rtc and smp

[Rich Payne <rdp talisman alphalinux org>]

I've been working with 2.2.13pre14 on an SMP machine and came across
something rather strange. If I compile the kernel with Enhanced Real Time
clock support (config_rtc) then it 'seems' like nothing ever gets
scheduled on the 2nd cpu. I say 'seems' because I'm looking at tools like
top (which never shows >50% cpu util) and gtop (which never shows work on
the 2nd cpu). Howver both CPUs are detected at boot and /proc/cpuinfo
reports 

'CPUs probed 2 active 2 map 0x3 IPIs 40131'

/proc/interupts shows +rtc interupts for the 2nd CPU

Now if I disable the RTC then everything looks fine.


So, is this a kernel problem or are the userland tools failing? The only
other way I could thing of testing this would be to run some sort of
benchmark, get the time it took to run, then run it twice (both at the
same time that is) and see if the second time is 2x the original (or greater).
That should in theory tell me if the 2nd CPU is being used.

Anybody have any ideas on this? It's seems a little strange, especaially
when config_rtc says 

"If you run Linux on a multiprocessor machine and said Y to
"Symmetric Multi Processing" above, you should say Y here to read
and set the RTC clock in an SMP compatible fashion."

--rdp

Rich Payne
rpayne@alphalinux.org			www.alphalinux.org