[ltp] [PATCH] In-kernel automatic fan control

[Yury Polyanskiy]

Paul,

On Wed, 2005-11-30 at 15:18 +0000, Paul RIVIER wrote:

> I think that speed control is a smarter way to manage the fan.
> It is probably better for it's life time and reduce thermal oscillation=20
> in components.

Yeah that also bothered me at first since I read somewhere in I-net
rumors about killing your CPU/GPU with that.=20

I'm not a specialist in semiconductor technologies so I asked one
(active) professor in that area. His opinion:

1) thermal conditions affect reliability of a chip. His estimate was
that above 90 C every ten degrees double the probability of fault in
some element (non-permanent fault).

2) Thermal cycles indeed negatively affect the lifetime of a chip.
However, there are several things to note:  a) the temperatures that
worse considering are above 80-90 C again, b) the analysis is usually
done for high-performance 24x7 servers =3D> thermal cycles are present all
the time (not just during 1 hour a day when you play Quake), c) the
lifetime reduction is on the order of 10%.=20

Overall, in any case thermal cycles 45-80 C occuring randomly can't
lower laptop semiconductors' lifetime below 5-7 years. And after that we
don't care anyway.

I don't know how about you but for me that was pretty convincing to not
listen to fan noise for next 5 years ;-).

> But for properly configured laptop, there is not need to trigger at its
> maximum speed if not under heavy load.
> By and large, my point of view is :
> 1) lower values of the hysterisis values (max 50, min 44 for exemple)
> 2) over 50 : fan with speed control
> 3) if in any case even at low speed, the fan can lower temps under 44=B0C=
,=20
> stop it.

If you agree that we can put thermal cycles aside then let's assume
using hysterisis at high temps (I use 55 75). So there is indeed no need
to trigger fan at all (my fan last got turned on a week ago when I was
compiling monotone).

But even if you experience high load all the time after temperature got
above 75 C it'll take years for fan to cool it down in low speed mode.
However, it's a matter of taste. I'll try to code something reasonable
so that everyone interested could try what is better for him (5 minutes
of low speed or 1 minute of high speed).

BTW, does anyone have any observations regarding CPU load/fan speed?
Like what level (1-7) can cool what CPU load at what frequency? That
would help constructing somewhat more optimal control algorithm.

Yury.