| # Chrome OS Power Manager Thermal Event |
| |
| powerd monitors thermal devices (e.g. fan speed, cpu throttling state) in sysfs |
| to approximately determine the thermal state of the entire device (Chromebook) |
| to provide thermal hinting to user space via [ThermalEvent]. |
| |
| There are 4 thermal states. |
| * Nominal - The device's temperature-related conditions (thermals) are at an |
| acceptable level. There is no noticeable negative impact to the user. |
| * Fair - Thermals are minimally elevated. On devices with fans, those fans may |
| become active, audible, and distracting to the user. Energy usage is elevated, |
| potentially reducing battery life. |
| * Serious - Thermals are highly elevated. Fans are active, running at maximum |
| speed, audible, and distracting to the user. System performance may also be |
| impacted as the system begins enacting countermeasures to reduce thermals to a |
| more acceptable level. |
| * Critical - Thermals are significantly elevated. The device needs to cool down. |
| |
| The thermal state are approximately similar to [NSProcessInfoThermalState]. |
| |
| When there are multiple thermal devices, the system overall thermal state is the |
| highest state of all devices. |
| |
| [NSProcessInfoThermalState]: https://developer.apple.com/library/archive/documentation/Performance/Conceptual/power_efficiency_guidelines_osx/RespondToThermalStateChanges.html |
| [ThermalEvent]: https://chromium.googlesource.com/chromiumos/platform2/system_api/+/HEAD/dbus/power_manager/thermal.proto |
