Does locking a CPU frequency to a higher state (even OC) have any downsides?

Question

I got into an argument with a friend that thinks generally is not a good idea to manually lock a CPU to a high frequency, or even overclocking by locking the frequency, in a stable scenario. His main argument is: why would I want it to run like that, because most of the time my computer sits idle, as if a car engine is revved without moving. But from my experience, the analogy is not quite so because a CPU locked at a high frequency and locked voltage, will barely consume anymore power in idle states than a CPU that behaves in default configuration. As an example, from my experience, at idle, 4.1 GHz @ 1.35V and 1.6 GHz @ 0.6V uses roughly the same amount power.

But what about the clock cycles? Are there any advantages of having the CPU locked and ready for when the load demands high performance? Are there any disadvantages?

Wikipedia in CPU clocks states:

After each clock pulse, the signal lines inside the CPU need time to settle to their new state. That is, every signal line must finish transitioning from 0 to 1, or from 1 to 0. If the next clock pulse comes before that, the results will be incorrect. In the process of transitioning, some energy is wasted as heat (mostly inside the driving transistors).

Can this count as an advantage towards locking the frequency?

I would like to know more about this from an engineering / electrical POV.

Answer 1

... at idle, 4.1 GHz @ 1.35V and 1.6 GHz @ 0.6V uses roughly the same amount power.

This doesn't make sense to me.

The power consumption of a CPU can be thought as a sum of static and dynamic consumptions:

$$ P_T=P_{s}+P_{d} $$

And dynamic consumption is directly proportional to frequency and operating voltage:

$$ P_{d}\propto \ V^2 \ f $$

So, even if you keep the frequency constant (1.6 GHz or 4.1 GHz, doesn't matter), doubling the operating voltage (i.e. 1.35 V from 0.6 V) quadruples the dynamic consumption. For your case, unless the static consumption is high enough to neglect the dynamic consumption, which is unlikely, it doesn't seem to be possible to have the same consumption for both conditions. It's also a matter of how you measure it i.e. using a power meter to measure from wall plug (gives total system consumption) or using MCU's/mainboard's query routines (gives individual component-based measurement).

---

As for your main question, according to the two equations above, locking the frequency to a higher value basically increases the consumption at idle. This will

• increase the heat inside the chip therefore reduce lifespan
• and bring extra unnecessary noise (assuming a fan-cooled system)