11 ms·

Undervolting can work WONDERS. Especially if you get lucky with binning. I'm running the i7 in my little 13" convertible with a ~140mV undervolt, which is the d

Undervolting can work WONDERS. Especially if you get lucky with binning. I'm running the i7 in my little 13" convertible with a ~140mV undervolt, which is the difference between unplayable and 90 pegged in DCS and War Thunder (flight sims) in VR (w/ eGPU). It's also almost an extra hour of battery life when I'm just browsing the internet or whatnot.

sleavey 6y ago
Wait, undervolting improves game performance for you?
- booi 6y ago
  hmm maybe less thermal throttling?
  - philjohn 6y ago
    And hitting higher clocks, for longer, as a result.
- Doxin 6y ago
  Might avoid hitting a thermal threshold and downclocking.
- freeqaz 6y ago
  Yes, definitely! Your laptop is generally constrained by how much heat it can push through the heat sink. If you get "lucky" you have a CPU that can remain stable at lower voltages. So it's effectively the same as an "overclock" because your laptop can turbo the core speed up for longer (or forever). Your laptop rarely runs at maximum turbo all day. It can only do that for a few hundred ms usually. It'll basically just hold the clock speed at whatever it can before hitting some specific temp (85-95c). When you undervolt, the frequency that it can "hold" at that temp threshold is higher.
  - neltnerb 6y ago
    Yeah, even with my NUC that had a pretty decent fan running at top speed I literally put a block of metal I kept in the freezer on top of it to keep it from downthrottling due to overheating. It was ridiculous that it could let itself get that hot instead of doing something more graceful.
    - copperx 6y ago
      Please share the name of the NUC so others can avoid it.
      - neltnerb 6y ago
        It's a 5th generation core i7 in the Intel NUC. It's been off the market for four years and the thermal issues were known and addressed in the intervening years to the best of my understanding. 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.
  - Geee 6y ago
    I wonder what exactly causes "instability" when overclocking/undervolting in a processor. Transistors don't have enough time to switch, but it matters where it happens. 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.
    - SomeoneFromCA 6y ago
      Lower voltage slows down recharging of the gates. Bugs in the integrated graphics can easily lock up the whole thing.
    - kalium-xyz 6y ago
- bserge 6y ago
  Of course it does. Undervolting is simply finding the lowest voltage your unit can stably work at. 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.
- ezoe 6y ago
  Many computers, especially those fan less laptop/2-in-1 tablet, doesn't have adequate cooling system. 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.
- swiley 6y ago
  IME on most portable computers it's heat dissipation that's giving you the upper bound on clock speed not the CPU's actual upper bound.
- xxs 6y ago
  of course it does - less voltage => more power headroom and less overall power, less heat dissipated => more thermal headroom. 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.
- BMSmnqXAE4yfe1 6y ago
  Voltage is an energy gap between on and off state of the transistor. There is also random noise on top of that gap. And that noise can sometimes cause the transistor to flip randomly, which results in an error. More voltage means system is more stable and has less random errors. But in gaming people often don't care if there is an error or two now and then, so they can tradeoff stability for lower power usage. Companies don't like that, because that means more technical support when programs randomly crash.
- ThePhysicist 6y ago
  It helps a bit to reduce power/thermal throttling, from my experience the effect is not very strong though (maybe 5-10 % at most I'd say). If your CPU gets thermally throttled a lot it's more likely that you have a faulty or underdimensioned heat sink, in that case I'd try to apply better thermal paste and/or ensure the heat sink properly connects to the CPU. My Alienware throttled the CPU a lot due to overheating because they didn't apply the thermal compound right during fabrication (and seemed to use cheap compound with low conductivity), applying better thermal compound fixed that problem reliably, while undervolting the CPU did almost nothing in that case.
- necheffa 6y ago
  A lot of laptops are built with pretty lack luster thermal design. 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.
dataflow 6y ago
Did you use "lucky" here sarcastically, or do you actually need to be lucky with binning to be able to undervolt without issues? (I thought that was a concern with overclocking?)
- londons_explore 6y ago
  The same issues occur with both.
- jchw 6y ago
  Undervolting goes hand in hand with overclocking. The goal is higher clocks. The enemies are stability and heat. Undervolting reduces heat but the impact on stability depends on the silicon lottery. For mobile chipsets, undervolting at the same clocks is a nice performance uplift because of the reduced heat (on a system that undoubtedly does not have the best heat dissipation.) 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.
  - mehrdadn 6y ago
    Thanks!
- magicalhippo 6y ago
  Roughly, the transistors in a chip can have more or less internal resistance (Rds) due to impurities and variations during production. There's no way to know from one chip to the next until you try them. 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 https://en.wikipedia.org/wiki/Junction_temperature [2]: https://en.wikipedia.org/wiki/Ohm%27s_law https://en.wikipedia.org/wiki/Ohm%27s_law [3]: https://en.wikipedia.org/wiki/MOSFET https://en.wikipedia.org/wiki/MOSFET [4]: https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873 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 https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873
Maken 6y ago
Extra battery life would be nice. It has always been a problem with Linux on laptops.
- calpaterson 6y ago
  For anyone struggling with this, look at the TLP project which is a package in most distros that makes (I think pretty anodyne) changes to improve power consumption/battery life. Not uncommon to get 50% improvements straightaway after installing it. https://linrunner.de/tlp/ https://linrunner.de/tlp/
necheffa 6y ago
I replaced the thermal paste on my laptop and no longer thermal throttle. Didn't even get fancy with exotics, just regular Arctic MX-4.

