[ltp] Re: tpfand configuration for an X200s

[Elias Oltmanns]

Henrique de Moraes Holschuh <hmh@hmh.eng.br> wrote:
> On Sun, 07 Dec 2008, Elias Oltmanns wrote:
>> Please keep in mind that there is not a trivial correlation between
>> temperature readings and fan speed. In particular, hysteresis enters
>> into it which can be easily observed on my X40. When I keep working for
>> a long time with active wlan but otherwise restricting myself to
>> lightweight tasks like reading emails, browsing the web, etc. and the
>> fan starts spinning eventually (this only happens in a reasonably warm
>> environment), then it won't stop for a very long time. On the other
>> hand, when I compile the kernel which challenges the CPU as well as the
>> HD, then temperature readings rise quickly and the fan gets into gear
>> accordingly. Quite shortly after compilation has completed, the fan
>> stops spinning at temperature readings that are well above the
>> thresholds that would have caused the fan to stop in the first scenario.
>
> Hysteresis is all and good, but what you describe is an outright bug in the
> firmware...

Sorry, I've been inaccurate there: Naturally, hysteresis only accounts
for the fact that the fan may be running or stopped at a given
temperature depending on which threshold has been reached before. The
behaviour I went on to describe in my previous email merely serves as a
demonstration that other factors than fixed temperature thresholds are
being considered in the fan control logic.

BTW, I quite agree that the specific behaviour I described above (the
first scenario, to be precise) is buggy. Sadly, Lenovo (or IBM for that
matter) hasn't bothered to fix that for a long time, probably because
people just suffer an annoyance and there is no danger of warranty
issues due to hardware damage. To be fair, I haven't checked the release
notes of EC and BIOS updates for about two years now and there is always
hope, I suppose. Due to some hiccup at ibm.com (redirection loop or some
such) I cannot check them right now.

>
> But a X40 will change the target RPM speed of the fan levels depending on
> battery state, etc.  You can see it in the ACPI DSDT.  Other ThinkPads
> (including newer X models) can't do it (from ACPI, at least).

Yes, that makes sense.

Regards,

Elias