What is DVFS?

DVFS (dynamic voltage and frequency scaling) raises a chip's speed and voltage for work and lowers them at rest.

1. Up for work, down for rest
DVFS (dynamic voltage and frequency scaling) steps the voltage and clock speed (frequency) up for work and down for rest. It works like the speed buttons on a desk fan.
2. Faster needs more voltage
Each speed needs a minimum voltage; below it, the switches cannot flip in time and the chip makes errors. So when speeding up, the chip raises the voltage first; when slowing down, it lowers the speed first.
3. What picks the level
The power controller inside the chip picks the level about every millisecond. It looks at the work, the temperature, the power limits and requests from the operating system (OS).
4. Each part changes level on its own
The CPU, graphics, memory and AI engines can each have their own levels. A busy part speeds up while an idle part slows down.
5. Less wasted voltage
Every chip is a little different, so a fixed voltage must cover even the weakest chip. Tuning the voltage for each chip removes most of that extra, but keeps a small safety margin.

Words to know

Frequency: Clock speed: how many times a second the clock ticks.
Voltage: The electrical push that moves current through the chip and makes its switches flip.
Level: One pair of speed and voltage that a part can run at.
Power controller: A tiny computer inside the chip that sets each part's speed and voltage.
Power limit: The most power the chip is allowed to use.
Millisecond: One thousandth of a second.
Safety margin: Extra voltage above what is needed, kept in case the work suddenly jumps.

Testers run a heavy program, then stop it. They check that each part's speed and voltage rise while it runs and fall back after it stops.

Why can't a chip run fast at a very low voltage?Think first, then tap to see the answer.

Each speed needs a minimum voltage. Below it, the switches cannot flip in time, so the chip makes errors.