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Out of order timings of gettimeofday_us()
- From: "Nathan A. Debardeleben" <ndebard at lanl dot gov>
- To: systemtap at sourceware dot org
- Date: Tue, 23 Jan 2007 15:33:48 -0700 (MST)
- Subject: Out of order timings of gettimeofday_us()
- Reply-to: ndebard at lanl dot gov
I have a very simple script which seems to demonstrate time values coming
out of gettimeofday_us() being out of order. I believe this function I am
probing is extremely fast - but, regardless, it shouldn't take negative
time to complete. :)
Here's the probe:
probe kernel.function("cbe_system_reset_exception") {
printf(" IN: %d\n", gettimeofday_us());
}
probe kernel.function("cbe_system_reset_exception").return {
printf("OUT: %d\n", gettimeofday_us());
}
Here's some output from it:
IN: 1169591399721428
OUT: 1169591399721437
IN: 1169591399721484
OUT: 1169591399721492
IN: 1169591399722383
OUT: 1169591399722298 **** ERROR - NOTICE this is before the above "IN" line
IN: 1169591399723387
OUT: 1169591399723302 **** ALSO OUT OF ORDER!
. . .
I annotated the above line where I see an error. This happens very often
with this probe.
Is the us() timing just too fine grained? If it's acting like this here I
question its values in other places.
Please advise.