1. Introduction §
OpenBSD 7.1 has been released with a change that will set the CPU to max speed when plugged to the wall. This brings better performance and entirely let the CPU and mainboard do the frequency throttling.
However, it may doesn't throttle well for some users, resulting in huge power usage even when idle, heat from the CPU and also fan noise.
As the usual "automatic" frequency scheduling mode is no longer available when connected to powergrid, I wrote a simple utility to manage the frequency when the system is plugged to the wall, I took the opportunity to improve it, giving better performance than the previous automatic mode, but also giving more battery life when using on a laptop on battery.
obsdfreqd project page
2. Installation §
Since OpenBSD 7.2 obsdfreqd is available as a packge. An extra important step is to remove the automatic mode in apmd which would kill obsdfreqd, you can keep apmd for its ability to run commands on resume/suspend etc...
rcctl ls on | grep ^apmd && rcctl set apmd flags -L && rcctl restart apmd
rcctl enable obsdfreqd
rcctl start obsdfreqd
3. Configuration §
No configuration are required, it works out of the box with a battery saving profile when on battery and a performance profile when connected to power.
If you feel adventurous, obsdfreqd man page will give you information about all the parameters available if you want to tailor yourself a specific profile.
Note that obsdfreqd can target a specific temperature limit using -T parameter, see the man page for explanations.
4. FAQ §
Using hw.perfpolicy="auto" sysctl won't help, the kernel code entirely bypass the frequency management if the system is not running on battery.
sched_bsd.c line shipped in OpenBSD 7.1
Using apmd -A doesn't solve the issue because apmd was simply setting the sysctl hw.perfpolicy to auto, which as explained above set the frequency to full speed when not on battery.