Summary:
Currently, fan control is linear between the target temperature and max
temperature, which is far from ideal. This changes it to be proportional to the
distance between the current temperature and the two endpoints (target and max
temp). This also adds a hysteresis, so that fans keep going when the
temperature drops, for about 10 seconds, before slowing down.
Reviewers: nwhitehorn
Reviewed By: nwhitehorn
Differential Revision: https://reviews.freebsd.org/D1549
MFC after: 3 weeks
42d5cba910