Why is intr taking up so much cpu?

[Kostik Belousov]

On Sun, Jul 18, 2010 at 12:21:00PM -0700, Doug Barton wrote:
> On 07/18/10 03:30, Kostik Belousov wrote:
> > On Sun, Jul 18, 2010 at 01:14:41AM -0700, Doug Barton wrote:
> >> On Sat, 17 Jul 2010, Kostik Belousov wrote:
> >>
> >>> Run top in the mode where all system threads are shown separately
> >>> (e.g. top -HS seems to do it), then watch what thread eats the processor.
> >>
> >> And the winner is!
> >>
> >>    11 root       -32    -     0K   168K WAIT    0   0:28 18.02% {swi4: 
> >>    clock}
> >>    11 root    21 -64    -     0K   168K WAIT    0   1:17 18.90% intr
> >>
> >> The first is with -H, the second without.
> >
> > Most likely it is some callout handling. Just in case, do you have
> > console screensaver active ?
> 
> I assume you mean "saver=yes" in rc.conf, and the answer is no, I am not
> using that. Usually I run xscreensaver, but at the time this happened I
> was not. I do have DPMS enabled in my X config though.
> 
> Any suggestions on how to dig deeper on this? Are there any settings I
> can twiddle to try and mitigate it?
When intr time starts accumulating again, try to do
"procstat -kk <intr process pid>" and correlate the clock thread tid
with the backtrace. Might be, it helps to guess what callouts are eating
the CPU.
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