swi4: clock taking 40% cpu?!?

[Jeremy Chadwick]

On Thu, Dec 15, 2011 at 12:51:28PM -0800, Doug Barton wrote:
> Howdy,
> 
> Web server under heavy'ish load (7 on a 2 cpu system) running
> 8.2-RELEASE-p4 i386 I'm seeing this:
> 
> PID USERNAME PRI NICE   SIZE    RES STATE   C   TIME   WCPU COMMAND
> 12  root     -32    -     0K   112K WAIT    0 129:01 39.99% {swi4: clock}
> 
> Any ideas why the clock should be taking so much cpu? HZ=100 if that
> makes a difference ...

Could be wrong, but I believe this correlates with IRQ 4.  What does
vmstat -i show for a total and rate for irq4 if you run it, wait a
few seconds, then run it again?  Does the number greatly/rapidly
increase?

Shot in the dark here, but the only thing I can think of that might
cause this is software being extremely aggressive with calls to things
like gettimeofday(2) or clock_gettime(2).  Really not sure.  ntpd maybe
(unlikely but possible)?  Sort of grasping at straws here.

-- 
| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                   Mountain View, CA, US |
| Making life hard for others since 1977.               PGP 4BD6C0CB |