powerd effectiveness

[Ivan Voras]

Mike Jakubik wrote:
> It seems that powerd does very little in terms of reducing heat, and 
> sacrifices performance while doing so. Am i wrong to assume that 

> CPU: AMD Athlon(tm) Processor (1210.79-MHz 686-class CPU)

It is very unlikely this processor supports any kind of frequency 
modification by software. Basically there are two cases with modern 
processors:

- Very modern processors, from Pentium M class onwards, support true 
frequency modification, which can and does offer significant savings.
- Somewhat older processors, and the whole Celeron M line support only 
"CPU throttling", which is something like forcing idle cycles (like the 
"HLT" instruction) only on hardware level. I think this can be 
distinguished in FreeBSD by the second number in freq_levels being -1, 
like here:

dev.cpu.0.freq_levels: 1403/-1 1315/-1 1227/-1 1139/-1 1052/-1 964/-1 
876/-1 789/-1 701/-1 613/-1 526/-1 438/-1 350/-1 263/-1 175/-1 87/-1

(this second type of power management management support doesn't alter 
the physical frequency).

I think the infrastructure used by powerd supports both cases, but won't 
get you much savings if the CPU doesn't support the first case.

This information was gathered because I have a Celeron-based laptop and 
wanted to squeeze as much autonomy as possible - it may not be 
authoritative :)

What I would like for FreeSBD to support is turning off of devices like 
WinXP does. Not only hard drives, but it seems that WinXP can somehow 
turn off network cards, USB controllers and/or devices and similar 
peripherals when running on batteries and those are not used (it seems 
it's not like disabling them completely but something else).