Why is intr taking up so much cpu?

[Kostik Belousov]

On Sun, Jul 18, 2010 at 10:06:06PM -0700, Doug Barton wrote:
> On 07/18/10 12:41, Kostik Belousov wrote:
> > 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.
> 
> Ok, file attached.
> 
> -- 
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>   PID    TID COMM             TDNAME           KSTACK                       
>    11 100004 intr             swi1: netisr 0   mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100005 intr             swi4: clock      mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100006 intr             swi4: clock      mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100007 intr             swi3: vm                                      
>    11 100014 intr             swi6: Giant task mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100015 intr             swi6: task queue mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100020 intr             swi2: cambio     mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100021 intr             swi5: +                                       
>    11 100022 intr             irq9: acpi0      mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100023 intr             irq16:                                        
>    11 100024 intr             irq256: hdac0    mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100026 intr             irq17: wpi0      mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100027 intr             irq20: hpet0 uhc mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100032 intr             irq21: uhci1                                  
>    11 100037 intr             irq22: uhci2     mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100042 intr             irq23: uhci3                                  
>    11 100052 intr             irq14: ata0      mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100053 intr             irq15: ata1      mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100055 intr             irq1: atkbd0     mi_switch+0x200 ithread_loop+0x1da fork_exit+0xb8 fork_trampoline+0x8 
>    11 100056 intr             irq12: psm0                                   
>    11 100057 intr             swi0: uart                                    

You should correlate the backtrace and the id of the cpu-consuming thread
(100005 or 100006, or both) and do periodic procstat -k to see which
functions are referenced most often.

Might be, suggested dtrace solution is easier.
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