kern/144232: [cpufreq] [patch] Add debug.cpufreq.highest to cpufreq

[Dan Lukes]

The following reply was made to PR kern/144232; it has been noted by GNATS.

From: Dan Lukes <dan at obluda.cz>
To: bug-followup at FreeBSD.org, spawk at acm.poly.edu
Cc:  
Subject: Re: kern/144232: [cpufreq] [patch] Add debug.cpufreq.highest to cpufreq
Date: Thu, 25 Mar 2010 11:04:15 +0100

 It sound like improper place for implementation of such logic.
 
 Cpufreq is hardware driver - it allow others to control CPU speeds. It 
 do no own decisions nor should do (imho). When it should not do 
 decisions, then it's not appropriate place to store variables that exist 
 for the purpose of such decision process only.
 
 cpufreq consumers (like powerd or acpi_thermal) are there for decision 
 making so such logic and configuration variables should be there.
 
 The debug.cpufreq.lowest is here because some reported levels are not 
 usable in the real, not because someone decided he don't want to use it.
 
 You may be interested that requested feature is implemented as part of 
 acpi_thermal. From man acpi_thermal:
 
 hw.acpi.thermal.tz%d.passive_cooling
      If set to 1, passive cooling is enabled.  It does cooling without
      fans using cpufreq(4) as the mechanism for controlling CPU speed.
      Default is enabled for tz0 where it is available.
 
 It require support from ACPI on your notebook which may or may not be 
 present. If such support is not present, so acpi_thermal can't help you, 
 then another "frequency decision" utility - e.g. - powerd - is 
 candidate-place to implement requested logic. No logic should belong to 
 cpufreq device driver itself, so no tunables for them there.
 
 I noticed the argument "maximum on AC is another than maximum on 
 battery", but power state is available to powerd, so the logic we are 
 speaking about can count the power state as well. The only question is - 
 how to tell to powerd what we want from it exactly.
 
 						Dan