[ale] Why APIC?

[Greg Freemyer]

What is the advantage of APIC that it is typically enabled by default?

I do a lot of disk i/o intensive work, and I had assumed that using
the APIC was a good thing for performance, but now I think I'm wrong.

===> Why I ask

I have a machine based on an Intel P4 MB.

I have used it regularly with SUSE 9.2 for at least a month.

Yesterday it started complaining in /var/log/warn "Kernel: APIC error
on CPU0: 60(60)"

Also the machine became unreliable and locked up a couple of times
(ie. unresponsive to the keyboard.)

Based on a quick google search, one thing to try was "noapic" in the grub entry.

I've done that, and much to my surprise the disk i/o is even faster than before.

i.e. I just did a md5sum --check and per iostat I was reading 70,000
512-byte blocks per second on 2 ide channels simultaneously.

I don't remember ever getting more than 50,000 or so before.

Even better, when one of the md5sum --check commands finished, the
other accelerated to 100,000 blocks per second.

Thanks
Greg
-- 
Greg Freemyer