And power saving linux

Errande

Recently I got a new laptop. It is an ASUS Zenbook flip model with i7-1165G7 (4 core…). I thought about getting an AMD model, but if there is anything good about Intel these days, it is their Linux support for mobile CPU. Right after I got this laptop, I did the thing any person would do: Putting Arch Linux on it.

The bundled Windows 10 is anything but user-friendly. Upon first boot, the laptop immediately exploded. Apparently this had something to do with “Windows Update”?

Basically, I installed Linux on it. Now I can finally get my 10 hour battery life, I thought. It apparently only lasted 5 hours max. There’s no way that’s right! And so begins my journey of Linux laptop battery optimization.

Saving power for Intel CPU

Enable power saving for Intel HWP

Intel Hardware P-State, or HWP, supports managing a CPU’s power states from dedicated chips. We can order the CPU to run on lower frequencies directly from HWP.

To enable that, create /etc/tmpfiles.d/energy_performance_preference.conf , and enter the following:

w /sys/devices/system/cpu/cpufreq/policy?/energy_performance_preference - - - - power 

Set CPU governor to powersave: 7.5W

powersave ? That is a name I haven’t heard for years. Back in the days, powersave is the CPU governor that severely limits CPU frequencies to achieve “lower” power consumption. I know we need more battery life, but not that extreme, right?

In newer kernels, Intel CPU’s governor is managed by the special intel_pstate driver. As a result, powersave actually works fantastically for them! It consumes somewhat less power, while still making the system usable.

To save power by enabling powersave CPU governor, type

cpupower frequency-set -g powersave 

Or if you want a healthy balance between power and performance, you can set it to balance_power .

After that, my laptop is consuming at around 7.5W at idle. This means roughly 7 hours of idling battery life. That’s a start, albeit not a good one.

Saving power for peripheral PCIe devices: 6W

7.5W is still a big chunk of my power budget. Where did that come from? Probably all the peripheral PCIe devices. They are never properly turned off or anything. Could this be the difference between the “amazing” Windows battery life and puny Linux ones?

Fortunately, the power saver for PCIe, Active State Power Management, is supported by Linux. So we can simply enable it, and set it to power saving mode:

echo powersupersave > /sys/module/pcie_aspm/parameters/policy 

That instantly saved ~2W(!!) for me. With ~6W power usage, that means 9 hours of idling! Nice one.

Less Intel GPU power: 5.5W

Similarly, there exists some power saving features for Intel GPU.

For example, since my laptop uses Intel Xe GPU, it supports Panel Self Refresh 2/Selective Refresh. PSR2 is quite useful for 4K displays, since updating a fraction of the display instead of the whole saves more power. It is not enabled by default though. My i915 GPU also supports Frame Buffer Compression, another power saving technique.

Moreover, modern Intel GPUs require binary firmware at startup for advanced power management.

I tried with different conbinations of i915 module options, and this is what seems to be the most effective:

echo "options i915 enable_guc=2 enable_dc=4 enable_fbc=1 enable_psr=1 enable_psr2_sel_fetch=1 disable_power_well=1" > /etc/modprobe.d/i915.conf 

Wait, didn’t the title say “4W”?

I am glad you asked. 9 hours of idle battery life is like nothing compared to Apple M1. Even on Windows, this laptop would (supposedly) get ~9 hours of life during web browsing. What is going on?

To be honest, I had no idea. Intel CPU and GPU drivers are usually well optimized. 6W does not seem like a lot, since literally anything could take some power and ruin your battery life. Maybe that is what Linux users deserve?

But I refuse. Upon checking powertop , I realized that CPU’s package C-state never went below pc02 , even once. The point of having C-states is to decrease idle power usage. It should go to pc08 while idling. Common cause for this issue is, sadly, a broken PCIe ASPM implementation. Ugh.

I almost gave up at that point. Force enabling pc08 from kernel parameters did not work. And hence the mysterious 6 Watts. I was confident that it is caused by incorrect C-states.

The road to 4W: Disabling Rapid Storage

After Linux installation, my laptop could not boot up due to an issue with NVMe drivers. Apparently Intel Rapid Storage is enabled for this laptop, and I could not disable it in the BIOS. As a temporary solution, I installed vmd driver for this, then simply forgot about it completely.

What if an incorrect implementation in vmd is preventing NVMe drive from hibernation, and thus making CPU’s C-state stuck at pc2 ?

I force flashed the laptop’s BIOS, and viola! There is now an option to disable Rapid Storage.

