Power management with suspend for current hardware - TUXEDO Computers

Linux distributions use processes in the background to control various aspects of power management. This also includes how the device behaves after the lid of a notebook is closed. At user level, the user sets the desired behaviour for TUXEDO OS in the system settings under power management. These settings are then implemented via firmware.

Overall, this is a complex issue, as there are many components that need to work together seamlessly to ensure successful standby operation. In addition, Microsoft has introduced the new mode Modern Standby in 2012, which in the beginning was called Connected Standby and has subsequently been adopted by Intel and AMD.

In this article, we explain the current state of affairs, as there are always customer enquiries regarding the various standby models. We also discuss some of the problems associated with this complex technology.

Standby models

In the past, three standby models in particular were used to reduce the energy consumption of notebooks to varying degrees when the lid was closed. Intel defined these models as follows:

• Name: Suspend-To-Idle
• ACPI status: S0
• Label: s2idle

This state is a pure software idle state of the system. It allows to save more energy compared to idle mode by freezing the user area and putting all I/O devices (peripheral devices used for input/output purposes) into a power-saving state.

• Name: Suspend-to-RAM
• ACPI status: S3
• Label: deep

This traditional standby model causes the computer to switch off the CPU and all power consumers of the device, while the data in the RAM is retained. The path to hibernation takes a little longer than with S0, as the computer waits until all components are switched off. However, the Intel Core Ultra CPUs no longer support S3.

• Name: Suspend-to-disk
• ACPI Status: S4
• Label: disc

This state offers the greatest energy savings and works in a similar way to suspend-to-RAM, but writes the memory contents to the swap of the hard disk so that the RAM does not consume any energy to retain the data as it does with S3. When waking up, the memory contents are loaded back into RAM. Suspend-to-disk requires a swap file, which is either created as a partition during installation or later as a swap file. The swap should be at least as large as the installed RAM. If you have little disk space available, a swap with 2/3 of the RAM is probably sufficient, as its content is compressed during suspend-to-disk.

Modern Standby

Intel and AMD have been supporting the new Modern Standby (MS) standard developed by Microsoft, which is gradually replacing suspend-to-RAM,for some years now. MS uses a step-by-step process to maintain the battery’s state of charge as far as possible. Components are switched off when they are not in use. MS is designed to improve the situation by offering the same energy savings as S3, but with a drastically reduced wake-up time.

• Name: Modern Standby (MS)
• ACPI status: S0ix
• Label: s2idle (was previously used as an identifier for S0)

Unfortunately, this mode still has some issues. Some users report that the battery is draining heavily in idle mode or that there are problems waking up the components. These problems affect Windows, macOS and Linux. However, the sleep behaviour of S0ix is improved under Linux with every kernel update.

It is important to understand that the S0 model formerly known as s2idle now lives on under the same name as S0ix. So if you see s2idle in a current notebook, it is Modern Standby.

Intel and AMD no longer officially support S3 deep since Intel Gen 11 and Ryzen 6000. Although Intel still supports S3 in some current CPUs, it cannot be guaranteed that S3 will function properly. For the Intel P- and U-processors of the 12th and 13th generation used in many modern notebooks, S3 is no longer supported. However, the S- and H-processors still support S3.

You can verify this on your device by entering cat /sys/power/mem_sleep. If deep is displayed in square brackets, your CPU is using S3 mode. It is not known how long this will be the case.

Unfortunately, this does not guarantee that S3 will work satisfactorily. The mainboard manufacturers have the final say here, as not all components such as WiFi modules or NVME/SSDs support S3 equally well. Anything that is not standard after installation is untested and cannot be supported by us.