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Performance Management Guide

Managing Workload

When you have exhausted the program performance-improvement and system-tuning possibilities, and performance is still unsatisfactory at times, you have three choices:

If you adopt the first approach, some of your less stoic users will experience increasing frustration and decreasing productivity. If you choose to upgrade, you will most likely have to justify the expenditure. That person will undoubtedly want to know if you have exhausted all possibilities with the current system, which means you need to investigate the possibilities of workload management.

Workload management simply means assessing the components of the workload to determine whether they are all needed as soon as possible. Usually, there is work that can wait for a while; for example, a report that is needed first thing in the morning. That report is equally useful when run at 3 a.m. as at 4 p.m. on the preceding day. The difference is that at 3 a.m. it uses CPU cycles and other resources that would otherwise be idle. Use the at or crontab command to request a program to run at a specific time or at regular intervals.

Similarly, some programs that do have to be run during the day can be run at reduced priority. They will take longer to complete, but they will be less in competition with really time-critical processes.

A related technique is moving work from one machine to another; for example, running a compilation on the machine where the source code resides. This kind of workload balancing requires more planning and monitoring, because reducing the load on the network and increasing the CPU load on a server might result in a net loss.

Starting with AIX 4.3.3, AIX Workload Manager (WLM) is provided as an integrated part of the operating system kernel. WLM is designed to give the system administrator greater control over how the scheduler and virtual memory manager (VMM) allocate CPU and physical memory resources to processes. In AIX 5.1 and subsequent releases, disk usage can also be controlled by WLM. This can be used to prevent different classes of jobs from interfering with each other and to explicitly apply resources based on the requirements of different groups of users. For further information, see Server Consolidation on RS/6000.

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