Hysteresis feature doesn't seem to work or just really confusing

[catsuperberg]

Hysteresis sounds like a simple and useful feature. But it isn't clear what seems to be the use of hysteresis as it is implemented.

Is it there to create a stairstep effect for people with gradual fan curves?

With the option like "Hysteresis only applies on the way down" and hysteresis set to 10 degrees I'd expect following behavior:

• i have a graph with 20% below 50 degree temp and 40% above that mark
• as soon as temp goes over 50 the fan ramps to 40%
• when the load is lowered some and the temp is 45 degree the fan is still at 40% as the temp isn't 10 degrees below 50
• when the temp hits 39 degree the fan goes down to 20% until the 50 is reached again

But for now, with a simple stairstep graph it just either shift immediately between fan speed levels no mater if temps go up or down, or if you set response time to something high it lags both on the way up and down.

It would be great to see the implementation like this or another feature that enables this. I find it irritating when fans change speed be it gradually or with distinct steps and for the loads that are shifting right around the point you set on the graph it would be great to force higher RPM until it actually significantly dropped.

[Rem0o]

Hysteresis is simply the degree of change required from the last change. If the last point of change was 48 degree, it will be centered around that point. Be aware that hysteresis is ignored at the limits of your graph ( first and last point ). That option can be disabled.

Hysteresis doesn't care about the shape of your graph, so if you expect the hysteresis to always applies exactly at a specific point, like around a staircase point, this may be why you got confused. It won't be "centered" around your 50 degree point.

The type of behavior you describe looks a lot more like a trigger fan curve. Look it up.

[Rem0o]