On Sat, 21 Dec 2013 18:01:35 -0500, ito wrote:
 > Hello Ian,
 > 
 > At 50 through 62C the dev.cpu.0.freq: 1298
 > 
 > at 70C , 1135
 > 
 > back up to 1298

Right, 1135 / 1298 ~= .875 = 7/8, so yes that's your 1.3GHz CPU dropping 
down one step for thermal control.

 >    dev.cpu.0.freq_levels: 1298/-1 1298/-1 973/-1 811/-1
 > 649/-1 486/-1 324/-1 162/-1
 > 
 >               Also directly below that:
 > 
 >    dev.p4tcc.0.freq_settings: 10000/-1 8750/-1 7500/-1 6250/-1   5000/-1
 > 3750/-1 2500/-1 1250/-1
 > 
 > I suppose that is the 8 (freq_levels) you where referring to.  Further I
 > infer that this -1 means that the BIOS has set them or does set them. 

Yes, but here the -1 indicates for freq_levels that power consumption in 
milliwatts at that freq is unknown, likely the same for p4tcc settings.

 > I set hw.acpi.thermal.tz0._PSV: 70C
 > 
 > Trying "find / acpi" to see it work.
 > 
 > While doing the above (find) the fan is on but not full out.

find(1) works disk harder than CPU as a rule, though here that command 
gets xorg about 70% busy, and keeps going for ages after hitting ^C, as 
it lists each file on the disk :)  Maybe useful: find / -name "*acpi*"

>From below:
 > PS, is this the exact command?
 > "   dd if=/dev/random > of=/dev/null     "

No, no.  I was careful to be precise, and yes a mistyped dd can be 
dangerous, and redirected to a file could indeed fill your disk.  
Fortunately that one doesn't work, invalid filename.  see dd(1).

 > I am reluctant to type anything like dd: anything: I'm not really that
 > confident with the command line.

Without your redirection it just reads from /dev/random, burning CPU, 
discarding the output, until you hit ^C .. perfectly safe.

 > After setting the PSV value it does not go above 71 when rendering
 > animation with blender.

Yeah rendering will busy the CPU (and GPU too) pretty well.  Good, so 
we know passive cooling works (in case your fan ever really packs up).

 > I will try cleaning it again, but I think I remember that I thought
 > cleaning would fix it before.

Unless you live in an extraordinarily dust-free environment, this needs 
doing with some regularity anyway.  I did mine the other day, as summer 
ambient temperatures over 30C are becoming normal here (happy solstice!)

At the temperatures you've quoted, apart from annoying fan noise, it 
doesn't seem broken to me.  How warm does it run just idling (versus 
what ambient temperature where you are)?

 > I looked at acpi_thermal, have to digest it.
 > 
 > Found the source online for freebsd acpi.

It'll be on your disk if you installed sources.

 > So I guess that I could adjust the throttling, through the process that
 > the machine uses to save power??

I wouldn't worry about that.  Are you not running powerd(8)?  As Kevin 
Oberman often points out, p4tcc is for thermal control - as we've just 
exercised - but cpufreq(4), controlled by powerd, is the way to save 
power when you don't need the CPU running at maximum frequency, which is 
likely most times.  Running it slower when idle _greatly_ reduces heat.

cheers, Ian
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