157k interrupts per second causing 60% CPU load on idle system

[Gary Palmer]

On Tue, Mar 20, 2012 at 11:10:10PM +1030, Matt Thyer wrote:
> On 20 March 2012 22:24, Ivan Voras <ivoras at freebsd.org> wrote:
> 
> > On 20 March 2012 12:52, Matt Thyer <matt.thyer at gmail.com> wrote:
> > > On 20 March 2012 21:12, Ivan Voras <ivoras at freebsd.org> wrote:
> > >>
> > >> On 20/03/2012 06:26, Matt Thyer wrote:
> > >> > I've upgraded my FreeBSD-STABLE NAS from r225723 (22nd Sept 2011) to
> > >> > r232477 (4th Mar 2012) and am finding that a system process called
> > >> > "intr"
> > >> > is now constantly using about 60% of 1 CPU starting a short time after
> > >> > reboot (possibly triggered by use of the samba server).
> > >> >
> > >> > When this starts, systat -vm 1 says that the system is 85% idle and
> > 14%
> > >> > interrupt handling.
> > >> > It says that there's around 157k interrupts per second.
> > >> >
> > >>
> > >> Ok, but *which* interrupt is getting triggered? Please send the output
> > >> of "vmstat -i".
> > >>
> > >>
> > > interrupt                          total       rate
> > > irq16: uhci0+                 3392184862     126692
> >
> > Ok, something's probably wrong with USB. Can you disable it in BIOS?
> >
> >
> > > cpu0: timer                     53549677       1999
> > > irq256: mps0                     2643187         98
> > > irq257: re0                      5508108        205
> > > irq258: ahci0                     160717          6
> > > cpu1: timer                     53525300       1999
> > > cpu2: timer                     53525300       1999
> > > cpu3: timer                     53525296       1999
> > > Total                         3614622447     134999
> > >
> >
> 
> I did just update the BIOS at about the same time so the difference may be
> due to that change.
> 
> I'll try a few things such as:
> 
> - Unplugging any USB things (I've only got a keyboard plugged in).
> - Downgrade BIOS.
> 
> I'll get back to you all soon.

It would be interesting to know if there are other devices on irq16 also.

grep 'irq 16' /var/run/dmesg.boot

I think the '+' on the irq16 line from vmstat means the interrupt is
shared, but the man page doesn't mention it so I'm not 100% sure

Thanks,

Gary