Do desktop users need ACPI?

Joseph K. · Posted: Sun Dec 23, 2007 4:59 am Post subject: Do desktop users need ACPI?

My short question is: can I safely remove ACPI from the kernel (under Power Management) and USE=-acpi?

My main concern is that in the kernel configuration, there is a big warning about disabling Thermal Zones for your processor. Well, I've had it enabled probably for ever, but then today realised that I never added the acpid script to the default runlevel anyway.

The only power-saving feature I'm interested in is DPMS for the monitor, which I assume does not require ACPI.

The nvidia-drivers package has optional support for ACPI: does anyone know what features this provides?

This is mostly of academic interest to me: ACPI is posing no problem for me, I'd just rather remove it if I don't need it. Thanks, cheers.

Monkeh · Veteran Joined: 06 Aug 2005 Posts: 1656 Location: England

ACPI is much more than just power management. Any modern system pretty much requires it, many won't work at all without it. You do however, only need kernel support. Nothing else needs to care about it.

albright · Posted: Sun Dec 23, 2007 2:13 pm Post subject:

In particular, acpi assigns interrupts ... I know because when I
got too smart and thought I'd just get rid of it, my sata drives
caused an interrupt conflict that prevented booting. Acpi fixed
that right up

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i92guboj · Posted: Sun Dec 23, 2007 2:24 pm Post subject:

As people say, ACPI is more than just power management.

Things like cpu throttling, hardware monitoring (which in turn can save you some money and prevent damage due to overheat if a fan fails...). Not to speak about my preferred thing: if you don't use acpi and accidentally press the power button, all your filesystems will be trashed, which in turn may mean data loss, of even a completely trashed filesystem. With the acpi daemon running, linux will correctly turn off all the running services and umount all your filesystems, preventing data loss in the way.

Monkeh · Veteran Joined: 06 Aug 2005 Posts: 1656 Location: England

Simba7 · Posted: Sun Dec 23, 2007 4:45 pm Post subject:

i92guboj · Posted: Sun Dec 23, 2007 4:47 pm Post subject:

Cyker · Veteran Joined: 15 Jun 2006 Posts: 1746

Power button behaviour varies quite wildly and depends on BIOS configuration if ACPI is not being used...

bunder · Bodhisattva Joined: 10 Apr 2004 Posts: 5947

another thing acpi is good for is turning off / rebooting your pc... if you don't have acpi, the kernel will tell you to manually power off.

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Joseph K. · Posted: Thu Dec 27, 2007 6:47 am Post subject:

I assume there is some confusion between ACPI and APIC going on here.

I have disabled ACPI and everything works fine, including hardware monitoring and fan control (controlled by the I2C bus). The only convenience that I've lost is that, as bunder mentioned, I have to power-off manually (it still reboots from software). So whilst I think you'd be mad to disable ACPI on a laptop, I'm not convinced that it offers desktop users anything really useful.

Monkeh · Veteran Joined: 06 Aug 2005 Posts: 1656 Location: England

Joseph K. · Posted: Fri Dec 28, 2007 1:49 am Post subject:

Cyker · Veteran Joined: 15 Jun 2006 Posts: 1746

Well, in theory, ACPI things you loose *can* include: lm_sensors, powernow (Speedstep too?) and lots of other powersaving stuff (Some can still be accessed via APM, but it seems a lot of mobos don't support APM now?), APIC support, HPET support, SMP support (If the mobo doesn't support MPS).

Emphasis on the *can* and *in theory*.

Lots of mobos still work with lm_sensors, even without ACPI, although some sensors may go missing or be found in different places.
SMP requires an advanced interrupt handler, so if APIC doesn't work and MPS fallback isn't working then there's the possibility multi-core/socket CPUs systems will only find one CPU.
The main loss is powersaving stuff really, 'tho much of that can still be done via APM, assuming mobo support exists...

Most of this isn't technically necessary for operation of the compy 'tho.

Joseph K. · Posted: Fri Dec 28, 2007 5:30 am Post subject:

Cyker · Veteran Joined: 15 Jun 2006 Posts: 1746

It's probably there for 'historical reasons' (i.e. when ACPI came out it was just a newer buggier version of APM. It's 'evolved' to be more, but has stayed in the same place.)

As for importance, it's very relative.

I still have a pre-ACPI 'board here and that works perfectly well without ACPI support

I even disabled APM too and just relied on the BIOS to spin down the HDs and fans.

But yeah, there is that sort of un-mentioned assumption floating around that you should know to turn it on without actually being told.
Sadly, there's alot of things like that in Linuxland still...