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Need to understand TCB CPU and SRB CPU

 
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gandikk

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PostPosted: Mon Mar 20, 2017 9:32 pm    Post subject: Need to understand TCB CPU and SRB CPU
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Hi, I have merged 2 cobol pgms to read the input only once. I have tested the new program with 10 million records. In the spool I found the details - CPU: 0 HR 10 MIN 38.06 SEC SRB: 0 HR 00 MIN 05.97 SEC for old pgms and CPU: 0 HR 10 MIN 50.81 SEC SRB: 0 HR 00 MIN 02.34 SEC for new pgm. The CPU got increased little bit and there is 50% reduction in the SRB time. Can you help me to understand how SRB time affects overall run time of the job and Can I consider SRB time reduction as valid savings?
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Robert Sample

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PostPosted: Mon Mar 20, 2017 10:02 pm    Post subject:
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Google is your friend. Googling tcb srb returns about 86,400 hits and many on the first page of results explain the differences. For your second question, yes SRB time reduction is valid savings. HOWEVER, your program went from 644.03 seconds of CPU time (TCB + SRB) to 653.15 seconds of CPU time (TCB + SRB) -- so your "savings" is actually an increase of 1.4% (roughly) in CPU time overall.

Quote:
Can you help me to understand how SRB time affects overall run time of the job
Run time of jobs on z/OS systems is little impacted by SRB time (and, for that matter, TCB time). More important to run time are things like:
- WLM policy and how the job is classified
- Number of jobs executing
- Relative priority of your job against other jobs
- LPAR percentage CPU usage
- Disk and tape and channel utilization
etc

At a previous employer, a batch compile job could run in 5 minutes 90% of the time. However, when the site was doing month-end processing, the CPU utilization went to 100% and stayed there for 3 days or so -- and during that time, a compile would typically take 5 hours or more to complete. Same program, same CPU (TCB and SRB), same JCL -- the run time difference was due to the CPU running 100% with batch compiles being treated as discretionary work by WLM.
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vasanthz

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PostPosted: Mon Mar 20, 2017 11:49 pm    Post subject:
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Hi Robert,
Code:
 CPU: 0 HR 10 MIN 38.06 SEC SRB: 0 HR 00 MIN 05.97 SEC
 CPU: 0 HR 10 MIN 50.81 SEC SRB: 0 HR 00 MIN 02.34 SEC

I believe the CPU mentioned on the message is total of TCB and SRB.
IEF032I message says

Code:
CPU: xxxxx HR  xx MIN  xx.xx SEC                                         
    For processor time, which includes enclave time, preemptive class SRB
    time, client SRB time, and normalized IFA service time, xxxxx HR     
    specifies the number of hours, xx MIN specifies the number of minutes
    and xx.xx SEC specifies the number of seconds (in seconds and       
    hundredths of a second).                                             


So the calcualtion has to be
%CPU variance = ((650.81 - 638.06) / 638.06) * 100 = 1.99 = 2 percent increase in CPU compared to the old version.
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vasanthz

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PostPosted: Tue Mar 21, 2017 12:00 am    Post subject:
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Quote:
Can I consider SRB time reduction as valid savings?

You have to add the SRB and TCB time and compare the two runs, to assess if your program has performance improvement.

TCB is the time required to execute the program statements.
SRB is the time spent on system tasks on behalf of the program.
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Robert Sample

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PostPosted: Tue Mar 21, 2017 12:29 am    Post subject:
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I'm used to the user exit format for CPU timings:
Code:
                                      -----TIMINGS (MINS.)------               
STEPNAME PROCSTEP    RC   EXCP   CONN       TCB       SRB  CLOCK          SERV
         ZPARM       00   2233     31       .00       .00     .0          2705
         CONFZMF     00     85      1       .00       .00    3.2           499
         ZOSMF       00 44724K  11186    145.31      7.33 7963.8   19313169080
where the TCB and SRB times are separated. My apologies for not realizing the format of the OP's message wasn't the same.

However, the bottom line remains for the OP -- yes, SRB time went down but the overall CPU time went up. As shown above, SRB is typically much lower than TCB (although the SRB usage depends upon how the program is using system resources), but both are CPU time and are combined to get total CPU usage.
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gandikk

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PostPosted: Tue Mar 21, 2017 12:35 am    Post subject: Reply to: Need to understand TCB CPU and SRB CPU
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Thank you Robert & Vasanthz!! Your explanation helped me to understand the difference between TCB and SRB.
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Bill Woodger

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PostPosted: Tue Mar 21, 2017 2:40 am    Post subject: Reply to: Need to understand TCB CPU and SRB CPU
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You have taken two COBOL programs which read the same data, and made them into one program? For 10m records you should have noticeable savings.

Did you thoroughly test the new program before tossing a lot of records into it? There's something wrong, which either affects the logic or you've picked a bad way to do something.
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gandikk

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PostPosted: Tue Mar 21, 2017 5:01 am    Post subject: Reply to: Need to understand TCB CPU and SRB CPU
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Bill, I have tested this program with 1000 and 250K samples to compare the results. One of the tech in our team used the new pgm over the weekend to run his code for 270 million records. We have identified savings in this case.

Old Code:
CPU: 1 HR 56 MIN 38.73 SEC SRB: 0 HR 02 MIN 11.39 SEC - 1st Cobol pgm
CPU: 3 HR 25 MIN 45.14 SEC SRB: 0 HR 02 MIN 33.42 SEC - 2nd Cobol pgm

New Code:

CPU: 5 HR 15 MIN 00.85 SEC SRB: 0 HR 02 MIN 07.18 SEC
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steve-myers

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PostPosted: Tue Mar 21, 2017 5:20 am    Post subject:
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Mr. Woodger is correct about testing the new program very carefully.

The method you used to combine the two programs may have introduced overheads that would pretty much negate any TCB CPU time savings, leaving a small SRB time savings. Since there is no practical way for an ordinary program to control the amount of SRB CPU time the program uses, I would discount this "savings."

Still, it looks to me you got back 15 minutes or so. Not bad at all!
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gandikk

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PostPosted: Wed Mar 22, 2017 1:18 am    Post subject: Reply to: Need to understand TCB CPU and SRB CPU
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Vasanthz, you have mentioned that CPU is the total of TCB and SRB. But in one of my jobs, CPU is less than the SRB time.

CPU: 0 HR 03 MIN 50.88 SEC SRB: 0 HR 10 MIN 17.11 SEC

It is a sort step is pulling the records based on some criteria. Why do we have CPU less than SRB?

Thank you!!
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vasanthz

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PostPosted: Wed Mar 22, 2017 4:05 am    Post subject:
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Quote:
But in one of my jobs, CPU is less than the SRB time.

CPU: 0 HR 03 MIN 50.88 SEC SRB: 0 HR 10 MIN 17.11 SEC


Wow. I got no explanation for that. Maybe the time is actually TCB and I was wrong all along.

Let me check couple of things.
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Robert Sample

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PostPosted: Wed Mar 22, 2017 4:41 am    Post subject:
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gandikk, is there an IEF032I message identifier anywhere in your output? If not, CPU may represent TCB time -- CPU is the total for IEF032I, but not necessarily for any other message.
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