[ale] [On-topic] "wa" number in "top"?

[JK]

Hi folks,

I have an app that regularly (1/day) hangs the machine
it is running on, without leaving any useful output in
its log.  When this scenario occurs, a "top" left running
on the console reveals that at the time of the hang,
100% of the CPU time is spent in the "wa" state. But I
cannot find a definitive explanation of what the "wa"
value means. I conjecture that it is time waiting for I/O
to complete, but that would be strange, since I/O waits
shouldn't use CPU time -- they should just block the
waiting thread. (Spinlocks, perhaps? But on a single-CPU
box, so probably not.  We've disabled hyperthreading
and still get periodic hangs, but *only* when our
pet app is running.)

I've looked at the source for top, and found the meanings
for every value in the top UI *except* "wa"; apparently
Red Hat ships a modified version of top with Fedora
(the distro in question), and I haven't had time to
track that down yet. Google hasn't been particularly
helpful either.

A possibly-relevant fact is that the app in question is
making heavy use of a Rocketport multi-port serial card.
We have the source for the driver, but I haven't had
time to look at it. I also don't happen to know off
the top of my head the kernel running on the machine,
but it's almost certainly the stock FC3 one, whatever
version that is.

Any clues would be appreciated. Really, just knowing
exactly what "wa" means would be a big help.

Thanks,

-- JK