CPU dynamic scaling on NetBSD

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I know about estd for a while, that daemon “dynamically sets the CPU-frequency on Enhanced SpeedStep, PowerNow, and APCI P-States-enabled CPUs depending on current cpu-utilization” (manpage excerpt). Thing is, I’ve never seen any CPU changing from its current speed while monitoring the machdep.powernow.frequency.current sysctl.

In order to understand what was happening, I started estd with the -o flag, which outputs the CPU-frequencies as they are set. I then realized that the “ligh watermark percentage” and “low watermark percentage” default values were way too high (respectively 40 and 80) and were never reached, so the CPU speed was never changed.

With lower values, I was able to see the CPU speed increasing and lowering as expected. So I added the following line to the /etc/rc.conf file:

estd_flags="-l 5 -h 15 -a -m 800 -d"

meaning that the low watermark is set at 5 and the high watermark at 15, which were the values I’ve considered being the right ones while watching estd -o -a console output.

Since then, whenever a CPU intensive operation occurs, I can see the CPU speed rising with the following conky parameter:

CPU Frequency: ${alignr}${exec /sbin/sysctl -n machdep.powernow.frequency.current}

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