S2idle and the Nature of Laptops

You tell your laptop to “suspend to RAM.” Are you really sure that’s what your system just did? I was utterly surprised, when I purchased my current laptop (a model of the HP 15 series that was released in 2024), that things had changed since the last laptop I had bought back in 2013.¹ Power management has changed, and things smell a lot of “mobile convergence” these days.

It’s funny because using Linux shields you from one day discovering that your 10 years old PC doesn’t work anymore. Linux supports old systems by philosophy, where MacOS and Windows are picky about how old your laptop, especially laptops, is. Microsoft is more lenient on the software side of things, such that only until recently you still could run old Win16 software on modern Windows versions. When it comes to hardware, though, good luck if your system doesn’t come with UEFI and “certified” hardware, and good luck in a couple of years.

So, while my old ASUS X55C had the power management features of a laptop from 2013, this HP 15 showed me that… even “sleep” had changed. I’m not sure how I noticed that something was different; I guess it was the fact that waking up from “sleep” was super fast on this new laptop, with almost no time delay when it came to reconnect to WiFi or Bluetooth. I immediately knew where to look at and I was presented with something I had never met before:

$ cat /sys/power/mem_sleep 
[s2idle]

In the old days of regular ACPI S3 sleep, you would’ve seen a couple of different options, like shallow and deep, the latter being what we would usually call Suspend to RAM or “actual” S3. The shallow setting is for Suspend to standby. For more details about what all of this means, there’s documentation available from the Linux kernel itself explaining everything in detail.

The way the sysfs files for power management work is interesting. Files under /sys/power only show power states that your system supports. That information, obviously, comes from the firmware itself. Therefore, if I tried something like the following on my computer to put it to sleep into an actual, traditional S3 state that powers everything off except for the RAM…

# echo 'deep' > /sys/power/mem_sleep
bash: echo: write error: Invalid argument

So, my new laptop only supports a sleep state that is implemented somewhere in the motherboard (the UEFI?). The important bit about S0ix/s2idle states is that there are different levels, beyond the one that is equivalent to suspend to RAM; you actually may enter a S0i1 state just by having your laptop sitting idle with the screen off: some parts of the motherboard may enter a low-power state, some not… Deeper S0ix states will power down more parts of the hardware or make them enter deeper low-power states. Of course, this requires the Linux kernel to support requesting these states to the firmware.

If this sounds oddly familiar to how smartphones manage power, bingo. Although smartphones, as far as I know do not follow ACPI specifications, the behavior is practically the same. When you leave your smartphone sitting idle, it selective powers down components to save energy. On Android, this is called Doze.

You know what else has happened to laptops in the last couple of years? I noticed this when I got this new one. They’re significantly harder to extend, to open up, etc., if not straight impossible. I can’t even upgrade the RAM on this one. It’s a sealed box, meant to stay as is since it was shipped from the factory. If you have the skills to get inside it, you may do so, but it is not meant to be opened. My old laptop, and any old laptop, at least allowed you to change some components: I had replaced my old ASUS’s spinning hard drive with a SATA SSD drive, extended its RAM with a pair of extra modules, and replaced its battery pack. All three upgrades or repairs are hardly possible on this new HP 15.

There are many reasons why we got into this situation, Apple being an important part of it (I guess), but there’s also another side to this. If you, the vendor, can predict that the hardware will stay the same, then you are able to implement coherent power management to all components the laptop ships with. One of the issues with traditional S3 sleep, or even S4 (Suspend to disk, aka “hibernation”), was that many times hardware components entered undefined states when woken up. This wasn’t even a problem exclusive to Linux: this could happen to you on Windows as well. The reason behind this is obvious: the platform was open, you couldn’t predict whether the user was going to change or upgrade something that would break when entering a sleep state because of drivers or your firmware not being able to handle that new component correctly.

I’m under the impression that a modern laptop is much closer to a smartphone than to a desktop workstation. We’re still on a version of x86 that internally complies with the PC standard, but laptops have evolved to behave much more like our ARM-based smartphones. My HP 15 is practically a big tablet running Arch Linux. And you know what? There are improvements to take into account from this historical evolution.

I no longer suspend to disk. I know this laptop will reliable wake up every single time I ask it to suspend to idle. I know my WiFi and Bluetooth cards will resume operations immediately as soon as I wake the system up. I know there will be no graphical gitches or slow-downs either (I was plagued with these on my old ASUS, thanks to the infamous i915 driver). I’m not even getting into the improvements in battery life that come from smart charging and discharging implemented in UEFI and modern power supplies.² Suspending to disk was sort of a workaround I used to save power and time, but also had its own issues (again, the i915 driver, but sometimes also networking). Now, with this new machine, I know things will work out of the box (unless some kernel update breaks something, which is unlikely).

Convenience is mostly always good, unless it comes with ethical problems like generative AI does. Of course, everyone’s definition of convenience will be different. Arch Linux is convenient for me, but you might find Ubuntu more convenient. We all love tinkering and I guess we all also love the thrill (and frustration) of fixing an unexpected issue on our computers, but in the end of the day, we use these machines to get things done. And I’m someone who wants her computer to be up and running as fast as possible from a sleep state because I might want to write down an idea on a text editor and close the lid a minute later.

I understand the problems with closing down the platforms we use daily, though. I’m also nostalgic of the past where PCs were your hardware playground. Laptops were always more closed down than desktop PCs, but still. However, I do wonder whether we were compensating for the shortcomings of the industry back in the 90s and 00s. Gravis, from the Cathode Ray Dude YouTube channel, has repeatedly stated that the PC platform has become a “solved problem” in the last decade or so. There are no weird hardware experiments like strange PCMCIA cards, peripherals have all converged into USB devices (maybe HDMI is the only standing exception), WiFi has become practically universal (this laptop does not have an Ethernet port), we have gotten rid of SD cards and other external storage devices… I am surprised that my new laptop comes with a headphone jack. The PC in general, but probably laptops even more, have become “boring.” This is the price of having figured a technology out, I guess.