Time spent on interrupt handling

Doug Ledford (dledford@dialnet.net)
Wed, 3 Apr 1996 04:07:10 -0600 (CST)


In conversations I have had with various people, it has been mentioned
that the kernel doesn't keep track of its time spent on handling
interrupts. First of all, is this correct? Second, if so, then could
that be changed?

Here's why I ask, the following is the output of procinfo on my news server:

Linux version 1.3.57 (root@news.dialnet.net) (gcc version 2.7.0) #24 [news.dialnet.net]

Memory: Total Used Free Shared Buffers
Mem: 63568 63056 512 11976 4948
Swap: 77820 0 77820

Bootup: Thu Mar 28 12:32:55 1996 Load average: 0.58 0.87 1.09 3/38

user : 3:56:03.11 2.9% page in : 27118978 disk 1: 17261175
nice : 0:00:00.00 0.0% page out: 16146897 disk 2: 7018575
system: 5:38:22.18 4.2% swap in : 1 disk 3: 7010241
idle : 5d 5:53:12.34 92.9% swap out: 0
uptime: 5d 15:27:37.61 context : 85140405

irq 0: 48765764 timer irq 8: 0
irq 1: 4 keyboard irq 9: 0
irq 2: 0 cascade irq 10: 45863374 DEC 21040 Tulip aic7xxx
irq 3: 1 irq 11: 31116379 aic7xxx
irq 4: 43 serial irq 12: 0
irq 5: 0 irq 13: 1 math error
irq 6: 2 irq 14: 0
irq 7: 1308 irq 15: 0

In this you will notice the extrememly high number of interrupts for the
Tulip driver as well as the aic7xxx driver. I'm curious if the time
spent handling those interrupts is accounted for in the system time usage
of that same output, or if my machine really isn't as idle as it
appears. I have another machine with a several RocketPort cards in it
and I would also like to know how much time the RocketPort driver is
taking up at the interrupt level, which is tied to the timer interrupt.
This kind of information would let me know when the system was actually
starting to bog down from interrupt processing. If the current idle
times don't reflect the time in interrupts, then a person could be
falsely led to the conclusion that the CPU isn't overworked when it
really is by the interrupt load it carries.

Would it even be possible to add this kind of acocunting into the kernel?

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