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Before, i'd a problem about changing governor for my Pi (cpu always stays at 600Mhz in every mode), after doing some tweaking, i'd already make it up to 900Mhz. However, now i'm using a power-meter to check the power consumption and even when i set cpu = 900Mhz, the consumption stays the same number as 600Mhz case.

When i lower cpu to 500Mhz or 400Mhz, it did change power consumption, but for cases >=600Mhz, nope!

I've checked current cpu freq by using both method:

$ sudo cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq

and

$ cpufreq-info -s -m (result: 600 MHz:6.12%, 900 MHz:93.88%)

they say i'm running my Pi at 900Mhz, yet no single number changes in my multi-meter screen?
(i've change several power adapter and no warning led & temp stays around 45)
Can anyone know about my problem? thank you so much for reading!

p/s: according to this site: Pi-Power under load should consume 2.1W, mine is only 1.75W (testing scenario is the same)

  • there's two different revisions of PI2B ... the most recent has the same CPU as PI3 series - just wonder if that could be the reason for the very last statement – Jaromanda X Feb 21 at 4:16
  • What kind of a power adapter do you have? If it is rated for 2.0A, it cannot draw enough current to go beyond that. – ferrix Feb 21 at 8:01
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If you're using a mains power meter, then it's quite likely the extra few milliwatts won't show. Also I would expect an idling 600MHz CPU and a 900MHz CPU to be drawing minimum power and would need a very sensitive ammeter in the USB cable to detect.

Can you try giving the Pi some CPU intensive work to do and compare again?

Other idea It would be interesting to see charts of power draw & CPU temp against CPU speed and %busy. I've not tried overclocking mine and don't want to risk it unless I have a spare, just in case it provokes an escape of magic smoke.

The RPi overclocking page at https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md shows a lot of options. Maybe you're not overclocking the bit being used by the benchmark, or you need to change several settings in proportion so you're tuning the whole system rather than just cranking one component to 11? (clutching at straws here - I'm too chicken to sacrifice my Pi to science! ).

  • yes, i'd already stressed my Pi by sysbench command as well as command stress command to make it run up to 400% cpu. And as i said, when i lowered the CPU to 400mhz, my multi-meter could detect the change in power significantly ==> i don't think the problem comes from it. – hoango27 Feb 25 at 6:17

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