Application Management

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I wondered why IBM didn't let the native code called from the JNI run on the zAAP as well. I think that would boost the use of WAS for z/OS and push Java on z/OS. Maybe IBM thinks it would lose it licensing fees.

Exploiting zAAP
Before you decide to use zAAP, you should figure out if you'd really gain anything from it. zAAP has a fixed price of $125,000. The horsepower it provides doesn't incur software charges.

The first thing to figure out is how much of your workload is zAAP-eligible.

Currently the following z/OS subsystems might have zAAP-eligible workloads:

• WAS for z/OS 5.1
• IMS V7, V8 and V9
• CICS 2.3
• DB2 V7, V8

If you're using WAS 5.1 for z/OS, it's definitely worth exploring zAAP. For the other subsystems, you might not have a Java workload. If you need more information, refer to the product documentation.

A measurement tool, the zAAP Projection Tool for Java 2 Technology Edition, helps estimate the zAAP-eligible content in your workload. It's included in IBM JDK 1.3.1 at the PTF level UQ94379 (S2.4) or later and IBM JDK 1.4 with the PTF (or later) for APAR PQ86689.

The Projection Tool prints out the information on processor time as messages in the STDERR file for each JVM every five minutes, along with statistics and total values at termination. The report consists of:

• Java IFA time - the time accumulated for Java threads processing zAAP-eligible work;
• Java Standard CPU time - the time accumulated for Java threads processing zAAP non-eligible work;
• Interval address space CPU time - the time for working in the address space across all dispatchable units including the Java threads.

Listing 1: Project Tool output

IFA Projection data for system id=<SYSE.341> Starting at:
16:25:07 - Current address space CPU: 0.025418 sec.
<SYSE.341> Interval at: 16:28:15 Switches To/From IFA: 17
Java IFA: 0.411787 sec. Java Standard CPU 0.000059 sec.
Total address space CPU: 3.266723 sec.
<SYSE.341> Interval at: 16:28:40 Switches To/From IFA: 77
Java IFA: 3.421488 sec. Java Standard CPU 0.008685 sec.
Total address space CPU: 0.583209 sec.
<SYSE.341> TOTAL at: 16:28:40 Switches To/From IFA: 94
Java IFA: 3.833275 sec. Java Standard CPU 0.008744 sec.
Total address space CPU: 3.849932 sec.

Listing 1 is the STDERR file containing the project tool output.

To analyze this data further, an Excel workbook is provided at www6.software.ibm.com/dl/zosjava2/zosjava2-p. It processes the STDERR file and stores the zAAP processing information in a spreadsheet. Figure 4 is a sample of the contents of the spreadsheet after executing in the workbook. This Figure is from IBM's technical document.

The workbook combines data from multiple JVMs and multiple address spaces, service classes, and LPARs, aligns data to RMF intervals, adjusts zAAP utilization factoring in the z/OA capture ratios, and expresses zAAP and standard CP time as a percent of the single CP that the data was collected on.

Based on the information provided by the Projection Tool, you can work with your zSeries capacity planning staff to determine how much you can gain from using zAAP and how many zAAPs you should use. I don't want to get into too much detail on this because it involves a lot of factors regarding zSeries capacity planning. Normally Java developers have no interest in it.

Using the Projection Tool with WAS for z/OS is quite straightforward. The following steps apply to different versions of WAS for z/OS:

• Step1: Upgrade the JVM to the service level that supports the Projection Tool.
• Step2: Change the JVM option and application server configuration to enable the JVM to produce the processor time information.
• Step3: Test that your application can capture the information.
• Step4: Disable the Projection Tool.
• Step5: Analyze the data captured using the Excel workbook.

Should you need more information on how to do it, refer to www-03.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/WP100431

Using zAAP
This section describes setting the JVM options for leveraging zAAP, measuring zAAP utilization, and some zAAP-related performance topics.

IBM JDK1.4.1 has a set of options for zAAP processing. If you are on z/OS V1R6, the default values of the JVM options enable you to use zAAP automatically. These are the JVM options:

• Xifa:on - This is the default option on JDK 1.4.1. It enables a Java workload to run on a zAAP if available. It's only honored on z/OS V1R6.
• Xifa:off - This option disables the zAAPs.
• Xifa:projectn - This option is provided so the Project Tool can gather processor time information to help zAAP capacity planning. "n" is the requested time interval to print out the processor time information. A value of "0" indicates that the information will only be written when Java terminates. Messages are normally written after a switch has been encountered for zAAP-eligible work or when returning from that state. This option can be used on all z/OS versions for capacity planning purpose. On z/OS V1R6, SMF and RMF reports have the zAAP capacity planning information. This option disables zAAP use on z/OS V1R6 unless you specify Xifa:on or Xifa:force.
• Xifa:force - This option forces Java to continue trying to use zAAPs even if none exist. This option is only honored on z/OS V1R6 to collect RMF/SMF data to assess potential zAAP use.

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