Subsystems

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Chapter 13

• Subsystems

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Basic Facts

• All work is carried out in a subsystem.
• All jobs are divided by type into subsystems.
• Subsystems are started when the AS/400 powers up
  and loads the Operating System.
• A way of organizing, in order to increase
  efficiency.

OFFICE
J O B S
3
Memory Activity Levels

• Activity levels -enhance raw memory allocation
  by restricting how many programs will vie for the
  same memory at the same time.

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Why limit activity level?

• Each job secures enough resources to run
  efficiently
• Too large of a number will force jobs to compete
  for system resources and ultimately slow
  completion of all jobs

5
Memory Storage Pools

• A storage pool is a pool of memory where one
  type of program or application (a set of
  programs) runs.

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Subsystems Are

• A subsystem is an environment unique to a type of
  program. It allows computer run-time attributes
  to be applied to all jobs within it, while other
  jobs in other subsystems keep their own
  attributes.

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Single Vs. Multiple Subsystem Configuration

• Single - QBASE
• The subsystem for all work active upon
  installation
• Convenient for installation
• Doesnt take advantage of systems capabilities

• Multiple
• Improves performance to separate workload
• AS/400 comes preloaded with basic 5 subsystems
• Change system value for QCTLSBSD to QCTL the
  AS/400 understands to start using multiple
  subsystems

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5 Basic Subsystems

• QCTL
• the controlling subsystem in a multiple subsystem
  configuration
• The system console is attached to this subsystem
• This is so the system console can carry out
  functions during IPL

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5 Basic Subsystems (cont.)

• QINTER
• Subsystem that supports interactive jobs
• QSPL
• Handles all spooled file jobs

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5 Basic Subsystems (cont.)

• QCMN
• Supports all communications jobs
• QBATCH
• Supports all batch jobs

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5 Basic Subsystems (cont.)

• The AS/400 allows for any combination of jobs
  within a subsystem. However, doing so will
  reduce the systems efficiency.
• The object, subsystem description, is required
  whenever a new subsystem is created.

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System Pools

• Also called a storage pool.
• A logical division of main memory reserved for
  processing jobs.
• Subsystems are pre-assigned to main memory pools
  by the Operating System.
• Work is divided into types of jobs (Just like
  types of pools).

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Storage Pool Characteristics

• Activity Level
• Max number of jobs that can be run simultaneously
  in the poolHow many lanes

• Pre-defined size
• number of bytes that can be stored in the pool
  How much water

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Shipped Storage Pools

• MACHINE is the storage pool where the system
  runs.
• BASE can be where everything else runs.

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Related System Values

• QMCHPOOL - Sets Size OF Machine pool.
• QBASPOOL - Sets minimum size of BASE pool.

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Portion of Memory

• A pool is the amount of allocated memory.

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Memory Management Concepts

• Paging is writing a inactive memory page to DASD
  so an active page can be read into memory.
• Faulting is when a program (or its data) attempts
  to access a page not in memory. It then is
  fetched.

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Memory Management Concepts

• Timeslice, is the period of time allocated for
  CPU usage by a job when it executes.
• Thrashing is excessive faulting.

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CPU Considerations

• Time Slices
• The amount of processor time a job has before the
  CPU moves to another job
• Run Priorities
• Within a storage pool, job with highest prior
  acquires system resources first
• Ex Print writers, then interactive jobs, then
  batch jobs

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CPU Considerations (cont.)

• Run Priority Vs. Job Priority
• Run priority is the priority of job while
  executing
• Job priority is the relative order of job waiting
  on job queue

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AS/400 Jobs Three States

• ActiveThe job is running. Job is occupying
  storage, using processor, and hasnt exceeded
  activity level.
• WaitThe job is waiting for something to happen.
  Waiting until next user request to start.
• Ineligible The job is ready to run, but the
  system is not available. Ineligible job cant
  occupy storage or processor due to activity level
  is at max.

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AS/400 Jobs Three States (cont.)

