IT Management

Workload Manager:  Revisiting Goals Over Time

6 Pages

SCENARIO 4: DESIRE TO EXPLOIT ADDITIONAL WLM FUNCTIONS

Your systems are running great in goal mode, but now you want to take advantage of some WLM functions that you have not yet exploited. Perhaps these are functions introduced with a new release of z/OS, or maybe they are existing functions that you just have not yet had the opportunity to try out. Will the exploitation of various WLM functions that are not already being exploited have an influence on the assigned goals or WLM Service Definition? The answer is a simple yes. Since WLM was first announced, there has been a steady stream of enhancements. Enabling or exploiting most of these new functions will change the way WLM manages the workloads and resources. Because of the power of these enhancements, the WLM design team has made most of them optional. Naturally, it follows that if you want to exploit any of these new functions, you have to change your WLM Service Definition.

I caution you that enabling any of these functions does require investigation, thought, and a before-and-after assessment of the effect any change has on goals, workloads, and WLM management. Figure 3 shows a list of WLM enhancements and the categories in which they fall. Although few are required, all deserve consideration, and all either benefit or hurt your workloads. There are other enhancements, but for brevity, I listed the ones that I find most interesting.

 

SCENARIO 5: CHANGES TO WLM, SYSTEM PROBLEMS, IMPROPER TUNING

Your performance monitors indicate that some response time goals are being missed due to high response times, and work with velocity goals is showing abnormal velocities. Some users are calling and complaining, or maybe the systems seem “sluggish.” However, your performance monitors indicate that WLM is doing the best it can! The dispatch priorities seem to be correct; there is no paging, and WLM delay samples are nearly non-existent. What is going on?

Why is it that WLM appears to be doing its best, but work is still not performing well, or goals are being missed? Are changes required to the WLM controls?

The key to this scenario is to remember that WLM may not be able to meet goals on systems that are out of capacity or for systems that are not tuned. WLM is only going to help in one aspect of workload management. You still have to tune your systems, Sysplexes, subsystems, and workloads.

No matter how well-intentioned a WLM goal is, it is only an objective for WLM to alleviate delays it knows about  using controls over which it has control. In other words, workloads could be missing their goals due to reasons beyond WLM’s control. For example, if a workload is missing its response time goal because it is spending too much time in the coupling facility, WLM is currently not capable of tuning the coupling facility or structures to help this work meet its objectives. Therefore, no matter how hard WLM tries, it may not be able to help this workload if its real problem is an improperly tuned coupling facility or structure.

6 Pages