If PCS (Performance Control Subsystem) is running under VM2000, the CPU quota of the corresponding guest system is taken into account internally. In other words, within a guest system the sum of the S-Q MAX value for response time-critical categories should be 100 (corresponds to 100% of the guest system capacity).
Compared to native operation, a correction generally needs to be made to the parameters of the SERVICE ranges (range between SERVICE-QUOTA MIN and MAX, controlled by the dilation parameters REQUEST-DELAY MIN and MAX).
The dilation (REQUEST-DELAY) is defined as follows:
Dilation = Runtime in multiprogramming mode / Single runtime
Under VM2000, it is possible that both runtimes will increase. The single runtime can increase, for instance, as a result of increased I/O times caused by other guest systems or as a result of a reduction in hardware performance because of a lower cache hit rate.
Depending on the load profile of the individual categories in a guest system and the load profiles of the other guest systems, it is possible that the PCS dilation for individual categories may increase in comparison with native mode (which is to be expected) or decrease.
Checking or correction of the SERVICE-QUOTA and REQUEST-DELAY parameters should be done in the following sequence:
SERVICE-QUOTA MIN
This sets the service quota a category requires in normal operation, i.e. without taking workload peaks into account.SERVICE-QUOTA MAX
This sets the maximum percentage of the capacity of the guest system which can be assigned to a category during peaks in the workload.REQUEST-DELAY MIN
The system administrator should take a series of measurements to identify the value for REQUEST-DELAY ACTUAL as of which a bottleneck or unsatisfactory behavior in a category arises, i.e. the value at which the service rate should be increased. REQUEST-DELAY MIN is then set to this value.REQUEST-DELAY MAX
This defines the degree of response to a workload peak. The nearer this value is set to that of REQUEST-DELAY MIN, i.e. the smaller the value, the stronger the reaction to peaks in the workload.