I'm just saying that linux does not do a great job of gracefully limiting CPU power to avoid a lower BIOS level limiter kicking in and performing worse than if it just throttled down a bit earlier.
If there's an error in e.g. floating-point unit, it would just cause random errors in the output, but the game would probably keep running. That might be completely fine, if it's rare and you could undervolt just that unit a lot. Especially in somewhere in the graphics pipeline, where it would just generate visual noise. Also, I think energy consumed / heat is proportional to voltage squared, so it has a big effect.
The processor circuitry does not only consist of transistors dedicated to the datapath, a significant amount of transistors are used to control the datapath. If control transistors are faulty there is no guarantee about the processor behavior.
Also, I don't know about Intel cpu protections, but in modern secure hardware we include dedicated circuits for power/clock glitch detection. The glitch detection circuit is designed with a higher sensibility to power/clock fault than the rest of the circuit, this way its avoids that clock/power faults affect the integrity of the circuit output.
Not x86, but in college a series of courses used a battery powered embedded system with a Motorolla 68HC11. When the batteries ran low, conditional branches would never branch, which was very confusing. Everything else seemed to work fine though.
I had a Surface Book 2 that was particularly bad for this, I think because it uses the same connector as older versions, and it could not supply enough power. Undervolting seemed to help quite a bit.
Within that envelope, the CPU can boost up to its max turbo frequency when needed.
The only result of undervolting on modern CPUs is lower temperature; performance actually goes up as the processor still aims to hit its set TDP/TPL limits.
Lower voltage = higher clocks for longer on all Intel CPUs that can be undervolted. I believe it's the same for new AMDs, but I haven't had the chance to test one.
You're basically fine tuning your pet rock - some silicon is higher quality and can do better than the stock voltages that were set for thousands/millions of units out of the factory.
If CPU was used too much, it instantly reach the temperature threshold, then forced down clock and stall kicks in to save the CPU, repeat the cycle.
Which way do you prefer? endless cycle of 60fps for 10 seconds followed by shuttering for 10 seconds, OR stable 20fps.
If the silicon doesn't need the voltage, more voltage is only harmful. I can run my skylake alike laptop at -170mV offset (which is borderline golden chip), stable at prime 95 and whatnot. Prime95 runs below 70C.
Less voltage means less waste heat. If you can lower voltage without lowering clock speed, you'll be able to maintain turbo boost longer instead of constantly thermal throttling.
Not my first recommendation but it is a valid strategy.
Overvolting is also useful for overclocking; at a point it can help increase stability. But generally I think you want to hit a point at which you are getting the highest clocks with the lowest voltage that is still stable.
If it has less internal resistance it will generate less heat for the same amount of work. Semiconductors are constrained by the maximum junction temperature[1], and CMOS logic chips like modern processors primarily consume power when switching.
So there's a thermal limit to how fast they can switch. Thus having lower internal resistance can allow you to clock higher (switch more often) before reaching the thermal limit.
However, when switching they act as varying resistors, and the amount of power dissipated in any resistor depends on the square of the applied voltage (P = V^2/R).
So if you can run your chip on a lower voltage, it will dissipate a lot less energy when switching, thus allowing you to switch faster before being thermally limited.
When overclocking, you ask the transistors to switch faster. To turn a MOSFET[3] transistor on or off, you need to transfer a certain amount of charge (aka electrons) into or out of the gate. The faster you can transfer the charge (more electrons per second ie the higher the current) the quicker the transistor turns on. And the way to do that is to increase the voltage[2]. So overclockers tend to bump up the voltage when going for the super-high clocks. But as you see from above that causes a massive increase in heat, thus requiring significantly more cooling.
I'm no semiconductor expert though, so I might got some of this wrong, but I hope I got the essence right. Also I'm not sure if the impurities and such that lead to the variability of the internal resistance is related to the ones affecting the ability to undervolt. Is it mainly the threshold voltage or?
There are other aspects as well though, I assume the parasitic elements[4] play a role as well, especially when overclocking.
[1]: https://en.wikipedia.org/wiki/Junction_temperature
[2]: https://en.wikipedia.org/wiki/Ohm%27s_law
[3]: https://en.wikipedia.org/wiki/MOSFET
[4]: https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873
[4]: https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873