3 ms·
The problem is that you can’t play around with undervolting without consequences. When you reduce the voltage, the gate voltages are lower, and the drain-sourc
by klodolph 4y ago
The problem is that you can’t play around with undervolting without consequences.
When you reduce the voltage, the gate voltages are lower, and the drain-source resistance of FETs will be higher, which means higher output impedances, and slower switching times. This will not affect every part of the circuit equally—because the circuit has all sorts of different gates and cells in it. Digital ICs, for one thing, are not made out of transistors which are all the same size. Some transistors are made larger than others. So when you undervolt things, you’re changing the performance of the circuit in very difficult to predict ways. If you end up with some gate delay that is too large, you’ll get errors. If you end up with some driver transistor that can no longer drive what it is supposed to drive, you’ll get errors.
At this point in history, we have done an immense amount of fine-tuning to our IC designs, and there is not much room for fiddling with voltages. Chips are also so large and complicated that you cannot really know that you are testing the entire chip with a given workload, unless you have a lot of insight into the chip’s architecture.
Finally, any circuit which is used for some kind of trusted computing environment needs to block undervolting because undervolting has been used in various exploits to extract keys from hardware, or bypass certain protections. It’s a weird, weird world.
- haunter 4y agoWhy does the out of the box voltage is so high though? And as far as I see it is something set by the motherboard manufacturer. Like it varies to brand to brand and betwee chipsets too (Z/H/B). Chasing that +5-10% performance doesn't seem to worth that much when the power consumption and temps go so high (so more noise from the fans, more CPU fan power consumption too etc) Same with the P1/P2 limits. By default on my motherboard it was 253w/unlimited. Which is crazy when the Intel defaults are 125w/181w (at least that's publicly available on the data sheet) I at least wish Intel would show somewhere what are the default voltage numbers. Or the motherboard manufacturer's should be more "law abiding", a simple "Enforce Intel factory defaults" should be more than enough.
- toast0 4y agoReliability. Stock voltages should basically work. Too much heat is meh, but thermal throttling works. Drop the voltage too much and bad stuff happens. AMD has 'curve optimizer' which runs some tests and configures enabled boards/cpus to set a voltage offset per core. But it seems best to do that, and then give it a little more voltage to get a stable system.
- haunter 4y ago>Stock voltages should basically work Yet it's all over the place. An Asus Z790, an MSI H770, or an Asrock B760 motherboard would all have different voltages. So stock is very hard to define. Maybe there is an Intel spec but it's not really available to the public.