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Re: High interrupt CPU usage in top


To: danial_thom@xxxxxxxxx
From: Mark Cullen <mark.r.cullen@xxxxxxxxx>
Date: Wed, 07 Jun 2006 18:38:18 +0100

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...



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