Allow the system to enter sleep states in which main memory is powered and thus its contents are preserved, such as the suspend-to-RAM state (e.g. the ACPI S3 state).
This allows you to turn off the freezer for suspend. If this is done, no tasks are frozen for suspend to RAM/standby. Turning OFF this setting is NOT recommended! If in doubt, say Y.
Skip the kernel sys_sync() before freezing user processes. Some systems prefer not to pay this cost on every invocation of suspend, or they are content with invoking sync() from user-space before invoking suspend. There's a run-time switch at '/sys/power/sync_on_suspend' to configure this behaviour. This setting changes the default for the run-tim switch. Say Y to change the default to disable the kernel sys_sync().
Enable the suspend to disk (STD) functionality, which is usually called "hibernation" in user interfaces. STD checkpoints the system and powers it off; and restores that checkpoint on reboot. You can suspend your machine with 'echo disk > /sys/power/state' after placing resume=/dev/swappartition on the kernel command line in your bootloader's configuration file. Alternatively, you can use the additional userland tools available from <http://suspend.sf.net>. In principle it does not require ACPI or APM, although for example ACPI will be used for the final steps when it is available. One of the reasons to use software suspend is that the firmware hooks for suspend states like suspend-to-RAM (STR) often don't work very well with Linux. It creates an image which is saved in your active swap. Upon the next boot, pass the 'resume=/dev/swappartition' argument to the kernel to have it detect the saved image, restore memory state from it, and continue to run as before. If you do not want the previous state to be reloaded, then use the 'noresume' kernel command line argument. Note, however, that fsck will be run on your filesystems and you will need to run mkswap against the swap partition used for the suspend. It also works with swap files to a limited extent (for details see <file:Documentation/power/swsusp-and-swap-files.rst>). Right now you may boot without resuming and resume later but in the meantime you cannot use the swap partition(s)/file(s) involved in suspending. Also in this case you must not use the filesystems that were mounted before the suspend. In particular, you MUST NOT MOUNT any journaled filesystems mounted before the suspend or they will get corrupted in a nasty way. For more information take a look at <file:Documentation/power/swsusp.rst>.
Device used by the uswsusp tools. Say N if no snapshotting from userspace is needed, this also reduces the attack surface of the kernel. If in doubt, say Y.
The default resume partition is the partition that the suspend- to-disk implementation will look for a suspended disk image. The partition specified here will be different for almost every user. It should be a valid swap partition (at least for now) that is turned on before suspending. The partition specified can be overridden by specifying: resume=/dev/<other device> which will set the resume partition to the device specified. Note there is currently not a way to specify which device to save the suspended image to. It will simply pick the first available swap device.
If an arch can suspend (for suspend, hibernate, kexec, etc) on a non-zero numbered CPU, it may define ARCH_SUSPEND_NONZERO_CPU. This will allow nohz_full mask to include CPU0.
Allow the kernel to trigger a system transition into a global sleep state automatically whenever there are no active wakeup sources.
Allow user space to create, activate and deactivate wakeup source objects with the help of a sysfs-based interface.
Enable functionality allowing I/O devices to be put into energy-saving (low power) states, for example after a specified period of inactivity (autosuspended), and woken up in response to a hardware-generated wake-up event or a driver's request. Hardware support is generally required for this functionality to work and the bus type drivers of the buses the devices are on are responsible for the actual handling of device suspend requests and wake-up events.
This option enables various debugging support in the Power Management code. This is helpful when debugging and reporting PM bugs, like suspend support.
Add extra sysfs attributes allowing one to access some Power Management fields of device objects from user space. If you are not a kernel developer interested in debugging/testing Power Management, say "no".
This option will let you suspend your machine during bootup, and make it wake up a few seconds later using an RTC wakeup alarm. Enable this with a kernel parameter like "test_suspend=mem". You probably want to have your system's RTC driver statically linked, ensuring that it's available when this test runs.
Sets up a watchdog timer to capture drivers that are locked up attempting to suspend/resume a device. A detected lockup causes system panic with message captured in pstore device for inspection in subsequent boot session.
This enables code to save the last PM event point across reboot. The architecture needs to support this, x86 for example does by saving things in the RTC, see below. The architecture specific code must provide the extern functions from <linux/resume-trace.h> as well as the <asm/resume-trace.h> header with a TRACE_RESUME() macro. The way the information is presented is architecture- dependent, x86 will print the information during a late_initcall.
This enables some cheesy code to save the last PM event point in the RTC across reboots, so that you can debug a machine that just hangs during suspend (or more commonly, during resume). To use this debugging feature you should attempt to suspend the machine, reboot it and then run dmesg -s 1000000 | grep 'hash matches' CAUTION: this option will cause your machine's real-time clock to be set to an invalid time after a resume.
APM is a BIOS specification for saving power using several different
techniques. This is mostly useful for battery powered laptops with
APM compliant BIOSes. If you say Y here, the system time will be
reset after a RESUME operation, the /proc/apm device will provide
battery status information, and user-space programs will receive
notification of APM "events" (e.g. battery status change).
In order to use APM, you will need supporting software. For location
and more information, read <file:Documentation/power/apm-acpi.rst>
and the Battery Powered Linux mini-HOWTO, available from
<http://www.tldp.org/docs.html#howto>.
This driver does not spin down disk drives (see the hdparm(8)
manpage ("man 8 hdparm") for that), and it doesn't turn off
VESA-compliant "green" monitors.
Generally, if you don't have a battery in your machine, there isn't
much point in using this driver and you should say N. If you get
random kernel OOPSes or reboots that don't seem to be related to
anything, try disabling/enabling this option (or disabling/enabling
APM in your BIOS).
Per-cpu workqueues are generally preferred because they show better performance thanks to cache locality; unfortunately, per-cpu workqueues tend to be more power hungry than unbound workqueues. Enabling workqueue.power_efficient kernel parameter makes the per-cpu workqueues which were observed to contribute significantly to power consumption unbound, leading to measurably lower power usage at the cost of small performance overhead. This config option determines whether workqueue.power_efficient is enabled by default. If in doubt, say N.
Several subsystems (thermal and/or the task scheduler for example) can leverage information about the energy consumed by devices to make smarter decisions. This config option enables the framework from which subsystems can access the energy models. The exact usage of the energy model is subsystem-dependent. If in doubt, say N.