Date: Thu, 12 Jan 2006 14:23:27 +0100 From: Ivan Voras <ivoras@fer.hr> To: Mike Jakubik <mikej@rogers.com> Cc: stable@freebsd.org Subject: Re: powerd effectiveness Message-ID: <43C6584F.10001@fer.hr> In-Reply-To: <43C5A261.1020407@rogers.com> References: <43C5A261.1020407@rogers.com>
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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).
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