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Consider a thermal zone with one passive trip point, a cooling device with 3 states (0, 1, 2) bound to it, passive polling enabled (nonzero passive_delay_jiffies) and no regular polling (polling_delay_jiffies equal to 0) that is managed by the Step-Wise governor. Suppose that the initial state of the cooling device is 0 and the zone temperature is below the trip point to start with. When the trip point is crossed, tz->passive is incremented by the thermal core and the governor's .manage() callback is invoked. It sets 'throttle' to 'true' for the trip in question and get_target_state() returns 1 for the instance corresponding to the cooling device (say that 'upper' and 'lower' are set to 2 and 0 for it, respectively), so its state changes to 1. Passive polling is still active for the zone, so next time the temperature is updated, the governor's .manage() callback will be invoked again. If the temperature is still rising, it will change the state of the cooling device to 2. Now suppose that next time the zone temperature is updated, it falls below the trip point, so tz->passive is decremented for the zone (say it becomes 0 then) and the governor's .manage() callbacks runs. It finds that the temperature trend for the zone is 'falling' and 'throttle' will be set to 'false' for the trip in question, so the cooling device's state will be changed to 1. However, because tz->polling is 0 for the zone, the governor's .manage() callback may not be invoked again for a long time and the cooling device's state will not be reset back to 0. This can happen because commit |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.