[KLUG Members] Should I boot with APIC enabled in RedHat 9 SMP?

[Bob Kanaley]

Greetings all,

I am building a dual Xeon 2.4Ghz system using a SuperMicro P4DME-M
motherboard (Intel E7500 chipset). This is going to be a mission critical
server. The app developer wants it to be as fast as possible, but I want it
as stable as possible.

When I boot with kernel 2.4.20-8smp or 2.4.20-20.9.i686smp, I get “An
unexpected IO-APIC was found” in dmesg. When I look in /proc/interrupts I
find that only one of the four virtual CPU’s are using the extended IO-APIC
interrupts.

Most of the googling I did suggested that this is an APM motherboard bios
problem, but even with APM turned off in the bios and the kernel I still get
this message. This leads me to suspect that there is an IO-APIC problem in
the E7500 chipset.

If I boot the kernel with the noapic option, there are a couple of boot
message references to APIC in dmesg, but no errors are reported. Cat
/proc/interrupts shows that the extended IO-APIC table has not been loaded,
so the extended interrupts are not being used.

Does booting with APIC extended interrupts enabled for one CPU offer any
great performance benefits over the noapic boot?

Can using the extended IO-APIC interrupts after an unexpected IO-APIC
message result in stability problems?

TIA,

Bob

Robert V. Kanaley
Manager Information Systems
Agdia, Inc.
rvk@agdia.com
http://www.agdia.com