavior in the real world. We've decide to work with the team for at least one year to learn how good the effectiveness could be when the strategy is applied on our products," Hsieh says, though he expects that virtualization might somewhat compromise the performance of the company's servers.

About the Author

Yu-Tzu Chiu is a Taipei-based reporter. In the August 2010 issue of IEEE Spectrum, she detailed Taiwan's ambitious foray into cloud computing.

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