On Thu, Jun 11, 2009 at 09:46:58AM +0200, Jan Stary wrote:
> On Jun 10 12:09:26, Joachim Schipper wrote:
> > On Wed, Jun 10, 2009 at 11:53:39AM +0200, Jan Stary wrote:
> > > Scenario: 4.5 on MSI Wind PC, everything works. I use this machine
> > > because it is relatively low-power and quiet.
> > >
> > > The fan rotation changes with how much the CPU is used
> > > (could someone translate this into the real thing please?),
> > > without me doing anything about it on the OS level.
> > >
> > > Unless I run something heavy, such as launching mozilla, the fan keeps
> > > pretty quiet (below the level of noise that would annoy me), but still,
> > > it could be quiter. Is there a way to control the fan RPM from the OS?
> > > (Unsurprisingly, hw.sensors.adt0.fan0 is readonly.)
> >
> > This is not an answer to your query, but are you sure that turning off
> > the cooling for the CPU is a good idea? It does turn on for a reason...
> >
> > You may want to investigate hw.setperf, which may be used to put the CPU
> > in a low-power (and -performance) state. Try sysctl hw.setperf=0 (the
> > lowest possible state).
>
> Setting hw.setperf=0 indeed lower the fan rotation, but also makes
> hw.cpuspeed=191 which is almost unusable for me then ...
>
> My point is, there is, probably (please correct me), a table that says
> "with this CPU voltage/power/temperature, rotate the fan this fast".
> Where exactly is that? Can that be controlled?
I don't think there is such a table. hw.setperf can be used to reduce
the cpu speed (and you don't need to set hw.setperf=0, of course; as
noted above, look at hw.cpuspeed), but the fan is likely activated by
CPU *temperature*. Which brings us back to my first point: you probably
don't want to turn that off.
You could hack something together, of course. Use apmd -C to make the
CPU run as cool as possible unless it's actually used, and hack some
sensorsd scripts to run apm -L and apm -C as the temperature gets too
high/sufficiently low. The downside of these sensorsd scripts, of
course, is that they will necessarily throttle your CPU when you're
using it heavily.
I use something like this to make sensorsd switch the machine to
low-performance mode when it gets too hot (not related to fan speed; if
left to run at 100% utilizations for long enough, this machine will get
so hot that the BIOS will stop it to prevent damage to the CPU. I'd
rather lose a bit of performance.)
Note that this script will not take the machine out of low-power mode
when it is not connected to the mains, as I might well have set
low-power mode to extend battery life.
Joachim
sensorsd.conf:
temp:high=95C:command=/etc/sensorsd.hot %l
sensorsd.hot:
#!/bin/sh
case "$1" in
below|within)
if sysctl hw.sensors.acpiac0.indicator0 | grep -q On; then
logger -t "$0" "CPU is cool enough, ending low-performance mode"
apm -C
fi
;;
high)
logger -t "$0" "Forcing a lower CPU speed to prevent overheating"
apm -L
;;
invalid|uninitialised)
;;
*)
echo "Unknown argument $1" >&2
exit 1
esac
Joachim
