Tuning Performance › Performance and Tuning Commands › SYSRCT Command—Control Performance

SYSRCT Command—Control Performance

The SYSRCT command is used to set performance control parameters in the system Resource Control Table (RCT). It is used for performance control. It can be used to set processing unit trigger values and performance control parameters. The following types of performance control measure are supported:

• A priority change control measure
• A forced wait control measure

Performance is calculated in the following ways:

• Short-term—that is, between voluntary waits, for example, screen interaction. The SDELAY and SNPRTY operands are used for short-term evaluation.
• Long-term—that is, for the life of the NCL process. The LDELAY and LNPRTY operands are used for long-term evaluation.

This command has the following format:

SYSRCT GROUP=n
       PRIORITY=p
     [ LDELAY=( [ trigger ], [ initial ], [ adjustment ], [ limit ] ) ]
     [ SDELAY=( [ trigger ], [ initial ], [ adjustment ], [ limit ] ) ]
     [ LNPRTY=( [ trigger ], [ new_priority ] ) ]
     [ SNPRTY=( [ trigger ], [ new_priority ] ) ]

GROUP=n

Specifies the number of the performance group that is to have its RCT values updated.

Limits: 1 through 4

PRIORITY=p

Specifies the priority that is to be updated. Zero is the lowest priority.

Limits: 0 through 3

LDELAY=( [ trigger ], [ initial ], [ adjustment ], [ limit ] )

SDELAY=( [ trigger ], [ initial ], [ adjustment ], [ limit ] )

Specifies the values for forcing procedures to wait. The trigger value specifies the number of processing units that a procedure can consume before a wait is forced. The three parameters initial, adjustment, and limit specify times in hundredths of a second with a maximum absolute value of 200 (that is 2 seconds).

The initial value is used for setting the period of the first wait. Subsequent wait times might be longer or shorter, being incremented or decremented by the adjustment value, which can be negative or zero. Consequently, the limit can be a maximum or minimum wait time. A zero adjustment results in the limit being set to the initial value, overriding any existing or specified value. When no limit value has been set and a positive adjustment has been specified a default maximum limit of 200 is used.

LNPRTY=( [ trigger ], [ new_priority ] )

SNPRTY=( [ trigger ], [ new_priority ] )

Specifies the values for altering the priorities of procedures as they execute. The trigger value specifies a number of processing units that can be consumed before a priority change occurs. The new priority must be 0 to 3 and can be the same as the current priority.

Example: Change Priority

This example sets a long-term priority change for procedures in group 1 (BACKGROUND). Priority 1 is to be altered to priority 2 after the consumption of 100 processing units.

SYSRCT G=1 P=1 LNP=(100,2)

The SYSPGT command can have been used to set the initial priority for this performance group to be 1.

Example: Force Waits

This example sets a forced wait for procedures running in priority 2 to occur every 20 processing units. The first wait would be for an interval of 5 hundredths of a second, the second would be 6, the third 7, and so on, until the maximum of 20 hundredths (0.2 seconds) is reached.

SYSRCT GROUP=1 PRIORITY=2 SDELAY=(20,5,1,20)

Example: Change Delay

This example alters only the short term delay value limit to be 30 hundredths of a second.

SYSRCT GR=1 PR1=2 SDELAY=(,,,30)

Remarks

Processing units are a simple measure of work arbitrarily assigned to the execution of NCL statements. They are in no way an accurate measure of actual work performed, or an approximation of CPU time consumed. You cannot compare the work done by two different NCL processes based on processing units consumed.

There are two sets of processing unit consumption statistics for each NCL procedure—one for short-term evaluation and the second for long-term evaluation. It also maintains a long-term dispatching priority as well as a current dispatching priority. Short-term statistics are reset whenever a voluntary loss of control occurs or a priority change takes place. A short-term priority change alters only the current dispatching priority, whereas a long term priority change alters both priorities.

The order of evaluation of performance control measures is as follows:

1. Long-term forced wait and priority change check
2. Short-term forced wait and priority change check

Only the first of the above that is triggered is actioned; however, both a priority change and a wait can occur at the same time, with the wait being actioned before the priority change. Procedures started using an &INTCMD statement are run in the owning process’s performance group, starting at the performance group’s initial priority.

The four performance groups are BACKGROUND, OCS, FULLSCREEN, and SYSTEM, numbered 1 to 4 respectively.