Race to Idle
Current processors are quite good about saving power when idle; so much so that many show a behavior around power saving that surprises many people. This behavior, called race-to-idle, is best explained with a simplified example: Lets take a typical commercially available processor that consumes 34 Watts when running at full speed, and 24 Watts when running at half speed and 1 Watts when idle (using frequency and voltage scaling using P-states). On this processor, we're decoding one second of a MP3 file or some HDTV media every second. This decoding takes 0.5 seconds at half speed, and, consequently, 0.25 seconds at full speed. The energy consumption for one second is
Even though the above example is simplified from reality, the same paradigm tends to hold for real systems: It's generally better to run as fast as you can so that you can be idle longer. |