Intel 170 Servers User Manual
and higher than normal CFINT values. The goal is to avoid exceeding the threshold (knee of the curve)
value of interactive capacity.
value of interactive capacity.
2.8 Interactive Utilization
When the interactive CPW utilization is beyond the knee of the curve, the following formulas can be used
to determine the effective interactive utilization or the available/remaining client/server CPW. These
equations apply to all server models.
to determine the effective interactive utilization or the available/remaining client/server CPW. These
equations apply to all server models.
CPWcs(maximum) = client/server CPW maximum value
CPWint(maximum) = interactive CPW maximum value
CPWint(knee) = interactive CPW at the knee of the curve
CPWint = interactive CPW of the workload
CPWint(maximum) = interactive CPW maximum value
CPWint(knee) = interactive CPW at the knee of the curve
CPWint = interactive CPW of the workload
X is the ratio that says how far into the overhead zone the workload has extended:
X = (CPWint - CPWint(knee)) / (CPWint(maximum) - CPWint(knee))
X = (CPWint - CPWint(knee)) / (CPWint(maximum) - CPWint(knee))
EIU = Effective interactive utilization. In other words, the free running, CPWint(knee), interactive plus the
combination of interactive and overhead generated by X.
EIU = CPWint(knee) + (X * (CPWcs(maximum) - CPWint(knee)))
combination of interactive and overhead generated by X.
EIU = CPWint(knee) + (X * (CPWcs(maximum) - CPWint(knee)))
CPW remaining for batch = CPWcs(maximum) - EIU
Example 1:
A model 7xx server has a Processor CPW of 240 and an Interactive CPW of 70.
The interactive CPU percent at the knee equals (70 CPW / 240 CPW) or 29.2%.
The maximum interactive CPU percent (7/6 of the Interactive CPW ) equals (81.7 CPW / 240 CPW) or
34%.
The interactive CPU percent at the knee equals (70 CPW / 240 CPW) or 29.2%.
The maximum interactive CPU percent (7/6 of the Interactive CPW ) equals (81.7 CPW / 240 CPW) or
34%.
Now if the interactive CPU is held to less than 29.2% CPU (the knee), then the CPU available for the
System, Batch, and Client/Server work is 100% - the Interactive CPU used.
System, Batch, and Client/Server work is 100% - the Interactive CPU used.
If the interactive CPU is allowed to grow above the knee, say for example 32.1 % (110% of the knee),
then the CPU percent remaining for the Batch and System is calculated using the formulas above:
then the CPU percent remaining for the Batch and System is calculated using the formulas above:
X = (32.1 - 29.2) / (34 - 29.2) = .604
EIU = 29.2 + (.604 * (100 - 29.2)) = 71.9%
EIU = 29.2 + (.604 * (100 - 29.2)) = 71.9%
CPW remaining for batch = 100 - 71.9 = 28.1%
Note that a swing of + or - 1% interactive CPU yields a swing of effective interactive utilization (EIU)
from 57% to 87%. Also note that on custom servers and 7xx models, environments that go beyond the
interactive knee may experience erratic behavior.
from 57% to 87%. Also note that on custom servers and 7xx models, environments that go beyond the
interactive knee may experience erratic behavior.
Example 2:
A Server Model has a Client/Server CPW of 450 and an Interactive CPW of 50.
The maximum interactive CPU percent equals (50 CPW / 450 CPW) or 11%.
The interactive CPU percent at the knee is 1/3 the maximum interactive value. This would equal 4%.
The maximum interactive CPU percent equals (50 CPW / 450 CPW) or 11%.
The interactive CPU percent at the knee is 1/3 the maximum interactive value. This would equal 4%.
IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
©
Copyright IBM Corp. 2008
Chapter 2 - Server Performance Behavior
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