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We have Raspberry PI 3B+ with Pi Touch Display and Pi camera. Today, we measured power consumption and this setup takes around 1 A with Xorg+our app and around 900 mA when Xorg is stopped and only console is running.

We would like to measure power consumption on different CPU frequencies so we tried to set different scaling governors. But we notice that regardless the set governor, the "vcgencmd measure_clock arm" still returns 1.4 GHz (even when idle while "scaling_cur_freq" returns the correct frequency) and power consumption is still same.

When scaling_governor is set to "performance", scaling_cur_freq returns correctly 1.4 GHz. When scaling_governor is set to "powersave", scaling_cur_freq returns correctly 600 MHz. When scaling_governor is set to "ondemand", scaling_cur_freq jumps between 600 and 1.4 GHz.

But "vcgencmd measure_clock arm" still returns 1.4 GHz in all of these cases.

I would not bother about returned number but unchanged power consumption makes me feel that the scaling governor does not change the frequency on CPU at all.

Is such behaviour correct?

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I found this is the bug in Raspbian kernel.

https://github.com/raspberrypi/firmware/issues/1005

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