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CPU TIME to REAL TIME (Clock Time)

 
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gylbharat

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Joined: 31 Jul 2009
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PostPosted: Tue Jan 17, 2012 1:58 pm    Post subject: CPU TIME to REAL TIME (Clock Time)
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Hi,

I wanted to know how can we convert "TOT CPU TIME" in a JCL execution log to Real time.

Example - JCL log shows

Code:

TOT CPU TIME=  1.89 TOT ELAPSED TIME= 19.12


So How much TOT CPU TIME 1.89 = ? (Actual clock time)
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enrico-sorichetti

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PostPosted: Tue Jan 17, 2012 2:22 pm    Post subject: Reply to: CPU TIME to REAL TIME (Clock Time)
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the CPU time is the time that the CPU was busy executing Your <program> instructions
it is completely unrelated to the REAL (clock) time

ELAPSED TIME = CPU TIME + WAIT TIME (*)

nothing more, nothing less

(*) true only for strictly single thread/task processes
zOS will anyway under the covers carry on some multitasking
so sometimes the elapsed might be less than the <sum>
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gylbharat

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PostPosted: Tue Jan 17, 2012 2:49 pm    Post subject:
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Thanks Enrico...

I want to know... That in this case Example CPU TIME = 1.89, which means 1 Minute and 89 seconds. (This is on scale of 100)

But actually seconds should be <= 59.

So how can we convert 1.89 to clock time.
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Bill Woodger

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PostPosted: Tue Jan 17, 2012 3:09 pm    Post subject: Reply to: CPU TIME to REAL TIME (Clock Time)
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1.89 * 60 = number of seconds

divide number of seconds by 60, which gives minutes, and the remainder is the number of seconds that have not reached to the next minute.

Another way to look at it is 0.89 * 60. Result from any of these will always be < 60.

I may be misunderstanding something about what you are asking.
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Garry Carroll

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Joined: 08 May 2006
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Location: Dublin, Ireland / Edinburgh, Scotland

PostPosted: Tue Jan 17, 2012 3:13 pm    Post subject:
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gylbharat wrote:
Thanks Enrico...

I want to know... That in this case Example CPU TIME = 1.89, which means 1 Minute and 89 seconds. (This is on scale of 100)

But actually seconds should be <= 59.

So how can we convert 1.89 to clock time.


It doesn't mean 89sec, it means 0.89 of a minute or (60s * 0.89) = 53.4 sec

Garry.
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gylbharat

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PostPosted: Tue Jan 17, 2012 3:17 pm    Post subject:
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Garry Carroll wrote:
gylbharat wrote:
Thanks Enrico...

I want to know... That in this case Example CPU TIME = 1.89, which means 1 Minute and 89 seconds. (This is on scale of 100)

But actually seconds should be <= 59.

So how can we convert 1.89 to clock time.


It doesn't mean 89sec, it means 0.89 of a minute or (60s * 0.89) = 53.4 sec

Garry.


So total CPU TIME is 1 Minute and 53.4 Sec ?

As this 1 is also on scale of 100. Dont we have to convert it to Sec?
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Bill Woodger

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PostPosted: Tue Jan 17, 2012 3:26 pm    Post subject: Reply to: CPU TIME to REAL TIME (Clock Time)
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A minute is 60 seconds. 1/100th of a minute is 0.6 seconds.

If you want the CPU time in seconds, you have to convert it.
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Garry Carroll

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PostPosted: Tue Jan 17, 2012 3:28 pm    Post subject:
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As Bill suggests - I may be misunderstanding something about what you are asking.

Where are you getting the CPU time figure? and the reference that it's on a scale of 100?

Garry.
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gylbharat

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PostPosted: Tue Jan 17, 2012 3:30 pm    Post subject:
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I am getting from the JCL output.
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gylbharat

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PostPosted: Tue Jan 17, 2012 3:34 pm    Post subject:
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Can you show me how to convert 1.89 to seconds?
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Garry Carroll

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PostPosted: Tue Jan 17, 2012 3:38 pm    Post subject:
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gylbharat wrote:
Can you show me how to convert 1.89 to seconds?


seconds = (1.89 * 60) = 113.4s

Garry.
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gylbharat

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PostPosted: Tue Jan 17, 2012 3:46 pm    Post subject:
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Thanks Garry... Was getting confused icon_smile.gif
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Anuj Dhawan

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PostPosted: Tue Jan 17, 2012 3:49 pm    Post subject:
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Half-a-minute or 0.5 minutes (note, I did not say 0.30 minutes) or 30 seconds (0.5 x 60 seconds = 30.0 seconds) -- just differnt way of saying the same thing. As they say, a rose by any other name... .
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Robert Sample

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Joined: 06 Jun 2008
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PostPosted: Tue Jan 17, 2012 9:09 pm    Post subject:
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Elapsed time is the actual amount of wall clock time the job (or step) took. This number depends upon (among other factors):
- speed of the machine
- how many address spaces (tasks) are running at the same time
- the relative priority of your job against other tasks
- how busy the CPU is
- how much channel contention there is for the channels your task uses
- how much volume contention there is for the disk volumes your task uses
- time spent performing I/O (which includes making the request, actual reading or writing the data, and waiting for the data to come back / go to the device)
- the WLM (Workload Manager) policy in use at your site

True example: at our site, a compile job is considered discretionary (that is, it runs when nothing else wants the CPU). When the machine is not busy, a typical compile job elapsed time is 2 minutes (maybe 5 for big programs). When the machine is maxed out (CPU at 100%), the very same compile job will typically run anywhere from 3 to 8 HOURS. In other words, there is NO relationship between TCB time of a task and the elapsed time required.
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