AppendixA.Performance
The following sections describe the performance that can be achieved with several
S/390 workloads. Since performance of the IBM S/390 Integrated Server depends
on the type of work being run on the machine, you should focus on the
performance for a workload that is most representative of your actual work.The
information supplied in the following paragraphs will assist you in determining the
performance you can expect.
MVS and OS/390 Performance
TSOPerformance
The TSO workload can be considered a storage intensive workload and with the
256MB of “on-board” storage for the P/390 adapter up to 90 users can be
supported.
This TSO workload is designed to represent the work done by a TSO end-user
community developing and testing programs interactively using ISPF/PDF.
Workload activities include editing and browsing source data, compilation,
execution, program testing, graphics, and information management transactions.
There are 25 different scripts, each consisting of a related set of activities in the
form of TSO commands.CLISTS are implicitly and explicitly invoked.The think
time is exponentially distributed with an average of 15 seconds between scripts and
the internal response time limit is 2 seconds.Compile and assembly operations
comprise about five percent of the TSO workload.When workloads with a higher
percentage of these operations are encountered, fewer users can be supported.
While the internal response times achieved by the IBM S/390 Integrated Server are
within the specified limits, other S/390 processors, due to their standard I/O design
point, typically yield lower response times.Since internal response time is one of
several factors that contribute to end-user response time, there may be some
instances where end user times are longer than those achieved by other S/390
processors. There are many instances, particularly in remote applications, where
use of the IBM S/390 Integrated Server can eliminate or reduce other time
components to yield net improvement in overall response time.
As mentioned previously, the capacity of the IBM IBM S/390 Integrated Server is
determined by the type of work being run.One of the key characteristics of “work”
is I/O content. While the TSO workload described here contains a relatively light I/O
content when adequate amounts of storage per user are present, paging I/O can
become significant when the number of users is increased beyond a certain
threshold. When paging I/O becomes significant, total I/O can exceed the I/O
capability of the machine and response times will increase.The supported number
of users is determined by the number of users at which either excessive paging
occurs or the processor becomes saturated.However, with 256MB's of storage for
the P/390 processor, the processor will generally become saturated before
excessive paging occurs.
The maximum number of users supported for a storage size and think time is
related to the working set size for the average user, which is approximately 1MB for
 Copyright IBM Corp. 1998 29