General Effect On System Performance Of The Paging; Factor Only - IBM System/370 145 Manual

1
System
performance
Figure 15.15.3.
Paging Overhead
Active I
~I
0 0 1 1 - - - - -
Passive paging - - -.....
I
- paging
---·~l
I
Virtwll-to-real storage ratio
I
I
I
I
Task
~,.......
deactivation
"
,
,
,
General effect on system performance of the paging
factor only
If the active-to-passive
p~ge
ratio for the system is low, as shown
in curve 3, the virtual-to-real storage ratio can be relatively high
when active paging begins. The performance curve stays flatter longer
as virtual storage is increased when the active-to-passive page ratio is
low. This situation can apply to ,an installation in which all executing
programs are structured such that .real storage requirements and page
faults are minimized.
An installation that continues executing all or
most existing programs as they are presently designed and that
structures new applications for most efficient operation (low active-to-
passive ratio) may be more common. Such installations may experience a
virtual-to-real storage ratio somewhere between the low and the high
extremes possible for a given job :stream, as shown in curve 2.
The amount of virtual storage used in a system can
be
increased in
several ways. First, the size of existing application programs can be
increased by the addition of new functions. Second, the level of
multiprogramming and/or multitasking can be increased. assuming other
required resources such as CPU time and I/O devices are available.
Third, the size of existing applic,ation programs can
be
expanded by (1)
restructuring programs with a planned overlay or a dynamiC structure to
take them out of these structures .and (2) combining two or more job
steps within a job into one logica.l job step. The active-to-passive
ratio of the additional pages the :system must handle will usually be
higher when the level of multiprog:rammi.ng is increased than when
existing jobs are restructured.
A Guide to the IBM System/310 Model 145 87