sleavey 6y ago

Wait, undervolting improves game performance for you?

booi 6y ago
hmm maybe less thermal throttling?
- philjohn 6y ago
  And hitting higher clocks, for longer, as a result.
Doxin 6y ago
Might avoid hitting a thermal threshold and downclocking.
freeqaz 6y ago
Yes, definitely! Your laptop is generally constrained by how much heat it can push through the heat sink. If you get "lucky" you have a CPU that can remain stable at lower voltages. So it's effectively the same as an "overclock" because your laptop can turbo the core speed up for longer (or forever). Your laptop rarely runs at maximum turbo all day. It can only do that for a few hundred ms usually. It'll basically just hold the clock speed at whatever it can before hitting some specific temp (85-95c). When you undervolt, the frequency that it can "hold" at that temp threshold is higher.
- neltnerb 6y ago
  Yeah, even with my NUC that had a pretty decent fan running at top speed I literally put a block of metal I kept in the freezer on top of it to keep it from downthrottling due to overheating. It was ridiculous that it could let itself get that hot instead of doing something more graceful.
  - copperx 6y ago
    Please share the name of the NUC so others can avoid it.
    - neltnerb 6y ago
      It's a 5th generation core i7 in the Intel NUC. It's been off the market for four years and the thermal issues were known and addressed in the intervening years to the best of my understanding. 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.
- Geee 6y ago
  I wonder what exactly causes "instability" when overclocking/undervolting in a processor. Transistors don't have enough time to switch, but it matters where it happens. 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.
  - SomeoneFromCA 6y ago
    Lower voltage slows down recharging of the gates. Bugs in the integrated graphics can easily lock up the whole thing.
  - kalium-xyz 6y ago
bserge 6y ago
Of course it does. Undervolting is simply finding the lowest voltage your unit can stably work at. 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.
ezoe 6y ago
Many computers, especially those fan less laptop/2-in-1 tablet, doesn't have adequate cooling system. 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.
swiley 6y ago
IME on most portable computers it's heat dissipation that's giving you the upper bound on clock speed not the CPU's actual upper bound.
xxs 6y ago
of course it does - less voltage => more power headroom and less overall power, less heat dissipated => more thermal headroom. 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.
BMSmnqXAE4yfe1 6y ago
Voltage is an energy gap between on and off state of the transistor. There is also random noise on top of that gap. And that noise can sometimes cause the transistor to flip randomly, which results in an error. More voltage means system is more stable and has less random errors. But in gaming people often don't care if there is an error or two now and then, so they can tradeoff stability for lower power usage. Companies don't like that, because that means more technical support when programs randomly crash.
ThePhysicist 6y ago
It helps a bit to reduce power/thermal throttling, from my experience the effect is not very strong though (maybe 5-10 % at most I'd say). If your CPU gets thermally throttled a lot it's more likely that you have a faulty or underdimensioned heat sink, in that case I'd try to apply better thermal paste and/or ensure the heat sink properly connects to the CPU. My Alienware throttled the CPU a lot due to overheating because they didn't apply the thermal compound right during fabrication (and seemed to use cheap compound with low conductivity), applying better thermal compound fixed that problem reliably, while undervolting the CPU did almost nothing in that case.
necheffa 6y ago
A lot of laptops are built with pretty lack luster thermal design. 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.

dataflow 6y ago

Did you use "lucky" here sarcastically, or do you actually need to be lucky with binning to be able to undervolt without issues? (I thought that was a concern with overclocking?)

londons_explore 6y ago
The same issues occur with both.
jchw 6y ago
Undervolting goes hand in hand with overclocking. The goal is higher clocks. The enemies are stability and heat. Undervolting reduces heat but the impact on stability depends on the silicon lottery. For mobile chipsets, undervolting at the same clocks is a nice performance uplift because of the reduced heat (on a system that undoubtedly does not have the best heat dissipation.) 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.
- mehrdadn 6y ago
  Thanks!
magicalhippo 6y ago
Roughly, the transistors in a chip can have more or less internal resistance (Rds) due to impurities and variations during production. There's no way to know from one chip to the next until you try them. 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 https://en.wikipedia.org/wiki/Junction_temperature [2]: https://en.wikipedia.org/wiki/Ohm%27s_law https://en.wikipedia.org/wiki/Ohm%27s_law [3]: https://en.wikipedia.org/wiki/MOSFET https://en.wikipedia.org/wiki/MOSFET [4]: https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873 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 https://techweb.rohm.com/knowledge/si/s-si/03-s-si/4873

Maken 6y ago

Extra battery life would be nice. It has always been a problem with Linux on laptops.

calpaterson 6y ago
For anyone struggling with this, look at the TLP project which is a package in most distros that makes (I think pretty anodyne) changes to improve power consumption/battery life. Not uncommon to get 50% improvements straightaway after installing it. https://linrunner.de/tlp/ https://linrunner.de/tlp/

necheffa 6y ago

I replaced the thermal paste on my laptop and no longer thermal throttle. Didn't even get fancy with exotics, just regular Arctic MX-4.