CPU Frequency Scaling

[NeddySeagoon]

The default cpufreq/scaling_governor is powersave, so as distributed, the CPU clock is always 600MHz. The "on demand" works but it needs to be selected as default in the kernel or set as a part of the boot. This switches the CPU between 600MHz and 1.2GHz.

[sakaki-]

I'm ttrying to stay with default kernel config if at all possible...

Would the etc/init.d/raspi-config the settings from Raspbian be appropriate (link)? If so I can add a startup service to the image to the image to set something like:

SYS_CPUFREQ_GOVERNOR=/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
if [ -e $SYS_CPUFREQ_GOVERNOR ]; then
    echo "ondemand" > $SYS_CPUFREQ_GOVERNOR
    echo 50 > /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
    echo 100000 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate
    echo 50 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_down_factor
    echo 1 | sudo tee /sys/devices/system/cpu/cpufreq/ondemand/io_is_busy
fi

[NeddySeagoon]

I use ondemand with the default settings but its set in my kernel. Staying with the default kernel config is a good idea. It makes for ease of maintenance

[sakaki-]

Closing per your forum post here.

[leio]

You could provide your own configuration overrides, dropped into kernel/configs of the kernel source tree, and then pass that to the make defconfig_bcm* call, e.g a kernel/configs/sakaki.config file with the content

# Use ondemand by default
CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y

and then call

make bcmrpi3_defconfig sakaki.config

and it should apply the override to it.

[sakaki-]

@leio - agreed. The reason not to I guess is that 'official' prebuilt Raspbian kernels / module sets may in time become available for arm64 (as for arm) (using bcmrpi3_defconfig) and it'd be nice if we could have the option to use them. Raspbian itself sets the governor to ondemand during the boot process; on the current Raspbian image, /etc/init.d/raspi-config reads:

#!/bin/sh
### BEGIN INIT INFO
# Provides:          raspi-config
# Required-Start: udev mountkernfs $remote_fs
# Required-Stop:
# Default-Start: S
# Default-Stop:
# Short-Description: Switch to ondemand cpu governor (unless shift key is pressed)
# Description:
### END INIT INFO

. /lib/lsb/init-functions

case "$1" in
  start)
    log_daemon_msg "Checking if shift key is held down"
    if [ -x /usr/sbin/thd ] && timeout 1 thd --dump /dev/input/event* | grep -q "LEFTSHIFT\|RIGHTSHIFT"; then
      printf " Yes. Not enabling ondemand scaling governor"
      log_end_msg 0
    else
      printf " No. Switching to ondemand scaling governor"
      SYS_CPUFREQ_GOVERNOR=/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
      if [ -e $SYS_CPUFREQ_GOVERNOR ]; then
        echo "ondemand" > $SYS_CPUFREQ_GOVERNOR
        echo 50 > /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
        echo 100000 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate
        echo 50 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_down_factor
      fi
      log_end_msg 0
    fi
    ;;
  stop)
    ;;
  restart)
    ;;
  force-reload)
    ;;
  *)
    echo "Usage: $0 start" >&2
    exit 3
    ;;
esac

That's where I got the settings used in the '.start' script from. Arguably we should have a similar OpenRC/systemd service available on Gentoo.

[leio]

Well, you can still use them then, the config override just switched to ONDEMAND, if the arm64 upstream config will already be ondemand, it'll just be a no-op. Arguably it's better to set the default in kernel, so that the boot can go faster before too, not only after the init script gets ran. Though looks like raspbian fears issues with ondemand and has a shift holding thing to avoid it in case of some kind of trouble...