How Granola Works

Since we at MiserWare released what is now Granola (previously MicroMiser Beta) mid-January, we have had a massive influx of new users eager to try out the software. We personally think that the value of Granola is obvious and resonates well with people: free software that will save you energy with no noticeable impact in the performance of your system. Essentially, it offers energy savings for free, without affecting the user experience.

Since the release we've had several questions about what kind of energy savings one can expect. As an extension, I think people are interested in the actual technology that allows us to save energy without affecting performance. The underlying magic is a technology called dynamic voltage and frequency scaling or DVFS. It allows software running on a computer to lower the power of the CPU without turning the system off.

A good analogy is a dimmer switch on your dining room light. When you are writing a letter at the table, you need the full light to be able to see your work, but when you are relaxing with a glass of wine after dinner, you don't need the brightest available light. You turn down the dimmer to save energy (well, maybe not JUST to save energy) while you are relaxing.

DVFS works in a similar way. When your computer is working hard (for instance, when you are playing a game) the CPU needs to be at full speed so that it can work effectively. When your computer is "relaxing" (for instance, when you are browsing a web site) your CPU can "dim" itself by slowing down execution without you noticing. In the lower state, the CPU consumes less energy, thus making your computer more efficient. If you wanted to, you could switch between the "bright" and "dim" modes yourself to match your usage. In order to get the most efficient use of power in your computer system though, you would need to switch DVFS modes every time you changed your usage.

That is where Granola comes in. Using sophisticated workload modeling and prediction algorithms, Granola can determine when your computer is working and the CPU needs to be "bright" and when your computer is relaxing and the CPU can be "dim" without affecting your work. This allows Granola to automatically change DVFS modes to save energy when you can while still running at full speed when you need it.