Re: High interrupt CPU usage in top

[Mark Cullen <mark.r.cullen@xxxxxxxxx>]

Danial Thom wrote:
> --- Mark Cullen <mark.r.cullen@xxxxxxxxx> wrote:
>
>
> > Oliver Fromme wrote:
> >
> > > Mark Cullen <mark.r.cullen@xxxxxxxxx> wrote:
> > > > I don't know if it is anything to be
> >
> > concerned about, but I seem to be 
> >
> > > > seeing high interrupt CPU usage in top (at
> >
> > least) when compiling things...
> >
> > > > 
> > > > ---
> > > > load averages:  0.81,  0.57,  0.36        
> >
> >             up 0+00:37:49 
> >
> > > > 15:41:44
> > > > 43 processes:  2 running, 41 sleeping
> > > > CPU states: 37.1% user,  0.0% nice, 27.9%
> >
> > system, 35.0% interrupt,  0.0% idle
> >
> > > Have you tried "vmstat -i"?  It might give an
> >
> > indication
> >
> > > if any of the device interrupts is causing
> >
> > the problem.
> >
> > > I remember a similar problem on FreeBSD
> >
> > machines where the
> >
> > > USB interrupt was shared with the NIC
> >
> > interrupt.  The USB
> >
> > > interrupt handler is quite heavy-weight, so
> >
> > it slowed down
> >
> > > the processing of NIC interrupts, even if no
> >
> > actual USB
> >
> > > devices were in use at all.  Moving the USB
> >
> > controller to
> >
> > > a different interrupt (or disabling USB
> >
> > completely) solved
> >
> > > the problem.
> > >
> > > Best regards
> > >   Oliver
> >
> > Yep, doesn't look particularly unusual to me
> > (taken while compiling 
> > multiple things)?
> >
> > interrupt                   total       rate
> > clk                       3134621        281
> > atkbd0                       5405          0
> > sio1                            0          0
> > sio0                            0          0
> > fxp0                       176854         15
> > ppc0                            1          0
> > acpi0                           0          0
> > uhci0/fxp1                      0          0
> > psm0                            0          0
> > ata0                           40          0
> > ata1                       250336         22
> > irq19                          51          0
> > swi_siopoll                     0          0
> > swi_crypto/swi_camnet           0          0
> > swi_cambio                      0          0
> > swi_vm                          0          0
> > swi_taskq                       0          0
> > Total                     3567308        319
> >
> > Looks like USB is sharing with fxp1? Not that
> > fxp1 is actually even 
> > plugged in or being used at all at the moment!!
> > Unfortuantly disabling 
> > USB is not an option for me, I have a USB ->
> > Serial converter which I 
> > need for the UPS.
>
> You'd have to do a delta as these are from system
> startup:
>
> Run "systat -vmstat 1" while compiling to see it
> real-time to see where the fat is.
>
> DT
>
>
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That's quite tricky to catch for an email, but here's my attempt.

Taken when the interrupt in top was at 22%, building world:

320 total
279 clk
    atkbd0
37  fxp0
    ata0
4   ata1
    irq19


Taken when the interrupt in top was at 5%, still building world:

288 total
281 clk
    atkbd0
7   fxp0
    ata0
    ata1
    irq19

Watching it in real-time there are some spikes where either fxp0 or ata1 
will go up to about ~40-60, but it doesn't really seem to relate to the 
number seen in top if you ask me...