• Jobs shift between states automatically,
  depending on systems work load
• Job may need to become ineligible at end of its
  time slice

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Memory Pool Types

• Shared Pools
• Special shared pools. The two pools that come
  with the AS/400, MACHINE and BASE, are special
  shared pools. These are the only special shared
  pools.
• General shared pools.
• Private Pools
• Maximum pools 64 including BASE and MACHINE.

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Pre-defined Pools

• The AS/400 comes with predetermined names and, in
  two cases, predetermined uses, for shared pools.
• Here is the list
• INTERACT Supports interactive subsystems jobs.
  
• SPOOLSupports spool writers (printing).
• SHRPOOL1 through SHRPOOL60 Names available for
  customer-defined shared pools.

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Creating Private Pools/ Assigning Shared Pools
Create Subsystem Description
(CRTSBSD) Type choices, press Enter.
Subsystem description . . . . . _______
Name Library . . . . . . . . . . .
CURLIB Name, CURLIB Storage pools
___ Pool identifier . . . . . .
. _________ 1-10 Storage size . . . . .
. . . . _________ Number, BASE, NOSTG...
Activity level . . . . . . . . _______
Number for more values
_________ Maximum jobs . . . . . . . . . .
NOMAX 0-1000, NOMAX Text 'description'
. . . . . . . BLANK   

Bottom F3Exit F4Prompt F5Refresh
F10Additional parameters F12Cancel
F13How to use this display F24More keys
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Changing Pool Memory/ Activity Levels

• Three commands that change memory and activity
  level settings on pools.
• They are
• Work with System Status (WRKSYSSTS)
• Change Subsystem Description (CHGSBSD)
• Change Shared Pool (CHGSHRPOOL)

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Changing Pool Memory/ Activity Levels (cont.)

• There are also two system values that affect
  memory pools and activity levels
• Machine Pool (QMCHPOOL)
• Base Activity Level (QBASACTLVL)

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Table 13-1 Memory Activity Level Commands
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CHGSHRPOOL command
Change Shared Storage Pool
(CHGSHRPOOL)

Type choices, press Enter.


Pool identifier . . .
. . . . . __________ MACHINE, BASE,
INTERACT... Storage size . . . . . . . . . .
SAME Number, SAME, NOSTG
Activity level . . . . . . . . . SAME
Number, SAME Paging option .
. . . . . . . . SAME SAME, FIXED,
CALC Text 'description' . . . . . . .
SAME                                 
__________________________________________________
__________________________

















Bottom F3Exit F4Prompt F5Refresh
F10Additional parameters F12Cancel
F13How to use this display F24More keys
Figure 13-2 CHGSHRPOOL command

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Private Pools Changed Within Subsystems
Figure 13-3 CHGSBSD command to change private
pool sizes.
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Work with Subsystems (WRKSBS)
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WRKSBS Display Pool Definitions
Figure 13-5 Command WRKSBS, displaying pool
definitions.
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Work with System Status

Figure 13-6 Command WRKSYSSTS, information about
system pools.
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Work Shared Pools
Figure 13-7 Command WRKSHRPOOL.
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Subsystem Description
Figure 13-8 Prompted CRTSBSD command.
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Add Storage Pools to Subsystem
Figure 13-9 Adding storage pools to a new
subsystem description
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Routing Entries
Figure 13-10 A sample of the routing data for a
job description.
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Routing Entries (cont.)
Figure 13-11 Routing entries in the subsystem
description.
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Routing Entries (cont.)
Figure 13-12 Expanded routing entries in the
subsystem description.
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Workstation Entries

• AS/400 workstations are devices (Interactive Jobs
  Only)
• Job Queues
• Autostart Jobs
• Communication Jobs
• Pre-start Jobs

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Starting Subsystems
Figure 13-13 Prompted STRSBS command.
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Ending Subsystems
Figure 13-14 Prompted ENDSBS command.
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Basic Work Management Structure
   
 
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