© 2004 ibm corporation ibm ^ z/vm module 9: performance

© 2004 IBM Corporation

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z/VM Module 9: Performance


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Objectives

Describe what performance means in the z/VM environment List and explain the performance characteristics of the z/VM system Explain scheduling and dispatching and how they relate to

performance Describe the three lists used in scheduling and dispatching:

Dormant list Eligible list Dispatch list


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Objectives continued

Describe the planning and administration guidelines for improving z/VM system efficiency

Explain the areas of performance that need to be considered and the major factors affecting them

List and describe the CP performance facilities Describe performance guidelines in a virtual machine environment Explain the performance monitoring and analysis programs that are

available to tune your z/VM system


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Objectives continued

Describe how the INDICATE and MONITOR commands are used in performance testing

Explain why you would tune your z/VM system and the methods for doing so

List and describe the system resources that are capable of being tuned:

Processor subsystem

Paging subsystem

Storage subsystem

I/O subsystem


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Introducing Performance

Achieving optimum system performance is an elusive goal. This module will give you an understanding of z/VM system

characteristics and introduce: Performance methodology Planning measures Monitoring facility tools Tuning


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Real Processor Management

CP is responsible for allocating the processing power of the available real processors in order to process virtual machine instructions.

Any processor complex on which z/VM runs must have a master processor.

A dedicated processor runs only the work generated by that virtual machine’s processor.

To enhance the performance of the V=R machine, CP automatically dedicates as many processors as it can to the virtual processor belonging to the V=R machine.


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Real Processor Management continued

When the operator IPLs CP on the real machine, CP initially uses the master processor.

The CP in V=R machines automatically dedicates available real alternate processors under the following circumstances:

When the V=R machine defines a new virtual processor, using the DEFINE CPU command

After a VARY ONLINE PROCESSOR command, making a new real alternate processor available

When a V=R machine enters the DETACH CPU command and the detached virtual processor was dedicated


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Virtual Machine Scheduling and Dispatching

The dispatcher selects virtual machines (guests) from the dispatch list for the processors to run.

The CP scheduler function is responsible for calculating the priorities. A virtual machine is permitted to have processor control for a portion

of the elapsed time slice each time it is dispatched. An elapsed time slice is an interval of time that each virtual machine is

allocated and during which it has the use of the real processor.


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Virtual Machine Scheduling and Dispatching, continued

The scheduling and dispatching routines that are implemented in CP are designed to favor:

V=R machines

V=F machines

Interactive virtual machines over non-interactive virtual machines

Installation-specified virtual machines


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Elapsed Time Slice

When a virtual machine enters the eligible list, it is assigned an elapsed time slice.

The initial value of E1 elapsed time slice is 1.2 seconds.

The E0, E2, and E3 elapsed time slices are fixed multiples of the varying E1 elapsed time slice.


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Scheduling and Dispatching Lists

In order to schedule and dispatch the set of virtual machines, CP groups virtual machines according to their current execution characteristics and resource requirements into these groups:

Dormant list

Eligible list

Dispatch list


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Leaving and Entering the Dispatched List

Virtual machines alternate between the dispatch list and the eligible time slice.

When dropped from the dispatch list at the end of its elapsed time slice without completing its transaction, an E1 virtual machine becomes an E2 virtual machine.

A virtual machine is dropped from the dispatch list and placed in the dormant list if it enters an enable wait state (becomes idle) before its elapsed time slice ends.


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Virtual Machine Scheduling Flow


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Four Transaction Classes: Eligible List


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Dispatch List


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Planning and Administration Guidelines

Performance characteristics of an operating system are dependent on such factors as:

Hardware Number of users during peak periods Functions being performed by the system System parameters

The three general tasks for improving your z/VM system efficiency are:

Planning Monitoring Performing


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Performance Considerations

There are two areas of performance to consider: The performance of individual virtual machines

The performance of the total system The total system performance achieved in a virtual machine

environment may be equal to or better than the performance achieved in a native environment.

Current processor usage is the most important factor in determining the performance that will be achieved in a virtual machine environment.


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Major Factors Affecting Performance

The interrelationship of the following factors affect total system performance:

The speed and number of paging devices

Real storage size

Real processor speed

Workload characteristics


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CP Performance Facilities

CP provides a set of performance facilities that can be used by individual virtual machines to improve their performance, such as:

Processor dedication option Virtual machine multiprocessing Virtual=Real (V=R) option Virtual=Fixed (V=F) option System scheduling control options


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CP Performance Facilities continued

Other performance facilities are: Scheduling share option Scheduling maximum share option Quick dispatch option Expanded storage allocation option Locked pages option Real channel program execution option Name saved systems (NSS) Saved segments


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CP Performance Facilities continued

Other performance facilities are: VM/VS handshaking

Interpretive-execution facility

Guest wait-state interpretation capability

Minidisk Caching

VM Data Spaces

Spool file initialization

File caching option for CP-accessed minidisks

Hot I/O Detection

Virtual Disk in Storage

I/O Throttling


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Performance Guidelines in a Virtual Machine Environment

There are some guidelines and hints that can be used to improve the performance of a virtual machine and its applications.

