APIC and ACPI, etc

[James Wilkinson]

Brian Fahrlander wrote:
>     Since FC2 I've noticed a trend towards hardware sensitivity.  I have
> only one problem with APIC; and that's that it's so close to ACPI that I
> sometimes think one and type the other.  :)
> 
>     ACPI, for those that haven't needed to deal with it, appears to be a
> radical re-think on APM, the power management daemon.  I'm guessing it's
> recent swell in development comes not only due to the 2.6 kernel, but
> the rising numbers of laptop folks who really need to know how much
> battery time they have before they have to find a power socket.
> 
>     No longer having a 'herd' of various computers to maintain, I only
> have a small glimpse into the various outcomes.  But those few that I
> have, have showed me that determining the 'kind' of acpi on the
> motherboard isn't yet perfect (Welcome to WinTel) and sometimes it's
> just a better idea for a desktop to shut it off at the kernel
> commandline with "noacpi".  But I'd be willing to bet that modern
> machines do this a lot better, now.  
> 
>     Anyone spend a lot of time in hardware? Is this the overall case, or
> just the samples I have to work with?  Is there any reason (beyond
> telling the monitor to sleep) I'd even want it for desktop use?

That looks, to me, to be a *very* good summary. It's also been rather
controversial: support for ACPI involves a large kernel-space
interpreter running vendor-provided closed-source programs with elevated
rights. Alan Cox described the ACPI spec as "bloated, complex, and very
hard to follow - and its [sic] written in my native language. I really
do not envy a random BIOS writers [sic] task."

Personally, I'm on SMP. APM doesn't work on SMP, whereas ACPI does. So
I "need" ACPI if I want my computer to be able to do a software-
controlled power down.

Unfortunately, some laptops and some of the recent Intel server hardware
(Itanium in particular) is supposed to need ACPI to be able to even
boot. And power management is coming to the desktop.

Look here for an old but good summary (scroll down a bit):
http://lwn.net/2001/0704/kernel.php3

James.

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