[RFC] Patch to enable temperature ceiling in powerd

[Ian Smith]

On Mon, 4 Feb 2008, Alexandre "Sunny" Kovalenko wrote:
 > On Thu, 2008-01-31 at 05:35 -0500, John Baldwin wrote:
 > > On Wednesday 30 January 2008 05:56:19 pm Alexandre "Sunny" Kovalenko wrote:
 > > > Some time ago I have put together patch for powerd, which allows user to
 > > > specify the temperature threshold at which powerd will lower CPU
 > > > frequency no matter what the load was at the time. I recently had to
 > > > adapt it to the 7.0-PRERELEASE for someone with the overheating laptop,
 > > > which got me to think that it might be useful for someone else yet.
 > > > 
 > > > Basic idea is fairly simple -- check temperature in TZ0 and, if it has
 > > > reached certain value, either override frequency with the lowest
 > > > available (in the case of 'max' setting) or change idle time to 100% and
 > > > let adaptive algorithm decrease frequency gradually.
 > > > 
 > > > I imagine it also could be poor man's substitute for the low noise
 > > > acoustic policy ;)
 > > > 
 > > > If there is an interest, I will go ahead and submit a PR, otherwise it
 > > > will live in the mail archives for someone to find. Any comments,
 > > > suggestions or criticisms are welcome.
 > > > 
 > > > Temperature threshold (in Celsius) could be set by means of '-T' command
 > > > line option (as in '-T 60').
 > > 
 > > A couple of suggestions:
 > > 
 > > - I would make the default temperature 0 instead of 200 and just disable the
 > >   feature altogether if it is set to 0 (i.e. don't read the current
 > >   temperature and don't do any checks if it is 0).
 > > - I would allow the temperature to be specified in either C, K or F with a
 > >   suffix to indicate the scale.  (e.g., "80C", "120F", "300K")
 > > - I would let the thermal zone name be configurable with a default of "tz0".
 > >   (e.g. "-z tz3").  You would then snprintf the sysctl mib name that gets
 > >   passed to sysctlbyname(3).
 > > 
 > John,
 > I have attached new patch, implementing your suggestions (some of these
 > were already implemented by Ian Smith and sent to me privately). I have
 > also attached first crack at the patch to powerd.8. Both patches are
 > against 7.0 as of late January 31, EST.

Alexandre,

please remove my gratuitous 4-line comment at the top, it's OTT and was
really just to document for myself what I was playing around with then.

Though it's implied, I think the mod to powerd(8) should mention that
tz0 is the default.  Also I think 999C is just a wee bit high to test
against, when 150C would melt most laptops (not to mention laps :)  I
recall seeing 150C tested against somewhere else as a 'reasonable' max.

Cheers, Ian

 > Johannes,
 > could you, by any chance, apply the attached patch to the original copy
 > of the powerd.c and see if it still allows you to use your system? Do
 > not expect any improvements, though ;)
 > 
 > -- 
 > Alexandre "Sunny" Kovalenko (Олександр Коваленко)
 >