Case Study—Measuring Processor Energy Consumption

Submitted by BDTI on Mon, 07/12/2004 - 18:00

Energy consumption is a chief concern for many digital signal processing applications, especially for portable applications where battery life is paramount. In these applications, an accurate understanding of energy consumption is critical to processor selection and to system design. Unfortunately, many obstacles hinder comparisons of processors' energy consumption.

One key problem is that vendors usually report power consumption, not energy consumption. Calculating energy consumption—which is typically more useful—requires knowing both the power consumption and the execution time for the task at hand. But it can be difficult to project execution times for key application tasks.

Another challenge stems from each vendor including different components in its power figures. For example, some vendors include on-chip peripherals and off-chip I/O in their power measurements, but others do not. This is a major problem: peripherals and I/O often consume as much power as the core and on-chip memory.

Energy efficiency projections are even more complicated for processors that use advanced power-management features such as aggressive standby modes and voltage scaling. Using such features can lead to significant energy-efficiency gains, but it is often difficult to predict how well an application will be able to exploit these features. As a result, estimating the benefit of these features can be very tricky.

These shortcomings in vendor-provided data suggest that system designers might benefit from measuring processor energy consumption themselves. However, accurately measuring energy consumption is a tricky, time-consuming task. System designers must consider many factors in order to create a realistic test scenario, and they must control many variables when measuring energy consumption.

Over the past ten years, BDTI has performed hands-on benchmarking of the energy consumption of a variety of processors with the cooperation of major processor vendors. The expertise gained from these studies allows BDTI to provide realistic, consistent analysis of processor energy consumption.

BDTI is currently planning a new hands-on study that will build on this expertise. This study will test processors' energy consumption in realistic conditions and will test the effectiveness of advanced features such as voltage scaling. To learn more about this forthcoming study, please contact Jeremy Giddings at BDTI (giddings@BDTI.com).

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