CPU TIME to REAL TIME (Clock Time)

gylbharat · Posted: Tue Jan 17, 2012 1:58 pm

Hi,

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

Example - JCL log shows

enrico-sorichetti · Posted: Tue Jan 17, 2012 2:22 pm

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>

gylbharat · Posted: Tue Jan 17, 2012 2:49 pm

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.

Bill Woodger · Posted: Tue Jan 17, 2012 3:09 pm

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.

Garry Carroll · Posted: Tue Jan 17, 2012 3:13 pm

gylbharat · Posted: Tue Jan 17, 2012 3:17 pm

Bill Woodger · Posted: Tue Jan 17, 2012 3:26 pm

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.

Garry Carroll · Posted: Tue Jan 17, 2012 3:28 pm

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.

gylbharat · Posted: Tue Jan 17, 2012 3:30 pm

I am getting from the JCL output.

gylbharat · Posted: Tue Jan 17, 2012 3:34 pm

Can you show me how to convert 1.89 to seconds?

Garry Carroll · Posted: Tue Jan 17, 2012 3:38 pm

gylbharat · Posted: Tue Jan 17, 2012 3:46 pm

Thanks Garry... Was getting confused

Anuj Dhawan · Posted: Tue Jan 17, 2012 3:49 pm

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... .

Robert Sample · Posted: Tue Jan 17, 2012 9:09 pm

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.