4 ms·

First thing I did was on my 13600k was undervolting by -0,150v. The default settings (by the motherboard manufacturer) are not bad per se but basically eating s

First thing I did was on my 13600k was undervolting by -0,150v. The default settings (by the motherboard manufacturer) are not bad per se but basically eating so much power for a small performace increase. After undervolting the power consumption dropped by ~30-40% with a loss of ~5% performance. And temps also down by 10-15C. But tbh same with GPUs as well. RTX 3080. Conservative undervolting (850mv @ 1800-1850Mhz) works on most cards and with the same effect, loss of ~5% performance but power consumption down by ~30-40% + significantly cooler (10-15C) And you could go even lower if you like tinkering + got a good draw on the silicon lottery. Edit: changed to power consumption

jstanley 4y ago
How can changing the voltage change the TDP? Isn't the TDP a property of the physical design, not the operating conditions?
- pixl97 4y ago
  I think in this case it's being used as a measure of thermal performance at "100%" usage at a particular voltage. See the Wikipedia page on this and you'll see in modern processors that TDP is configurable. >TDP specifications for some processors may allow them to work under multiple different power levels, depending on the usage scenario, available cooling capacities and desired power consumption. Technologies that provide such variable TDPs include Intel's configurable TDP (cTDP) and scenario design power (SDP), and AMD's TDP power cap.
- haunter 4y ago
  Yeah maybe I'm using the wrong term here sorry for that. As far as I know the maximum wattage that the CPU can draw doesn't change by undervolting it. But the power consumption in watts at any given momement drops significantly. Changed the wording.
  - deleted 4y ago
    [deleted]
- klodolph 4y ago
  There’s some terminology being mixed up here. The "D" in TDP stands for design. It's the maximum amount of power that the device is designed to dissipate. The actual power draw is what the comment is talking about. The actual power draw will be different from TDP. The power draw is affected by operating conditions, like voltage and frequency. In a typical CMOS design, gates have capacitance and carry charge. When you apply a positive voltage to a gate, you deposit some charge into that gate from the positive rail. When you apply a negative voltage to that gate, the positive charge you previously deposited (from the positive rail) is dumped into the negative rail. This current, flowing from the positive to the negative rail, is proportional to the voltage (q = cv), proportional to the gate capacitance, and proportional to the switching frequency. The power is current multiplied by voltage. This means that power is proportional to voltage squared in these systems. (Or at least, it has a voltage squared component—this is a simplified model, and there are other things which contribute to power draw.) The switching frequency is also related to voltage. At higher voltages, the transistors are driven harder, and the gates switch faster, so you can rase the clock speed. The end result is that when you lower the voltage and frequency a little bit, you can get a large reduction in power draw.
  - haunter 4y ago
    Yeah thanks I mixed it up but your comment is more than insightful :O I'm just a lay person but I wish CPUs, or at least Intel CPUs were not tuned over that much. Or at least they should make undervolting much more accessible and open (not that it's very difficult now but it certainly should be more normal)
    - 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.
- burnte 4y ago
  Voltage in equals heat out. More voltage is more energy into the chip, more energy dissipated as heat.
650REDHAIR 4y ago
Are there any good resources for this? I built a pretty beastly machine during the pandemic, but I’ve left it all stock because it feels pretty daunting.
- haunter 4y ago
  For the GPU there is a very detailed guide here https://github.com/LunarPSD/NvidiaOverclocking/blob/main/Nvidia%20Overclocking.md https://github.com/LunarPSD/NvidiaOverclocking/blob/main/Nvi... Relevant part is the undervolting + you need MSI Afterburner and HWINFO (or your choice of software) to monitor power draw. But if you don't minmaxing then for example this video is more than enough https://www.youtube.com/watch?v=ANkR9v9HjZE&t=165s https://www.youtube.com/watch?v=ANkR9v9HjZE&t=165s Just watch the relevant part about MSI Afterburner adjusting the voltage curve. For the CPU it's all over the place because of the chipsets and motherboard manufacturers. You can do more on a Z board than on a B and it's different between for example MSI and Asus. I recommend to search around on Youtube and especially on reddit. Subs like /r/intel /r/amd /r/overclocking /r/buildapc are very useful. Even if you have a K CPU it should work with a "lesser" non-Z motherboard too, for example https://old.reddit.com/r/intel/comments/11dbq60/undervolting_13600k_with_asus_b660_motherboard/ https://old.reddit.com/r/intel/comments/11dbq60/undervolting... There is the Intel XTU app which very useful for monitoring. It depends once again on the motherboard but sometimes you can do undervolting there too, but generally it's recommended to do it in the BIOS. For example I can't do it either in XTU but whatever I change in the BIOS will show up there (like the "Core Voltage Offset") https://i.imgur.com/xHA5W6m.png https://i.imgur.com/xHA5W6m.png

jstanley 4y ago

How can changing the voltage change the TDP? Isn't the TDP a property of the physical design, not the operating conditions?

