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Comment by rcoder | Hacker News Reader

FWIW I'm regularly able to get ~12 hours on a charge on my PBP with normal terminal and qutebrowser or epiphany sessions running. That's closer to 3W under load, not 5W at idle.

Also, while power usage does go up a bit when the CPU is more fully loaded, it definitely doesn't jump up to 30+ watts like my ThinkPad does.

The Rockchip SoC in the PBP isn't impressive compared to the ARM chips going in current-gen high-end smartphones, but the max TDP isn't anywhere near what an Intel or AMD laptop chip cranks up to.

That also means a truly fanless computer with a monolithic, user-replaceable battery.

There's are certainly workloads where a faster, symmetric multicore x86 chip will win on computer per watt, but it's not as cut-and-dry a win in real-world usage on a laptop as it might be on (say) a heavily-loaded server.

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So, this got me curious. I pulled up my now 5 year old Skylake dell laptop, and did some quick measurements.

The "pure idle" draw is around 2.47 watts drawn from the battery with the brightness set to half.

When watching a 1080p youtube video fullscreened, the power consumption levels out at around 5 watts, again at half brightness.

If your workload is very light, there won't be much of a difference. Running mostly terminal emulators and lightweight desktop software, your biggest power consumer will likely be the screen, and most LCDs will be similar.

But if you're running heavy software like Slack or Teams (which some don't have the option to avoid, sadly), then power-per-watt becomes relevant, as running your 30 watt system for 0.5 seconds uses fewer joules of energy than pushing your 5 watt system for 4 seconds.

The rub is that a lot of that heavy software will eat up as many system cycles as the OS will give it -- which annoyingly means that once you have a bunch of tabs open in a browser, that 30 watt processor will probably stay nailed at its TDP.

However, you can manually set limits on the CPU. If I limit this skylake's max clock to 900MHz, I can play Minecraft at slightly reduced settings pretty smoothly while only drawing 7-8 watts.

It's all in what you need. If your primary goal is to reduce electricity usage, "cpupower frequency-set --max <x>" your CPU down to its lowest clock, and you're set.

(none of this is meant to diss Pine64 or ARM -- only I think getting one to be eco friendly/power efficient may be misguided, depending on your use case)

Hi,

thanks for your input, it's greatly appreciated. I'm quite new to considering my power consumption, so indeed I may still do naive choices. I only based it on the reputation of ARM for being more energy efficient, and the observation that ARM devices indeed run longer with a full battery charge (but there may indeed be a lot of secondary variables explaining it).

I'm curious : how do you measure the consumption of electricity in watts? Is there a tool meant for that?

Looking back, I was being a bit too cynical and dismissive. There are of course other factors in a device being eco-friendly, and in practice hotter chips will tend to use more power unless restrained.

On my intel laptops, I used "powertop" to measure power consumption as reported by the battery. Powertop is an intel specific tool, but I think most batteries will have an entry in linux's sysfs. Here it's under "/sys/class/power_supply/BAT0", where two files "voltage_now" and "current_now" list the voltage and current in microvolts and microamperes.

  [eery@darkshire ~]$ cd /sys/class/power_supply/BAT0
  [eery@darkshire BAT0]$ cat current_now
  269000
  [eery@darkshire BAT0]$ cat voltage_now
  8423000

So 269,000 µA x 8,423,000 µV is about 2.266 watts.

Measuring while connected to mains/AC power will probably need some kind of physical device to measure the current being pulled by the charger, sadly. Only server grade hardware seem to have built in current meters :(

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