Why is intr taking up so much cpu?

Bernd Walter ticso at cicely7.cicely.de
Sun Jul 18 10:19:36 UTC 2010

On Sat, Jul 17, 2010 at 10:21:28PM +0300, Kostik Belousov wrote:
> On Sat, Jul 17, 2010 at 12:10:26PM -0700, Doug Barton wrote:
> > On Sat, 17 Jul 2010, Rui Paulo wrote:
> > 
> > >This doesn't indicate any problem. I suggest you try to figure out what 
> > >interrupt is causing this by adding printfs or disabling drivers one by 
> > >one.
> > 
> > I've no idea where to even begin on something like that. Given that 
> > there are other -current users who are also having problems 
> > (particularly with the nvidia drivers) I'm wondering if some sort of 
> > systemic debugging isn't in order here?
> > 
> Note that intr time most likely come from the interrupt threads chewing
> the CPU, not from the real interrupt handlers doing something, and definitely
> not due to the high interrupt rate, as your vmstat -i output already shown.

I've noticed a few webpages to trigger lot of X11 related network traffic
just by watching them even without any seeable content change, but CPU
load on browser and especialy X process went high, but of course
symptoms might be different with different drivers - I use mga myself.
I never analysed it properly beacuse I'm using a quite old Xorg version,
but I see the increase of traffic on the domain socket.
I also noticed that recent firefox and seamonkey are doing lots of NFS
traffic, so I was forced to switch ~/.mozilla to a local disk, where
iostat still stays idle.
But my OS is also not very recent, so I also never debugged this problem.

> 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.

B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.

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