4 ms·

Why measure just the CPU and not the whole machine ?

by reportgunner 2y ago

dannyw 2y ago
Because PSUs (sadly) don't have a simple interface that transmits to your OS.
- reportgunner 2y ago
  Why do you need to transmit to your OS though ?
  - Weryj 2y ago
    Well imagine your PSU has all the metrics, now what? You need to get them somewhere for software to use.
    - reportgunner 2y ago
      Use on what, that's exactly what I was asking about in my original and subsequent question.
  - SketchySeaBeast 2y ago
    Presumably for ease of reference and integration. If you don't need your OS to see it, why not just plug your PSU into a watt meter?
    - shermantanktop 2y ago
      Use hardware to measure hardware…makes sense.
      - wongarsu 2y ago
        Especially in the current IoT boom where you can get "smart plugs" with built-in power meters for $5-$10 a piece. If you get the zigbee version you get easy-ish API access without sending the data off into the cloud. But even the Wifi cloud-enabled versions usually have a semblance of an API. I use lots of them throughout the house without any intention of ever using them to actually toggle power.
    - reportgunner 2y ago
      Yes I 100% agree and that's why I dont understand why using a software CPU Energy meter makes sense.
      - SketchySeaBeast 2y ago
        Well, that's the joy of this simplified scenario, but if you go back to the original objective, measuring the CPU's draw, you can't easily do that with a Watt meter.
- wongarsu 2y ago
  Many server PSUs can report those values. `ipmitool dcmi power reading` might give good results, but most server vendors have their own tooling that gives more detailed results. If you are into overspending on PSUs you can get similar features in consumer PSUs, for example [1]. But at that point we have completely left the realm of "simple interface". If you want to get a whole-system overview the PSU values are obviously better. But one of the biggest power consumer in many servers are the fans, and because they react to temperature sensors they always lag behind what's actually happening. That makes attributing a rise or fall in power tricky at sub-minute timescales. That's where CPU energy use is much more useful, even if it's a less complete picture. 1: https://www.thermaltake.com/toughpower-irgb-plus-850w-gold-tt-premium-edition.html https://www.thermaltake.com/toughpower-irgb-plus-850w-gold-t...
  - jeffbee 2y ago
    > because they react to temperature sensors they always lag Why don't systems drive the fans based on the VR state instead of lagging temperature readings?
    - kube-system 2y ago
      Ambient temps aren't always a constant? Nor is the end-to-end performance of the cooling solution?
      - jeffbee 2y ago
        I'm not suggesting that the fan control should be open-loop with respect to temperature, only that temperature is lagging but voltage and current are leading, so if the CPU is going to ask for a massive step change in power the platform can look at that and precharge the fans.
        kube-system 2y ago
        I guess you could, but what would you gain? You can't dissipate the heat until it reaches the heatsink anyway. And for bursty workloads you might not even know whether or not you're going to need it. The point of the thermal solution is just to keep the chip from throttling or destroying itself, and direct measurement is plenty quick enough to accomplish that.
- gradschool 2y ago
  Some do, but (sadly) only for Windows. https://www.corsair.com/us/en/explorer/diy-builder/power-supply-units/how-to-set-up-corsair-power-supplies-in-icue-4/ https://www.corsair.com/us/en/explorer/diy-builder/power-sup...
gnufx 2y ago
You don't just want to measure CPU consumption, but whole-system power is only useful for application performance if only one application of significance runs on it. I'd expect to measure it anyway for system management purposes.

Why measure just the CPU and not the whole machine ?

dannyw 2y ago

Because PSUs (sadly) don't have a simple interface that transmits to your OS.

reportgunner 2y ago
Why do you need to transmit to your OS though ?
- Weryj 2y ago
  Well imagine your PSU has all the metrics, now what? You need to get them somewhere for software to use.
  - reportgunner 2y ago
    Use on what, that's exactly what I was asking about in my original and subsequent question.
- SketchySeaBeast 2y ago
  Presumably for ease of reference and integration. If you don't need your OS to see it, why not just plug your PSU into a watt meter?
  - shermantanktop 2y ago
    Use hardware to measure hardware…makes sense.
    - wongarsu 2y ago
      Especially in the current IoT boom where you can get "smart plugs" with built-in power meters for $5-$10 a piece. If you get the zigbee version you get easy-ish API access without sending the data off into the cloud. But even the Wifi cloud-enabled versions usually have a semblance of an API. I use lots of them throughout the house without any intention of ever using them to actually toggle power.
  - reportgunner 2y ago
    Yes I 100% agree and that's why I dont understand why using a software CPU Energy meter makes sense.
    - SketchySeaBeast 2y ago
      Well, that's the joy of this simplified scenario, but if you go back to the original objective, measuring the CPU's draw, you can't easily do that with a Watt meter.
wongarsu 2y ago
Many server PSUs can report those values. `ipmitool dcmi power reading` might give good results, but most server vendors have their own tooling that gives more detailed results. If you are into overspending on PSUs you can get similar features in consumer PSUs, for example [1]. But at that point we have completely left the realm of "simple interface". If you want to get a whole-system overview the PSU values are obviously better. But one of the biggest power consumer in many servers are the fans, and because they react to temperature sensors they always lag behind what's actually happening. That makes attributing a rise or fall in power tricky at sub-minute timescales. That's where CPU energy use is much more useful, even if it's a less complete picture. 1: https://www.thermaltake.com/toughpower-irgb-plus-850w-gold-tt-premium-edition.html https://www.thermaltake.com/toughpower-irgb-plus-850w-gold-t...
- jeffbee 2y ago
  > because they react to temperature sensors they always lag Why don't systems drive the fans based on the VR state instead of lagging temperature readings?
  - kube-system 2y ago
    Ambient temps aren't always a constant? Nor is the end-to-end performance of the cooling solution?
    - jeffbee 2y ago
      I'm not suggesting that the fan control should be open-loop with respect to temperature, only that temperature is lagging but voltage and current are leading, so if the CPU is going to ask for a massive step change in power the platform can look at that and precharge the fans.
      - kube-system 2y ago
        I guess you could, but what would you gain? You can't dissipate the heat until it reaches the heatsink anyway. And for bursty workloads you might not even know whether or not you're going to need it. The point of the thermal solution is just to keep the chip from throttling or destroying itself, and direct measurement is plenty quick enough to accomplish that.
gradschool 2y ago
Some do, but (sadly) only for Windows. https://www.corsair.com/us/en/explorer/diy-builder/power-supply-units/how-to-set-up-corsair-power-supplies-in-icue-4/ https://www.corsair.com/us/en/explorer/diy-builder/power-sup...

gnufx 2y ago

You don't just want to measure CPU consumption, but whole-system power is only useful for application performance if only one application of significance runs on it. I'd expect to measure it anyway for system management purposes.