© 2004 IBM Corporation IBM ^ z/VM Module 9: Performance

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ Virtual Machine Scheduling Flow

© 2004 IBM Corporation IBM ^ Four Transaction Classes: Eligible List

© 2004 IBM Corporation IBM ^ Dispatch List

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ INDICATE Command continued  Other commands that can provide a “snapshot” include:  INDICATE QUEUES  INDICATE I/O  INDICATE PAGING  INDICATE VECTOR  INDICATE SPACES  INDICATE NSS

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ Controlling the Dispatch List

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ Tuning the Paging Subsystem continued

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ Tuning the Storage Subsystem continued

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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.

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ 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

© 2004 IBM Corporation IBM ^ References z/VM: Performance 4.3 – SC URL: Bitner, Bill. “z/VM Guest Performance: z/VM for zSeries Technical Conference V91”. April 8, Bitner, Bill. “VM Performance Monitoring of Major VM Components”. February 22, z/VM: Performance Report 4.3. IBM Corp 2002.