Sample CPExpert "rule" description
extracted from the
TSO Component User Manual


Rule TSO212:  The maximum MPL probably is too low for TSO domain


Finding:      CPExpert has determined that a potential cause of unacceptable
              response is that the maximum MPL is too low for the domain
              servicing TSO trivial transactions.


Logic flow:   The following rules cause this rule to be invoked:
                TSO001: TSO response time is unacceptable
                TSO100: TSO transactions are swapped out
                TSO200: TSO transactions are swapped out in Active State
                TSO210: The target MPL is too low for TSO domain


Discussion:   The maximum MPL establishes the upper limit of a domain's target
              MPL.  The target MPL is the maximum number of transactions that
              may be swapped in at any one time.

If the domain's maximum MPL does not allow that target MPL to rise high enough to accommodate all ready TSO transactions, newly-ready transactions must wait until either (1) the SRM allows an Exchange on Recommendation Value swap or (2) transactions in storage complete.

Exchange on Recommendation Value swapping of TSO trivial transactions is extremely detrimental to performance in systems without extended storage. The exchange swapping should be prevented by specifying an ISV value greater than the DUR value (or allowing the ISV to default to 100,000 service units). The SRM Component of CPExpert will fire a rule if the ISV for TSO Period 1 or Period 2 is too low. Following the recommendations associated with this rule will prevent Exchange on Recommendation Value swaps for TSO trivial transactions. If newly-ready transactions must wait until transactions in storage complete (because the ISV value prevents an exchange), the delay could cause unacceptable response. CPExpert computes an estimate of the maximum number of ready TSO users. This computation is the sum of the maximum number of logically-swapped ready users (SMF70LMM) plus the average number of active TSO users (SMF72ACT/SMF72INT). RULE TSO212 fires if the estimated maximum number of ready TSO users is larger than the maximum multiprogramming value specified in the CNSTR keyword for the domain serving trivial TSO transactions. Suggestion: CPExpert suggests that the maximum multiprogramming value in the CNSTR keyword for the domain serving TSO trivial transactions be increased to the value displayed with this rule. This recommendation is simply a rule-of-thumb. The recommendation may or may not improve TSO performance. Under most conditions there is little to be lost by raising the maximum MPL for TSO Period 1, and (as explained in the discussion section above) there is much to be lost by having more ready TSO users than can be accommodated by the target MPL of the domain. There are at least three circumstances under which a smaller maximum MPL might be desirable: (1) the burst rate of ready TSO users creates excessive memory demands, (2) management might decide that there should always be a limit on the amount of resources used by TSO, and (3) non-interactive users might use TSO Period 1 or Period 2. - Burst rate of ready TSO users. Situations can occur in which many TSO users come ready within a short period. For example, the release of a file on which many TSO users are enqueued might generate a burst of ready TSO transactions within a short period. This sudden arrival of many TSO transactions could be more than the real memory could handle, without causing severe performance problems. - The SRM certainly can handle memory constraints over a period of time. However, the SRM is not easily able to respond to sudden radical changes in demand. If such a "burst rate" situation occurs, a maximum MPL level might be desirable even for TSO Period 1. (Some analysts suggest that 60-100 page frames per TSO user should be used to get a general idea of the total memory requirements implicit in the maximum MPL of TSO domains. Perhaps a better approach is to assess the average size of physically swapped users. This value is computed by dividing the number of physically- swapped users into the total pages swapped out.) - Management objectives. The TSO Component of CPExpert analyzes performance assuming that TSO should be given the resources required to satisfy interactive transactions. In some installations, TSO does not have primary priority (e.g., CICS might be considered higher priority). In these installations, management might decide to limit the share of the system's resources that TSO can acquire, even for the short time that should be required to service interactive TSO transactions. In these installations, a maximum MPL might be specified for TSO Period 1 and Period 2 to deliberately limit the access to system resources provided to TSO users. - Non-interactive users execute in Period 1 or Period 2. In some installations, the IEAICSxx member of SYS1.PARMLIB does not adequately separate interactive and non-interactive TSO transactions. In these installations, non-interactive TSO users can execute work in the performance group periods and domains assigned to TSO Period 1 and Period 2. In these cases, a maximum MPL for TSO Period 1 and Period 2 might be used to constrain the number of users, and thus constrain the overall demand on system resources. Of course, a much better alternative is to separate TSO interactive and non- interactive transactions. The SRM Component of CPExpert will detect any non-TSO workloads sharing domains with TSO Period 1 or Period 2, and issue a rule advising that this sharing not be done. However, non- interactive work can be submitted under TSO. The SRM Component is unable to detect this possibility based on its analysis of the SYS1.PARMLIB members. There is no information in the RMF Monitor I reports upon which to base a firm recommendation about the maximum MPL for the domain serving TSO trivial transactions. CPExpert recommends that the information be obtained from RMF Monitor II by the following steps: - Review the RMF Monitor II Domain Activity report during periods of high TSO activity. - Examine values in the "MAX" (maximum MPL) and "MPLT" (current target MPL) columns opposite the domain serving TSO trivial transactions. - If the "MPLT" value is at (or even near) the "MAX" value, the maximum MPL level should be increased unless management wishes to restrict TSO use of system resources.

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Last updated by Don Deese on 11/10/97.