insomniad is a daemon implementing Linux's autosleep mechanism in user space. This allows additional policy to factor into the decision to suspend the system beyond the kernel's built-in wakeup sources.
This is useful for AC powered devices where the overhead of entering suspend is more influential than the power saved by going to sleep as soon as possible.
Linux's /sys/power/autosleep feature takes into account wakeup sources which
come from drivers in the kernel and user space wake locks. When no wakeup
sources are active, the system will immediately suspend.
It may be useful to take into account more factors than explicit locks and events. For example, accounting time since the last wakeup source was active (hysteresis) can help reduce thrashing on systems that are slow to suspend. Without the ability to globally adjust the timeout, every wakeup source's timeout would need to be modified. This isn't feasible as the wake locks and wakeup sources are spread across various applications and drivers, respectively.
- Configurable time since last event before initiating sleep
- systemd integration
The mechanism to implement the policy in user space while still racelessly
accounting for kernel wakeup sources is provided by the
/sys/power/wakeup_count API. Read more at
Documentation/ABI/testing/sysfs-power