Zeb Hering 4dffbb070c Let the fan settle downward on a re-assert ...

A symmetric deadband catches the fan on the way up and holds it there:
on iz-pve0 under load, 17 of 20 samples ran at 38% while the curve
wanted 34-36%, and nothing would bring it down until the request fell a
full 8 points. Damping was turning into a permanently louder machine.

A re-assert may now settle the speed downward to the current request.
Upward moves still require a full deadband crossing, so the drift this
was built to prevent cannot come back - covered by a test.

Verified under a live migration: settled 38 -> 36 on the first
re-assert, then one change in ten minutes while the request wandered
36-42, CPU stable at 66-69c and disks a degree cooler.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

2026-08-28 22:33:38 -07:00

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