3 ms·

What? In CMOS energy / op is constant unless you have dynamic voltage scaling. Which processors have this?

asdfasgasdgasdg 6y ago
Certainly my Ryzen 3700x has some degree of dynamic voltage scaling. You can see the voltage changing in Ryzen Master. I think intel has it too but not sure. Also, I am not sure it is correct that energy / op is constant, even at a given voltage? I'm no expert but I read about this when I was thinking about overclocking my device. At a given voltage, higher frequencies still use more energy due to the capacitance of all the components on the device. This is why overclocked energy dissipation scales super-linearly with voltage. Because you aren't just increasing the voltage you are increasing the frequency as well.
formerly_proven 6y ago
> What? In CMOS energy / op is constant unless you have dynamic voltage scaling. Which processors have this? Approximately all computer processors.
- jhallenworld 6y ago
  Yeah, I looked into this some more. High end ones seem to have it, but most MCUs do not. Anyway, there are many issues with taking advantage of this. I don't think it's very likely that you're going to get the ideal linear decrease per frequency. There are arguments to made for run fast until stop, because it reduces the effect of leakage current, see: https://semiengineering.com/is-dvfs-worth-the-effort/ https://semiengineering.com/is-dvfs-worth-the-effort/
  - formerly_proven 6y ago
    AFAIK low-power MCUs are always used in race-to-idle fashion because nothing beats <<1 µA sleep. For computer processors, DVFS isn't used like OP suggests, it's really more like Dynamic Temperature And Power Scaling (DTAPS), because it's meant to extract maximum performance from available power and thermal budget. Also while CPUs _do_ change power and frequency at >1 kHz, they're intentionally designed _not to_ downclock in the example GP gave (inter-frame idle).
kayfox 6y ago
I was under the impression that CMOS consumes energy on gate transition and not constantly, so the speed translates to more current consumption.

Certainly my Ryzen 3700x has some degree of dynamic voltage scaling. You can see the voltage changing in Ryzen Master. I think intel has it too but not sure. Also, I am not sure it is correct that energy / op is constant, even at a given voltage? I'm no expert but I read about this when I was thinking about overclocking my device. At a given voltage, higher frequencies still use more energy due to the capacitance of all the components on the device. This is why overclocked energy dissipation scales super-linearly with voltage. Because you aren't just increasing the voltage you are increasing the frequency as well.

formerly_proven 6y ago

> What? In CMOS energy / op is constant unless you have dynamic voltage scaling. Which processors have this? Approximately all computer processors.

jhallenworld 6y ago
Yeah, I looked into this some more. High end ones seem to have it, but most MCUs do not. Anyway, there are many issues with taking advantage of this. I don't think it's very likely that you're going to get the ideal linear decrease per frequency. There are arguments to made for run fast until stop, because it reduces the effect of leakage current, see: https://semiengineering.com/is-dvfs-worth-the-effort/ https://semiengineering.com/is-dvfs-worth-the-effort/
- formerly_proven 6y ago
  AFAIK low-power MCUs are always used in race-to-idle fashion because nothing beats <<1 µA sleep. For computer processors, DVFS isn't used like OP suggests, it's really more like Dynamic Temperature And Power Scaling (DTAPS), because it's meant to extract maximum performance from available power and thermal budget. Also while CPUs _do_ change power and frequency at >1 kHz, they're intentionally designed _not to_ downclock in the example GP gave (inter-frame idle).

kayfox 6y ago

I was under the impression that CMOS consumes energy on gate transition and not constantly, so the speed translates to more current consumption.