V4R1 Server Model Performance Enhancement Clarification

[Neil Palmer <NPalmer@xxxxxxxxxxx>]

In response to several recent postings regarding performance of server 
models, and especially the changes in V4R1, I thought I would post 
informational APAR II10762.


APAR Identifier ...... II10762
OSP-PERFM SERVER MODEL PERFORMANCE ENHANCEMENT CLARIFICATION

ERROR DESCRIPTION:
OS/400 V4R1 Server Model Performance Enhancement Clarification

o Overview of New V4R1 Server Model

  AS/400 Advanced Servers and AS/400e servers are intended for
  use primarily in client/server or other non-interactive work
  environments.

  5250-based interactive work can be run on these servers, but
  at a reduced performance level.

  Beginning with release V4R1, the user has enhanced control
  over the impact of 5250-based interactive work on the
  non-interactive work on all RISC server models.

  The intent of this new enhancement is to reduce the impact
  of interactive jobs on non-interactive jobs.
  (For example client/server)

  To fully enable this new enhancement, customers MUST use a
  NON-INTERACTIVE job run priority (RUNPTY parameter) value of
  35 or less (which  raises the priority, closer to the default
  priority of 20 for interactive jobs).

  Changing the existing non-interactive job run priority can
  be done either through the Change Job (CHGJOB) command or by
  changing the RUNPTY value of the Class Description object
  used by the non-interactive job.  This includes IBM-supplied
  or application provided class descriptions.

  Examples of IBM-supplied class descriptions with a run priority
  value higher than 35 include QBATCH, QSNADS, and QSYSCLS50.
  You should consider changing the RUNPTY value for QBATCH and
  QSNADS class descriptions or changing subsystem routing entries
  to not use class descriptions QBATCH, QSNADS, or QSYSCLS50.

  If you modify an IBM-supplied class description you are
  responsible for ensuring the priority value is 35 or less after
  each new release or cumulative PTF package has been installed.
  One way to do this is to include the Change Class (CHGCLS)
  command in your system Start Up program.

  NOTE: Several IBM-supplied class descriptions already have
  RUNPTY values of 35 or less.  In these cases no user action is
  required.  One example of this is class description QPWFSERVER
  with RUNPTY(20).  This class description is used by Client Access
  database server jobs QZDAINIT (APPC) and QZDASOINIT (TCP/IP).

  The following is a generalised description of how interactive
  work is managed on AS/400 RISC server models.

  On Advanced Server models interactive jobs cause a non-linear
  increase in system overhead (measurable via CFINT).
  As additional interactive workload is put on the system, the
  system overhead increases, resulting in less processing power
  available to handle the client/server jobs.  The effect is
  that all jobs on the system experience degraded performance.

  With the new V4R1 enhancement, when interactive jobs CPU
  utilisation exceeds a threshold where increases begin to have
  higher impacts on performance, the interactive jobs
  will be de-prioritised according to the Dynamic Priority
  Scheduler algorithm in effect (system value QDYNPTYSCD is set
  to 1, as shipped on all RISC systems).  The effect of this
  de-prioritisation is to effectively give non-interactive jobs
  relatively higher prioritisation over interactive jobs.  By
  initially setting the non-interactive job RUNPTY value to at
  least 35, the non-interactive job will start to have increased
  priority compared to interactive work.  By setting
  non-interactive job run priority to a value closer (for example
  25) to the initial interactive job run priority, the
  non-interactive job will more quickly achieve a relatively
  higher priority compared to the interactive work running with
  priority 20.

  In summary, with the enhancement introduced at V4R1, when
  interactive utilisation approaches the threshold of significant
  performance impacts, interactive job priority is automatically
  reduced. Over time this brings the interactive workload CPU
  utilisation below the threshold and gives priority to
  non-interactive jobs.

o Special Case Considerations for Server Model Interactive Work

  Interactive jobs with priorities 10-16 are an exception case
  with the V4R1 or later enhancements.  Their priorities will not
  be adjusted by the algorithm.  These jobs run at their specified
  10-16 priority.  THIS MEANS JOBS AT THESE PRIORITIES COULD
  ADVERSELY EFFECT THE INTENT OF THE NEW ENHANCEMENT.  CPU
  utilisation of these jobs will be allowed to increase similar to
  V3R6/V3R7 server model interactive work.

  As with V3R6 and V3R7, if only one interactive job is active,
  it will not cause additional CPU utilisation or have its run
  priority lowered.

  These exceptions enable customers to get maximum performance for
  special case interactive functions on server models.  It remains
  the customer's responsibility to manage these special cases in
  relation to any non-interactive work also active.

  If non-interactive jobs do not have their run priority set to 35
  or higher (lower RUNPTY value), for example, RUNPTY 50, the V4R1
  enhancement will still work but its effect will be greatly
  reduced.  Non-interactive throughput will only be slightly
  improved.

  More information on the server enhancement can be obtained from
  your IBM representative or your IBM Business Partner.


... Neil Palmer                                     AS/400~~~~~
... NxTrend Technology - Canada     ____________          ___  ~
... Thornhill, Ontario,  Canada     |OOOOOOOOOO| ________  o|__||=
... Phone: (905) 731-9000  x238     |__________|_|______|_|______)
... Cell.: (416) 565-1682  x238      oo      oo   oo  oo   OOOo=o\
... Fax:   (905) 731-9202         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
... mailto:NPalmer@NxTrend.com          http://www.NxTrend.com


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