pixl97 4y ago
I think in this case it's being used as a measure of thermal performance at "100%" usage at a particular voltage. See the Wikipedia page on this and you'll see in modern processors that TDP is configurable. >TDP specifications for some processors may allow them to work under multiple different power levels, depending on the usage scenario, available cooling capacities and desired power consumption. Technologies that provide such variable TDPs include Intel's configurable TDP (cTDP) and scenario design power (SDP), and AMD's TDP power cap.
haunter 4y ago
Yeah maybe I'm using the wrong term here sorry for that. As far as I know the maximum wattage that the CPU can draw doesn't change by undervolting it. But the power consumption in watts at any given momement drops significantly. Changed the wording.
- deleted 4y ago
  [deleted]
klodolph 4y ago
There’s some terminology being mixed up here. The "D" in TDP stands for design. It's the maximum amount of power that the device is designed to dissipate. The actual power draw is what the comment is talking about. The actual power draw will be different from TDP. The power draw is affected by operating conditions, like voltage and frequency. In a typical CMOS design, gates have capacitance and carry charge. When you apply a positive voltage to a gate, you deposit some charge into that gate from the positive rail. When you apply a negative voltage to that gate, the positive charge you previously deposited (from the positive rail) is dumped into the negative rail. This current, flowing from the positive to the negative rail, is proportional to the voltage (q = cv), proportional to the gate capacitance, and proportional to the switching frequency. The power is current multiplied by voltage. This means that power is proportional to voltage squared in these systems. (Or at least, it has a voltage squared component—this is a simplified model, and there are other things which contribute to power draw.) The switching frequency is also related to voltage. At higher voltages, the transistors are driven harder, and the gates switch faster, so you can rase the clock speed. The end result is that when you lower the voltage and frequency a little bit, you can get a large reduction in power draw.
- haunter 4y ago
  Yeah thanks I mixed it up but your comment is more than insightful :O I'm just a lay person but I wish CPUs, or at least Intel CPUs were not tuned over that much. Or at least they should make undervolting much more accessible and open (not that it's very difficult now but it certainly should be more normal)
  - 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.
burnte 4y ago
Voltage in equals heat out. More voltage is more energy into the chip, more energy dissipated as heat.

650REDHAIR 4y ago

Are there any good resources for this? I built a pretty beastly machine during the pandemic, but I’ve left it all stock because it feels pretty daunting.

haunter 4y ago
For the GPU there is a very detailed guide here https://github.com/LunarPSD/NvidiaOverclocking/blob/main/Nvidia%20Overclocking.md https://github.com/LunarPSD/NvidiaOverclocking/blob/main/Nvi... Relevant part is the undervolting + you need MSI Afterburner and HWINFO (or your choice of software) to monitor power draw. But if you don't minmaxing then for example this video is more than enough https://www.youtube.com/watch?v=ANkR9v9HjZE&t=165s https://www.youtube.com/watch?v=ANkR9v9HjZE&t=165s Just watch the relevant part about MSI Afterburner adjusting the voltage curve. For the CPU it's all over the place because of the chipsets and motherboard manufacturers. You can do more on a Z board than on a B and it's different between for example MSI and Asus. I recommend to search around on Youtube and especially on reddit. Subs like /r/intel /r/amd /r/overclocking /r/buildapc are very useful. Even if you have a K CPU it should work with a "lesser" non-Z motherboard too, for example https://old.reddit.com/r/intel/comments/11dbq60/undervolting_13600k_with_asus_b660_motherboard/ https://old.reddit.com/r/intel/comments/11dbq60/undervolting... There is the Intel XTU app which very useful for monitoring. It depends once again on the motherboard but sometimes you can do undervolting there too, but generally it's recommended to do it in the BIOS. For example I can't do it either in XTU but whatever I change in the BIOS will show up there (like the "Core Voltage Offset") https://i.imgur.com/xHA5W6m.png https://i.imgur.com/xHA5W6m.png