acpi(4) corrections, clarifications

[b. f.]

While this documentation cleanup is going on, I'd like to point out
that acpi(4) could use some improvements:

(1)In the "SYSCTL VARIABLES" section, under hw.acpi.cpu.cx_lowest,
acpi(4) states "To enable ACPI CPU idling control,
machdep.cpu_idle_hlt must be set to 1".  However, apparently only the
pc98 port still uses this OID, while amd64, i386, etc., use something
like machdep.idle=hlt, so this remark should be changed.  And in any
case, is this statement correct?  Can't idling now be used with other
values of machdep.idle, like mwait, mwait_hlt, amdc1e, hlt, and acpi?

(2)Under the "BUGS" section, acpi(4) states:

"The acpi CPU idle power management drive conflicts with the local
APIC (LAPIC) timer. Disable APIC mode with hint.apic.0.disabled or do
not use the C2 and C3 states if APIC mode is enabled."

However, mav@, in his recent series of recommendations on
power-saving, advocated the use of hints like hint.apic.0.clock="0"
instead.  Is simply turning off the timer sufficient to use the deeper
sleep states, or must all of the local apic be disabled?  Some
machines won't boot with hint.apic.0.disabled, so it would be useful
to determine whether this is really necessary.


Regards,
                b.