Task waiting for CPU, but CPU not 100% busy

Technote (FAQ)


Question

Why does a task show 'Waiting for CPU' when the CPU is not 100% busy during the time the task is running?

Cause

The CPU wait time is based on an accumulation of logical processor wait time and interval time to get the utilization time.

Answer

Tasks may show 'Waiting for CPU' time because several units of work might come in at the same time, but later there are no units of work to be done.


For example, consider a case where you have 1 logical processor and 5 units of work become ready at the same time. Four units will get CP delay while the one with the highest dispatching priority will get the processor. Then a short time later, suppose all these units of work have finished and if there are no ready units of work, the logical CP will enter a wait. If this continues over an interval you will find the CP well less than 100% busy but you will have significant CP waits reported.


Cross reference information
Segment Product Component Platform Version Edition
Systems and Asset Management Tivoli OMEGAMON II for MVS z/OS All Versions

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Document information


More support for:

Tivoli OMEGAMON XE on z/OS

Software version:

4.2, 5.1.0

Operating system(s):

z/OS

Reference #:

1431548

Modified date:

2013-05-07

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