lapic: What is it? What does it do?

cwwilson721 · 03-07-2006, 02:46 AM

In dmesg, I was seeing this:

Code:

Local APIC disabled by BIOS
Enable by running lapic

I added the following to lilo.conf

Code:

append="lapic"

and now dmesg has:

Code:

Local APIC disabled by BIOS -- reenabling.
Found and enabled local APIC!
mapped APIC to ffffd000 (fee00000)

What does it do? What else is allowed with lapic working?
Thanks in advance

cathectic · 03-07-2006, 06:16 AM

http://osdev.berlios.de/pic.html

You don't actually need it enabled under Linux - its known to cause a lot of problems (e.g. on my laptop, apic is enabled by default and breaks suspend/ resume).

lestoil · 03-07-2006, 02:02 PM

apic and lapic have to do with irq asignment/control. Irq conflicts can cause crashes/freezes so no lapic or no apic are often sggested for linux installs. ACPI can handle irqs too. The /usr/src/linux/kernel-version/Documentation includes boot parameter section that may be useful. Cheers.

cwwilson721 · 03-08-2006, 12:38 PM

Don't have to worry about that....It's a laptop, so no real issues w/IRQ's...

The docs never seem to explain what apic is, just that its there.

Google pretty much does the same.

Thanks for the replies. I'll just leave it enabled until weirdness sets in.

lestoil · 03-08-2006, 12:58 PM

CW if you're iterested there is an articlle by Ariel Glenn called
"Linux ACPI-Howto, The Sequel" that covers acpi vs apm and explains powermgt and various kernel parameters. It is current and extensive. Enjoy.
I agree that sometimes finding clear explanations can be a trial when data is scattered here and there. I am sure a pc tech's linux/windows troubleshooting handbook will cover apic and lapic beyond just saying if you have this occur then pass this parameter.

cwwilson721 · 03-08-2006, 10:06 PM

Found and am reading it:

http://www.columbia.edu/~ariel/acpi/acpi_howto.html

Thanks