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XENTIS CPU Utilization and System Quantum

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Abstract

The impact of XENTIS on your system can be lessened by adjusting the QUANTUM parameter downward. By reducing the amount of time in a time slice, the few processes that tend to use the full time slice, like XENTIS, will appear to use less system resources, while other processes that normally do not use the full time slice will not be impacted. QUANTUM is a dynamic parameter; in order for a change to take affect, the system does not have to be rebooted.

Discussion

If it appears that XENTIS is getting more than its fair share of thesystem resources, this is because VMS gives it more, not because XENTIS requests more. XENTIS does not request additional resources from the operating system, nor does it raise its priority (unless you specify a higher priority in the Setup File and you install XENTIS with ALTPRI privilege).

Some background information is necessary to properly explain the situation.VMS systems that use XENTIS as their report writer are typically used for commercial applications. Examples of commercial applications include accounting, distribution, manufacturing, etc. Traditionally, these types of applications exhibit a data processing bottleneck with disk I/O. XENTIS was designed with a solution to this performance problem in mind. As a result, XENTIS was programmed to reduce disk I/O and paging as much as possible.

On a single CPU system, only one process can run at a time. All processes on the system are either in a run state or a wait state. A process is in run state when executing in the CPU. A process is in wait state when waiting for terminal or disk I/O, for paging to occur, to run because another process is currently running, or for some other resource that is not available.Once in run state, a process continues until it uses up its allotted time slice, known as QUANTUM on a VMS system, or until it goes into a wait state at which time it gives up the remaining time slice.

XENTIS was programmed to avoid going into a wait state (usually caused by disk I/O). Unlike most processes on the system, XENTIS tends to use up its full time slice before going into a wait state. When it does go into wait state, it immediately gets in line to run again. The result is that XENTIS appears to use more system resources than other processes.

The SYSGEN parameter QUANTUM controls the amount of time in a time slice (how long a process can use the CPU before being forced to give it up).