The
acpitz driver supports so-called ACPI “Thermal Zones”. The temperature can be monitored by the
envsys(4) API or the
envstat(8) command.
The distinction between “active” and “passive” cooling is central to the abstractions behind
acpitz. These are inversely related to each other:
1.
Active cooling means that the system increases the power consumption of the machine by performing active thermal management (for example, by turning on a fan) in order to reduce the temperatures.
2.
Passive cooling means that the system reduces the power consumption of devices at the cost of system performance (for example, by lowering the CPU frequencies) in order to reduce the temperatures.
Only active cooling is currently supported on
NetBSD.
It should be also noted that the internal functioning of these cooling policies vary across machines. On some machines the operating system may have little control over the thermal zones as the firmware manages the thermal control internally, whereas on other machines the policies may be exposed to the implementation at their full extent.