A list of such guidelines is provided to help explain the performance characteristics of a z/VM system.

The guidelines cover the actions taken to increase performance of both the z/VM environment and application programs.


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Performance Monitoring

Performance monitoring is the periodic collection of performance data and serves two major purposes:

Early detection of performance problems

Problem determination for performance problems The INDICATE and MONITOR commands provide system

performance measurement facilities for z/VM, which include: Obtaining system resource usage data

Collecting measurement data using a z/VM monitor for later analysis


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Performance Analysis Programs

z/VM supports additional performance analysis programs: IBM Realtime Monitor VM/ESA – used to help detect and

diagnose problems and analyze system performance VM Performance Reporting Facility – a tool for performance

measurement, analysis, and problem determination Performance Analysis Facility/VM – a graphics-based facility

that helps the performance analyst


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z/VM 4.4 Performance Toolkit

The Performance Toolkit for VM is designed to assist operators and systems programmers or analysts in the following areas:

System console operation in full screen mode:– The features provided have been designed to facilitate the operation of VM

systems, hence improving operator efficiency and productivity. These features include:

• General system output can automatically be scrolled; however additional privilege classes may be needed depending on implemented functions

• Messages and actions from other virtual machines are numbered and left pending at the top of the screen until explicitly deleted

• A redisplay facility allows browsing through the day’s accumulated console log, or through previous days’ logs


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INDICATE Command

This command provides the system analyst with a “snapshot” of system activities. Subcommands include:

INDICATE USER

INDICATE USER EXPANDED

INDICATE LOAD These commands can help determine the execution

characteristics of a program with respect to the resources it uses.


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INDICATE Command continued

Other commands that can provide a “snapshot” include: INDICATE QUEUES

INDICATE I/O

INDICATE PAGING

INDICATE VECTOR

INDICATE SPACES

INDICATE NSS


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Monitor Performance Using CP Monitor

The CP Monitor facility collects system performance data that can be processed by an external data reduction program.

The user controls the amount and nature of the data collected. MONWRITE can be used as the application program that establishes

communication links with CP and retrieves records. The monitor collects user-defined sets of statistics about z/VM

system operations that are saved in domains.


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Monitor Data

CP Monitor collects data during CP operations and stores the data collected in the saved segment.

Monitor collects and reports two types of data: Event data

Sample data, which is broken into:

– Single-sample data– High-frequency sample data

The system is divided into different domains for the purpose of collecting monitor data and generating monitor records.


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CP Monitor Commands

You would use the MONITOR command to control monitoring. Monitor commands include:

SET MONDATA QUERY MONITOR QUERY MONDATA

Monitor utilities include: MONWRITE MONWSTOP


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CP Monitor Facility

To use the CP Monitor facility, a virtual machine must run an application program to retrieve data from the monitor saved segment.

The *MONITOR system service can be broken into four parts: The virtual machine makes the connection

*Monitor notifies all applicable virtual machines that the records are ready to be retrieved

The virtual machine accesses the saved segment

*MONITOR notifies the virtual machine that it is finished


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Tuning Agenda

Tuning z/VM Tuning Methods Controlling the Dispatch List Allocating System Resources – Allocating Processors Tuning the Processor Subsystem Tuning the Paging Subsystem Tuning the Storage Subsystem Tuning the I/O Subsystem


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Tuning z/VM

Why tune your z/VM system? Performance tuning is undertaken when you want to:

Process a large or more demanding work load without increasing the system’s configuration

Improve system response or throughput

Reduce processing costs without affecting service to your users Tuning is basically trial-and-error, but there is a step-by-step

approach to any tuning project.


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Tuning Methods

The key states to record are: Running – CPU Wait

I/O Wait – Simulation Wait

Page Wait – Test Idle

Console Function Wait – Dormant

I/O Active – Active Page Wait

Limit List Wait


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Controlling the Dispatch List


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Allocating System Resources – Allocating Processors

Allocating system resources is a preliminary step to tuning your system.

CP allocates a V=R virtual machine one processor to the system and assigns each virtual machine the same share of processor time

To remove a dedicated processor from the V=R virtual machine, enter the UNDEDICATE command, which by default has a CPU ALL operand for the V=R user ID.


