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Old 05-26-2009, 01:00 AM   #1
nitinarora
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How to measure system jitter


Hi,

I have to measure system jitter under heady load conditions.
Can somebody tell me any open source available for the same.
If I wish to make my own program then How should I take the time stamps so that I get the most accurate reading.

gettimeofday I guess will not give the correct jitter value because it will have its own jitter introduced.
What I mean is the following code will not give the correct jitter value.

====================================================================
gettimeofday (start)
usleep(10000) // 10 ms
gettimeofday (end)
====================================================================


(end... - start....) will have gettimeofday delay as well

The correct value of jitter has to be something like this:
====================================================================
usleep() //10ms
<timestamp X: When process went to sleep for 10 ms>
.......
<timestamp Y: When process rescheduled after (10+t) ms where t is jitter>
====================================================================


Can some body tell me how to make a program which can take these timestamps.
If someone can provide me some open source for the same then it would be even better.

Thanks in Advance

Last edited by nitinarora; 05-26-2009 at 01:02 AM.
 
Old 05-26-2009, 02:15 AM   #2
syg00
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I hope you mean latency - have a look if latencytop does what you need.
 
Old 05-26-2009, 04:05 PM   #3
Quakeboy02
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A google search of "linux jiffies jitter" gave this among the other responses:
http://rds.yahoo.com/_ylt=A0geu6zsWB.../LDD3/ch07.pdf

Since this is the kernel forum, there was also at least one link to kernel code which does a jitter correction. I'll leave it to you to find that.
 
  


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