Time for the truth. After switching Rapid Storage off in the BIOS, powertop reported ~4.5W of power consumption. And C-state is correctly lowered to pc8 when idling.

Power saving for wireless card

The wireless card, an Intel AX205, supports power saving mode. It can be enabled via another kernel parameter:

echo "options iwlwifi power_save=1" >> /etc/modprobe.d/iwlwifi.conf echo "options iwlmvm power_scheme=3" >> /etc/modprobe.d/iwlwifi.conf 

After some optimizations for its wireless card, it finally reached below 4W: 3.97W.

And it is beautiful. 15 hours of idle battery life. Even better, when the laptop is in “tablet mode”, powertop reported above 16 hours of battery life!

Does aggressive optimizations matter?

Someone might say: “Wow, 16 hours for your laptop to do absolutely nothing. I want my laptop to have maximum productivity for 5 hours.”

They do have a point. If everything on Linux is power-hungry, this 3.5 watts of power saving means nothing. So I tested it.

Prior to all these optimizations, I could use the laptop for 4 hours max during some light browsing with music. And now, 7 hours of battery life, even with an extra IDE opened. Yes, these small optimizations do matter!

(Extra) To the Extreme: Turning off Display

“But why? Why would you turn off the laptop’s screen?” To go for the last mile.

Turning off the display means iGPU can be shut down completely. In turn, the CPU can reach an even lower C-State: pc10 . It would be fun to test the idle power consumption of the motherboard.

There is also another reason: People always talk about how power efficient Raspberry Pis are. I mean, they have slow CPUs, and have considerably simpler circuit designs. In contrast, Intel systems have this huge PCB, considerably more capacitors, a fabulous 14nm fab, and 5 GHz of raw power to cook your loved ones evenly.

Would this consume more power than a small Raspberry Pi 4? Logically, yes.

Actually, I don’t know. According to this article, an idling Pi 4 consumes 4W. My Intel laptop with display on consumes 4W at idle! What if the display is turned off?

Turns out my laptop consumes ~0.5W at idle with display off and WiFi on. With WiFi off the power consumption approaches 0.3W. That’s with a whole NVMe SSD and other peripherals.

Intel really is onto something if they can put Alder Lake into the stage successfully.

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How to Configure Power Saving on Linux Mint 21

Linux Mint is famous among Linux beginners because of its free Debian-Based Linux Distribution. It is considered the best alternative to other operating systems like Microsoft Windows. While working with the system, it is necessary to manage your power usage. It saves your battery power and energy which allows the system to run for a longer time.

But when we enable power saving mode on our Linux Mint system, it directly affects our overall system performance. Most of the background apps stop running and updating. It restricts the running applications and thus the performance of the system gets down.

Still, it is good to keep your system safe by setting power management and configuring it according to your choice. You can do it on Linux Mint 21 system, press the Super key (Windows key) or click on the Menu button located at the bottom left corner of the screen:

Navigate towards the System Settings option by searching it through the search bar. When you get it, hit it:

In the System Setting screen, scroll down until you find the Power Management icon. You will find it in the Hardware category. You can also search Power Management directly by typing power on the search bar, it will save time:

Click on the Power Management icon to display its screen on the system.

There you will find 3 options. The first one will ask you to let the screen off when you’ve left the system untouched. This will save system power in this scenario, as you can set a time to turn off the screen when there is no one using it. The default set time is 30 minutes but you can change it according to your choice:

The 2nd option is to send the system into sleep mode to save power. It doesn’t affect the running applications as all the documents and applications will remain open on the system; it just moves to turn off the screen and other system parts to save the system power. It is off by default but you can enable it by clicking on it:

In the 3rd power setting option, you’re asked what should be done when the power button is pressed. It could be pressed accidentally or by yourself too. Its default setting is set to “Ask” that what you want to do, you can change it to different options like suspend, shutdown, lock screen or even you can set it to Do nothing mode:

Conclusion

Managing your power setting mode while using a system is a requirement nowadays. It helps you to save your system’s battery, and prevent you from different system faults. In the Linux Mint system, there is the by-default setting of a power management system that can also be configured according to your choice. Through this article, we have discussed in-depth details about the configuration of power saving mode in the Linux Mint 21 system.

About the author

Syeda Wardah Batool

I am a Software Engineer Graduate and Self Motivated Linux writer. I also love to read latest Linux books. Moreover, in my free time, i love to read books on Personal development.

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