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Allocating System Resources – Using SET SHARE

This command and directory statement allows you to control the percentage of system resources a user receives.

A normal share attempts to provide the least amount of resources to a virtual machine.

A maximum share attempts to prevent a virtual machine from using more than the amount of system processor resource available. The types are:

NOLIMIT LIMITHARD LIMITSOFT


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Allocating System Resources – Using SET SHARE continued

In general, you should assign typical users relative share rather than an absolute share.

A relative share setting lets you determine the percentage of system resources a virtual machine gets with respect to other virtual machines with relative shares.


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Allocating System Resources – SET QUICKDSP

This command and operand of the OPTION directory allows you to designate virtual machines that will not wait in the eligible list when they have work to do.

The types of virtual machines that should be considered for QUICKDSP include:

The V=R virtual machine Other virtual machines with critical response-time requirements A production V=V guest that has interactive characteristics


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Tuning the Processor Subsystem

The resources of the processors installed at your location are referred to as the processor subsystem.

Some guidelines for reducing the load on your processors are: Reduce the amount of CCW translations

Reduce the SHARE settings To measure the workload, use these commands:

INDICATE LOAD

INDICATE QUEUES

INDICATE VECTOR


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Tuning the Processor Subsystem continued

The command to display the current interactive bias is: Query srm iabias

To change the interactive bias CP use: Set srm iabias m n

The SET SRM DSPBUF command lets you control the number of users in the dispatch list

This command lets you over-commit and under-commit resources of the processors and I/O devices.


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Tuning the Paging Subsystem

Paging is often the most influential component of overall response time.

To attempt to overcome a high paging rate, you should consider: Adding real storage

Adding expanded storage for CP to page to

Define more of your existing DASD as paging devices Display paging information using:

INDICATE LOAD

INDICATE PAGING


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Tuning the Paging Subsystem continued


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Tuning the Storage Subsystem

Waiting for storage to become available is a common cause of slow response time

To display information use the QUERY FRAMES command Use one of the following commands to control storage

allocation: SET RESERVED LOCK ATTACH XSTORE SET SRM STORBUF


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Tuning the Storage Subsystem continued


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Tuning the I/O Subsystem

Tune the I/O subsystem to determine what might be causing a system bottleneck.

Some guidelines for getting the best performance out of your system are:

Provide more real or expanded storage

Keep DASD volumes at a high degree of activity

Balance the activity on all DASD volumes

Reduce the number of I/O operations required per transaction To display I/O information, use the INDICATE I/O command.


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Tuning the I/O Subsystem continued

A subchannel measurement block is a control block that can be associated with a given device that contains measurement data

Three measurement components are: Connect time Function pending time Disconnect time

Some important ways to control I/O resource are: SET THROTTLE I/O Priority Queueing SET SRM DSPBUF SET SRM DSPSLICE


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Conclusion

Performance concepts help you set performance goals. When you configure your z/VM environment, use the INDICATE

and MONITOR commands to display and compare system characteristics.

The major goal for tuning your z/VM system is to optimize performance.


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Glossary

Channel command word (CCW): an instruction to an I/O processor (channel). Performance-oriented Assembler programmers used to code their own CCWs to improve efficiency.

Dispatch list: the virtual machines in this list are competing for the use of the real processors and all other scheduled system resources.


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Glossary

Dormant list: consists of the logged-on virtual machines that are not currently being considered for dispatching because they have no work to accomplish or are waiting for the completion of a long event.

Elapsed time slice: is the interval of time on a real processor that a set of virtual machines are competing for.

Eligible list: this list forms when there is more demand by virtual machines for real resources than are available


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Glossary

Event data: is collected and reported each time a designated system event occurs

Exclusive mode: in this mode, the virtual machine is the one, and the only one, connected to *MONITOR

INDICATE: this command provides the system analyst with a list of system activities

MONITOR: collects data during CP operations and stores the data collected in the saved segment in the form of monitor records


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Glossary

Sample data: is collected and reported at the end of each designated time interval

Share mode: any other virtual machine may connect to *MONITOR concurrently


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References

z/VM: Performance 4.3 – SC24-5999-02. URL: http://www.vm.ibm.com/pubs/pdf/hcsi1a50.pdf

Bitner, Bill. “z/VM Guest Performance: z/VM for zSeries Technical Conference V91”. April 8, 2002.

Bitner, Bill. “VM Performance Monitoring of Major VM Components”. February 22, 2001.

z/VM: Performance Report 4.3. IBM Corp 2002.

© 2004 ibm corporation ibm ^ z/vm module 9: performance

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