Bug#275572: This is ACPI related, and fixed in 2.6.9
Version 2.6.8-4 of kernel-image-2.6.8-1-k7-smp has different symptoms:
kacpid uses 100% CPU time when a UPS is connected to the serial port.
On 2.4.22 and .27 kernels (and presumably all others with recent ACPI),
keventd uses 100% CPU time. I can run top and see kacpid/keventd jump up to
100% CPU or drop off when I connect/disconnect the RS-232 cable.
A tech support guy at my vendor told me ---------
We have seen the ACPI problem with several UPS brands/models on certain
kernels. As you mentioned newer kernels do not seem to exhibit this
problem, and another workaround is always using acpi turned off in the BIOS.
-------------------------------------------------
Disabling ACPI in the BIOS solves the problem. So does booting with
ACPI=off. I don't remember if other BIOS ACPI settings (i.e. ACPI V2, or
ACPI APIC, or inclusion of various tables) had an effect, but I don't think
so.
The problem doesn't happen with a 2.6.9 kernel I compiled myself from
vanilla kernel.org source. (This is all with i386 kernels. 64bit 2.6
kernels will oops in kacpid or will have the keyboard freeze within a few
minutes. (They unfreeze when the cable is unplugged from the UPS). I
haven't tested a 64bit 2.6.9, but I can if you want to know whether it's
worth pushing it into Sarge.)
This will mainly affect people who admin servers, since dual-Opteron Tyan
boards w/ UPSes aren't typical for home users. My point is that putting
the acpi=off info in an install FAQ is probably good enough for people who
might be affected by this when installing Sarge.
--
#define X(x,y) x##y
Peter Cordes ; e-mail: X(peter@cor , des.ca)
"The gods confound the man who first found out how to distinguish the hours!
Confound him, too, who in this place set up a sundial, to cut and hack
my day so wretchedly into small pieces!" -- Plautus, 200 BC
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