The SRM constants below are used to make zOS installation specifications (such as IEAOPTxx parameters) transparent across the IBM processor range. SRM, the system resources manager, is the component of the system control program which determines which address spaces should be given access to system resources and the rate at which each address space is allowed to consume resources. The amount of service consumed by an address space is computed by SRM according to the formula:
service = CPU service + SRB service + IO service + Storage service
where, in particular,
CPU service = CPU x CPU service units;
SRB service = SRB x SRB service units.
Here CPU and SRB are service definition coefficients specified in the IPS (installation performance specification), the IEAOPTxx member of SYS1.PARMLIB. (The values for CPU and SRB in the default IPS are 10.0.) The CPU service units are the task (TCB) execution time multiplied by the SRM constant for the processor model (as partitioned, if applicable). Similarly, the SRB service units are the service request block (SRB) execution time multiplied by the SRM constant for the processor. Thus the SRM constants table relates processor execution time with the CPU/SRB portion of service as calculated by SRM. (Calculations will need to allow for the possiblity that some of the CPU/SRB service time goes uncaptured by the reporting software.)
For further details on the SRM constants and their use see Chapter 3, Section 4 of z/OS MVS Initialization and Tuning Guide, SA22-7591.
SRM constants are used by z/OS for workload management and provide a gross level indicator of processor capacity on an average workload mix basis. However, because processor designs can be workload sensitive, where a finer estimate of relative performance is required based on specific workload characteristics, the underlying detailed Large Systems Performance Reference (LSPR) data should be used to create customized capacity ratios. These detailed LSPR ratios provide relative performance data for a comprehensive set of workloads and are available online; see Large Systems Performance Reference. Because the SRM constants and LSPR ratios may represent measurements at different points in time, it is not possible to specify a fixed relationship between ratios of SRM constants and some set of LSPR ratios.
SRM constants for IBM processors
The columns labeled STIDP TYPE and STIDP VersCode refer to the corresponding fields as returned by the STIDP (Store CPU ID) instruction and recorded in the RMF CPU Activity Report.
NOTE: zSeries 900 models are not assigned Version Codes.
SRM constants are explicitly listed for certain partitioned processors. For partitioned processors which are not listed, use the SRM constant for the immediately preceding processor with the same number of CPs as the partition. (The version code remains the version code from the unpartitioned processor.) For example, for a 4-way partion of a 9672-RY5 the version code is 7B and the SRM constant is SU/SEC = 2902.7576 (explicit), while for a 4-way partition of a 9672-RX5 the version code is 7A and the SRM constant is SU/SEC = 2597.4026 (implicitly derived from the 4-way partition of the 9672-R55). Similarly, a 5-way partition of the 9672-RX5 would have a version code of 7A and an SRM constant of SU/SEC = 2472.1879 (implicitly derived from the unpartitioned 9672-R55).