dtrace discuss - Jan 2008 - Kernel''s microstat accounting doesn''t work in this situation, doesn''t it? (Using DTrace as the trigger)

Hi all:

I''m working on revealing system performance now.
My testing program is an infinite loop. Inside the loop, it will do some
mathematical opertaions and call function callee(), then go to the next
loop.
I install a alarm(30) in the program. It means it will stop after running 30
seconds.
Before calling alarm(30), at the beginning of the main body, it will use
libkstat to read kstat-cpu-sys record first.
After the alarm signal raised, in the signal handler, it will re-read the
kstat-cpu-sys record, and show the difference in this 30 seconds period.

For example, following is output printed on the screen,
*30.00 secs, 0.00 events per secs
user=99.7279%, kernel=0.2721%, idle=0.0000%
per second: intr=308.64, ithr=208.63, syscall=1.80, csw=78.14
per second: smtx=0.33, srw=0.00
per second: migr=0.00
*//Events are some syscalls or some user-defined functions.

In a word, this program looks very like the mpstat.

One of my testcases is running this program with dtrace''s fasttrap
provider,
such as:
dtrace -n ''pid$targer::callee:entry{ ... }'' -c my_program
dtrace -n ''test$target:::callee{ ... }'' -c my_program

The output is very strange.
*30.00 secs, 213099.33 per secs
user=99.6749%, kernel=0.3251%, idle=0.0000%
per second: intr=513.15, ithr=312.13, syscall=48.67, csw=87.27
per second: smtx=0.10, srw=0.00
per second: migr= 0.00*

In the infinite loop, callee would be called more than 2000000 times. Each
time it is called, the program would trap into kernel because it is
monitored by dtrace.

Compared with the program running with no dtrace,
*30.00 secs, 100628.74 per secs
user=99.7396%, kernel=0.2604%, idle=0.0000%
per second: intr=308.89, ithr=208.89, syscall=3.13, csw=73.24
per second: smtx=0.17, srw=0.00
per second: migr= 0.00
*
No big difference between these 2 kernel time percentages!

I think this is unbelievable! And maybe the answer is microstat accounting
system cannot log this kind of interrupt.
Since I try this program on Intel P4 platform. In i86pc, dtrace using "int
$3" to help the user program to trap into dtrace kernel module.

So, does it means that the mircostat accouting does not work in "int
$3" and
some other cases?
Am I right?

P.S. I''m using ON build 74.
Thank you.


Kind Regards,
TJ
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