[Linux] Improving battery life + reducing heat generation of ultra-thin laptops with 6+ physical-core CPU

Preface

This post discusses a combined method to extend battery life of high-end laptops with 6-core or 9-core Intel CPUs while reducing the heat generation at the same time. The method sets CPU peformance differently depending on the power source (AC or battery) and uses TLP as a frontend for automation.

Summary

• Intel p_state driver
• Completely software method (will not harm your hardware)
• Intel processors with 6+ physical cores
• Adjust perf for dynamic frequency downscaling, thus significantly reduce power consumption + heat
• Disable unused CPU cores to maximize battery (not necessary for laptops with high-capacity battery)
• Disable unused hardware in battery mode (ethernet/bluetooth..)
• Can be used in tandem with other methods such as reducing CPU operating voltage (undervolt) or changing thermal conductivity substance (repaste)

Test Spec

• Hardware: System76 oryx pro 4, Dell precision mobile workstation 7560, Dell XPS 15.
• Distro: Tested with Ubuntu 16.04.6, Ubuntu 18.04.2, Pop!OS 20.04 with latest kernels.

Battery:

15" built-in display @ 144Hz: Embedded 4 Cells Polymer battery pack – 55Wh (57.1Wh max)    

Results:

powerstat is used to evaluate the battery discharge rate of different profiles.

Method	Discharge rate	CPU Temp.	Load	Method Description
1	11.64W	38-40C	Light load: gnome-system-monitor, powerstat, powertop, background: Google Chrome (1 tab), psensor	Intel GPU + this combined method + backlight display @ 15%
2	16.41W	41-43C	Light load: gnome-system-monitor, powerstat, powertop, background: Google Chrome (1 tab), psensor	Intel GPU + TurboBoost disable + perf:19%-50% + original config + backlight display @ 15%
3	23.56W	48-50C	Light load: gnome-system-monitor, powerstat, powertop, background: Google Chrome (1 tab), psensor	nvidia GPU (GTX 1070 max-q) + TurboBoost disable + perf:19%-50% + original config + backlight display @ 15%
4	9.11W	36C	No load (idle)	Intel GPU + this combined method + backlight display @ 15%

Note: I used system76-power to disable the nvidia GPU.

While powertop reports the current recharge rate per process at the moment, it is not accurate to use it to measure the total power consumption. A tool that statistically measures the power consumption over a long period of time (7-10 minutes) will produce more reliable results. In this end, we use powerstat.

From the evaluation, method 1 can help oryx4 laptop last about 5 hours under light load (I often got 5h - 5.2h). While method 4 can prolong the laptop battery to 6 hours in idle (a convenient test case for different profiles, not practical use case).

Prerequisites

• Intel p_state driver

Optional (but recommended)

• TLP to automate the setting below.
• powertop (one should not run powertop --auto-tune at start-up to avoid conflict with TLP).

Method Explained

To extend battery life, I use the following combined methods:

• Enable dynamic frequency down-scaling based on performance profile in Intel p_state.
• Disable unnecessary services/processes that adversely affect the battery life.
• Automate the process with tlp.
• Reduce the number of operational cores in battery mode. (manually run after startup)
• Tuning with powertop.

Enable dynamic frequency down-scaling (runtime)

Instead of manual underclocking the CPU, I use a dynamic method to down-scale the CPU frequency by setting the maximum and minimum performance allowed in AC and battery.

Require: an active intel p_state driver (power governor = powersave(default)) (to check: cat /sys/devices/system/cpu/intel_pstate/status)

Battery Mode:

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

Explain: Set the maximum performance allowed equal to 19% of the highest possible performance. The Intel p_state driver will down-scale the CPU frequency accordingly. This can be executed at run-time.

• max-performance <- 20/100 is equivalent to set maximum CPU freq @ 800MHz (intel i7-8750H)
• min-performance <- 20/100 is equivalent to set minimum CPU freq @ 800MHz (intel i7-8750H)
• Turbo Boost <- disable

Note: You should experiment and try different max_perf_pct value and see what best suits your need. Suggest: if you are using in battery mode, try first with a value between 20-30%. If you are on AC, try a value between 70-90%.

AC Mode:

echo 80 | 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

Explain: Set the maximum performance allowed equal to 80% of the highest possible performance. The Intel p_state driver will down-scale the CPU frequency accordingly. This can be executed at run-time.

• max-performance <- 80/100 is equivalent to set maximum CPU freq @ 3400MHz (intel i7-8750H)
• min-performance <- 20/100 is equivalent to set minimum CPU freq @ 800MHz (intel i7-8750H)
• Turbo Boost <- enable

With these setting, the maximum CPU temperature is 40C (light load + no TurboBoost) on battery and 75-80C (high load + TurboBoost) with AC plugged in. Refer to this post for the relation between frequency and temperature.

To automate the process, I use TLP. You can find my TLP config here

Please read thru the config before applying. Also, I encourage you to peruse the tlp document here

Disable unnecessary processes

Disable Bluetooth (started with TLP at startup)

To disable bluetooth when on battery, change the following line in your TLP config:

DEVICES_TO_DISABLE_ON_STARTUP="bluetooth"

Disable Ethernet (runtime)

Ethernet consumes huge energy when it is used (12-14W) and considerable energy (0.5-1W) when it is not used/idle. To turn off your ethernet, refer to ifconfig for the ethernet interface name, then kill it

sudo ifconfig enp4s0 down

Note: ethernet could be on idle (i.e. no cable hooked up), but powertop would report it as in full utilization.

Refer to the bash script (execute after restart on battery): here

Disable unused CPU cores (runtime)

I found out that I never utilized all my CPU cores in battery mode. Since my goal was to keep my laptop's battery from draining, I never ran any computationally expensive programs without an AC plugged. Therefore, it is helpful for me to disable few CPU cores on battery mode. It hasn't introduced any perceived performance drop since I only ran simple programs such as VI text editor, 4 or 5 Chrome tabs, LibreOffice, etc.

To disable 4/6 physical cores in i7-8750H (don't worry, they will become online if you explicitly enable them back on or after restart)

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

Replace echo 0 by echo 1 if you want to turn these CPU cores back on.

Refer to the bash script (execute after restart on battery) here.

Tuning with powertop (runtime)

• Often it requires a calibration powertop --calibrate on battery for an extended period of time before you can start to tune. You only need run this once.
• Run powertop --auto-tune to let powertop tweak the bad processes that are eating your battery.
• Refer to reference.
• This should be done manually. Do not run powertop --auto-tune at startup to avoid conflict with TLP.

Fix sluggish USB devices after running powertop

powertop usually tends to over tune all peripheral devices on battery. This can make our USB devices less responsive. To this end, we need to manually tell powertop not to adjust it.

For example, I have a Logitech wireless usb mouse which becomes sluggish after powertop --auto-tune kicks in. There are two main parts in a wireless mouse communication, the transmitter in the mouse and a receiver that hooks up to the usb port on the PC. To tell powertop not to tweak the power consumption for my mouse, do as follows:

• Enter powertop: sudo powertop
• Navigate to tab Tunables, find the entry related to the Logitech USB receiver or your device of interest. The current tuning status is marked as Good (not really) since powertop has tuned it.
• We want to tell powertop to stop meddling in our mouse surfing business. To this end, we will select the highlighted entry (using the up/down buttons on your keyboard) and press enter to change its status from Good to Bad. Note that Bad does not indicate the highlighted device is malfunctioning or has gone rouge (power consumption-wise). It's just a way powertop tells us this device is not tuned.
• My wireless usb mouse has now come back to life.

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Hope it helps.