iMac G5: experimental thermal & cpufreq support

Benjamin Herrenschmidt benh at
Fri Sep 30 22:07:06 EST 2005

> First data on cpufreq support: Power consumption on idle for a 1600
> MHz iMac G5 is down to about 50 Watts with the powersave governor
> from about 74 Watts without voltage control (ok, display off in both
> instances).  Thanks, Ben.  U Heidelberg owes you for saving it quite
> a bit of electricity.

How did you measure it btw ? The CPU itself appears to eat about 4 watts
when idle on half speed and about 10 watts when idle on full speed. It
appears to max out at about 11W on half speed on load and about 30W on
load at full speed ,though I suppose it would be possible to write
specific code that eats more power (using altivec for example).

> For some reason the conservative and ondemand governors don't work as
> I'd expect them to from my x86 experience.  I hope I'll be able to
> look into the matter next week.

I just fixed more bugs in there, get the latest thermal control patch,
it also fixes issue with the cpufreq. Not sure it will fix your problems

> Thermal control has various little problems for me (like
> windfarm_lm75_sensor: Unknown parameter `windfarm_pid') that I don't
> have time to figure out right now, either (another todo for next
> week).

Ugh ? the lm75 sensor has nothing to do with the PID code ... What is
the exact error you get ? (compile time ? runtime ?)

>   At least my little hack
> ( still works with the new
> patches.
> Nitpick: I had to enable SMP in .config to get the cpufreq support
> built (otherwise boot_cpuid, get_hard_smp_processor_id and friends
> are undefined).  That doesn't feel quite right.

Hrm... Ok, I must admit that a !SMP g5 kernel is something I haven't
tried for a long time :) I'll have a look.

Thanks for testing !


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