High interrupt CPU usage in top

[Mark Cullen]

Danial Thom wrote:
--- Mark Cullen <mark.r.cullen at xxxxxxxxx> wrote:


Oliver Fromme wrote:

Mark Cullen <mark.r.cullen at 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...