Linux power savingJune 20 2020 17:55:12

As I stated in my previous post I recently bought a new laptop, a Clevo PA70ES. It's quite a power hungry beast when running on maximum settings. In this post I'll be taking you through the optimisations I've done to enable this laptop to run off of the battery for a reasonable amount of time.

The first obvious avenue is underclocking the CPU. For this there's an utility called intel-undervolt which you can just emerge on gentoo.
After a bit of playing around I ended up with the following settings in my /etc/intel-undervolt.conf:

undervolt 0 'CPU' -100
undervolt 1 'GPU' -50
undervolt 2 'CPU Cache' -100
undervolt 3 'System Agent' 0
undervolt 4 'Analog I/O' 0

Another obvious avenue is the monitor brightness. To allow the drivers to control the brightness, I had to add the following parameters to my kernel command line: acpi_osi="!Windows 2015" i915.enable_dpcd_backlight=1 . After that setting the brightness worked flawlessly.

With that configured, and intel-undervolt-loop added to my runlevel, I went on to configure two scripts to enable powersaving in KDE. Since we'll be modifying system properties these scripts will need root access, so you will have to create them add them to /etc/sudoers like so:

touch /bin/cpu_fast
touch /bin/cpu_powersave
chmod +x /bin/cpu_fast /bin/cpu_powersave

nano /etc/sudoers
ALL ALL=NOPASSWD: /bin/cpu_fast,/bin/cpu_powersave

These scripts can then be configured in KDE system settings to run whenever the power settings change:

The first script /bin/cpu_powersave calls /bin/bus_powersave, more on that later. It's main benefit is that also underclocks the CPU and enables laptop_mode. I disable a few cores - but this only results in minimal power savings and can be left out.

#!/bin/bash
sudo /bin/bus_powersave
sudo cpupower frequency-set -u 800MHz
sudo cpupower frequency-set -g powersave
echo 20 | sudo tee /sys/devices/system/cpu/intel_pstate/max_perf_pct
echo 20 | sudo tee /sys/devices/system/cpu/intel_pstate/min_perf_pct
echo  1 | sudo tee /sys/devices/system/cpu/intel_pstate/no_turbo
echo 0 | sudo tee /sys/devices/system/cpu/cpu11/online
echo 0 | sudo tee /sys/devices/system/cpu/cpu10/online
echo 0 | sudo tee /sys/devices/system/cpu/cpu9/online
echo 0 | sudo tee /sys/devices/system/cpu/cpu8/online
echo 0 | sudo tee /sys/devices/system/cpu/cpu7/online
echo 0 | sudo tee /sys/devices/system/cpu/cpu6/online
echo 0 | sudo tee /sys/devices/system/cpu/cpu5/online
echo 0 | sudo tee /sys/devices/system/cpu/cpu4/online
echo 1 | sudo tee /proc/sys/vm/laptop_mode
  
echo 350 | sudo tee/sys/devices/pci0000:00/0000:00:02.0/drm/card0

The /bin/bus_powersave script is more interesting. I ran "sudo powertop" using the following tool: PowerTOP. This displays a set of suggestions of which settings to enable. I simply created a bash script that loops through these devices and enables power management for each of these devices individually:

#!/bin/bash
  
for i in $(ls /sys/bus/usb/devices  | grep -o "[0-9]-[0-9]*" | uniq);do
  
  if [ "$(cat /sys/bus/usb/devices/$i/bDeviceClass 2>&1)" != "00" ] && #don't turn off the mouse/keyboard automatically
     [ -f "/sys/bus/usb/devices/$i/power/control" ]; then 
       echo 'auto' >/sys/bus/usb/devices/$i/power/control
   fi
done
  
#enable power management for all i2c pci and block devices
for i in $( ls /sys/bus/i2c/devices/*/device/power/control); do
   echo 'auto' > $i
done
  
for i in $( ls /sys/bus/pci/devices/*/power/control); do
   echo 'auto' > $i
done
  
for i in $( ls /sys/bus/pci/devices/*/*/power/control); do
   echo 'auto' > $i
done
  
  
for i in $( ls /sys/block/*/device/power/control); do
   echo 'auto' > $i
done
  
  
for i in $( ls /sys/class/scsi_host/*/link_power_management_policy); do
   echo 'min_power' > $i
done
  
echo '3000' > /proc/sys/vm/dirty_writeback_centisecs
echo "3000" > /proc/sys/vm/dirty_expire_centisecs
echo "80" > /proc/sys/vm/dirty_ratio
echo "20"> /proc/sys/vm/dirty_background_ratio
echo '0' > /proc/sys/kernel/nmi_watchdog

The last few lines were then added to enable the hard-disks ( SSD ) to rest between writes. This allows the laptop to conserve a little power by simply shutting them off while they're not in use.

All in all, this got my power usage down to about 19w with the Intel internal GPU, the monitor on low and the CPU down-clocked. Pretty decent for a gaming laptop. This just leaves the script to re-enable everything and make the laptop run faster on AC again:

#!/bin/bash
sudo cpupower frequency-set -u 4100MHz
sudo cpupower frequency-set -g performance
echo 100 | sudo tee /sys/devices/system/cpu/intel_pstate/max_perf_pct
echo 20 | sudo tee /sys/devices/system/cpu/intel_pstate/min_perf_pct
echo 0 | sudo tee /sys/devices/system/cpu/intel_pstate/no_turbo
echo 1 | sudo tee /sys/devices/system/cpu/cpu11/online
echo 1 | sudo tee /sys/devices/system/cpu/cpu10/online
echo 1 | sudo tee /sys/devices/system/cpu/cpu9/online
echo 1 | sudo tee /sys/devices/system/cpu/cpu8/online
echo 1 | sudo tee /sys/devices/system/cpu/cpu7/online
echo 1 | sudo tee /sys/devices/system/cpu/cpu6/online
echo 1 | sudo tee /sys/devices/system/cpu/cpu5/online
echo 1 | sudo tee /sys/devices/system/cpu/cpu4/online
echo 1 | sudo tee /sys/devices/system/cpu/cpu3/online
echo 0 | sudo tee /proc/sys/vm/laptop_mode
echo 1100 | sudo tee/sys/devices/pci0000:00/0000:00:02.0/drm/card0

This script is saved to /bin/cpu_fast and sets the maximum clock speed back to normal. It also enables all the cores and increases the iGPU's speed to it's maximum.

That's it, with these modifications this laptop can run ~4-5 hours on a single charge. I hope you enjoyed this quick write-up about Linux power management.