obsdfreqd

Userland CPU frequency scheduling for OpenBSD

Compilation

As easy as make

Running

Run obsdfreqd as root, quit with Ctrl+C.

Installation

make install as root, enable the service using rcctl enable obsdfreqd.

Start the service with rcctl start obsdfreqd.

If you use apmd service, you have to start it either with -H or -L flag, otherwise it will start after obsdfreqd and set the performance policy to automatic and obsdfreqd will crash.

Usage

Parameters are applied when both plugged on the wall or on battery, parameters can have two values comma separated to give different values when plugged on wall and for when on battery.

• -h show usage
• -v verbose mode, CSV output if one wants to create diagrams
• -d downstepfrequency sets the steps removed every cycle when decaying, default to 100
• -i inertia sets the number of cycles after which the frequency will decay, 0 is the default
• -m maxfrequency sets the maximum frequency the CPU can reach in percent, 100% is default
• -l minfrequency sets the minimum frequency the CPU must be lowered to, 0% is default
• -r threshold sets the CPU usage in % that will trigger the frequency increase, 30% is the default
• -s stepfrequency sets the percent of frequency added every cycle when increasing, 10% is default
• -t timefreq sets the milliseconds between each poll, 300 is the default
• -T maxtemperature sets the temperature threshold under which the maximum frequency will be temporary lowered until the CPU cools down

Example:

obsdfreqd -T 90,65 will start the daemon, when power is plugged in, maximum temperature is set to 90°C and 65°C when on battery.

Explanation

The current algorithm works this way:

If CPU usage > threshold, increase frequency by stepfrequency up to maxfrequency every timefreq milliseconds and keep this frequency at least inertia cycles.

If CPU usage <= threshold, reduce frequency by downstepfrequency down to minfrequency every timefreq milliseconds when inertia reached 0. inertia lose one point every cycle the CPU usage is below threshold.

When flag -T is used, if the temperature exceeds the defined limit, the maxfrequency is decremented every cycle. When the current temperature is below the limit, the frequency limit is incremented at every cycle.

When switching from/to battery, values switch to mode specific when user defined.

What is it doing?

obsdfreqd will change the perfpolicy sysctl to manual and will change the CPU frequency by polling every often (like 100ms) the CPU load and change the frequency accordingly, the perfpolicy is set to auto upon exit.

The end goal is to provide a feature rich CPU frequency scheduler for the following use case:

• battery saving while keeping responsiveness when needed (which apm -L doesn't do)
• reduce heat or electrical coil noise when on powerplug because the new default assuming mainboard and CPU can manage itself doesn't work well
• reduce power consumption for system on powerplug while staying performant enough
• provide setings for minimum and maximum frequency available in some automatic mode (people may have $reasons to use this)

Power profiles example

The following profiles are a set of flags you can use with obsdfreqd to achieve a specific power usage. They are likely to change and be enhanced.

• battery saving but allow some limited speed: -m 50 -r 40 -t 300 (it limits frequency to 50% while going down abruptly)
• balanced: -t 150 -r 30 -d 10 -i 2 (it polls often and decay slowly over time)
• performance: -t 90 -r 25 -s 33 -i 10 (it increase fast and stay up long and polls often)

Profiles with different behavior when on battery:

• high performance plugged in / battery saving but allow some limited speed: -m 100,60 -r 25,40 -t 90,300 -d 10,100 -i 10,0
• low power/temperature when plugged in / battery saving: -m 98,50 -r 40 -t 90 -d 50,100 -i 4,0

Relation to the OpenBSD project

This is mostly a playground project so I can experiment with CPU frequency scheduling, there is no goal to import it into the OpenBSD kernel ever, but maybe I can learn here and improve the kernel code later.