TMON is a kernel tool for monitoring and tuning the kernel's thermal subsystem. In announcing the latest work on the tool, its creator Jacob Pan describes the work as:
Increasingly, Linux is running on thermally constrained devices. The simple thermal relationship between processor and fan has become past for modern computers.
As hardware vendors cope with the thermal constraints on their products, more sensors are added, new cooling capabilities are introduced. The complexity of the thermal relationship can grow exponentially among cooling devices, zones, sensors, and trip points. They can also change dynamically.
To expose such relationship to the userspace, Linux generic thermal layer introduced sysfs entry at /sys/class/thermal with a matrix of symbolic links, trip point bindings, and device instances. To traverse such matrix by hand is not a trivial task. Testing is also difficult in that thermal conditions are often exception cases that hard to reach in normal operations.
TMON is conceived as a tool to help visualize, tune, and test the complex thermal subsystem.
For those wanting more information on TMON, see the Linux kernel mailing list. The tool amounts to just over 2,000 new lines of code.