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1994-04-11
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CPU Load Average Monitor
========================
Documentation for !CPUload desktop utility version 2.50 27-Feb-1994.
Issue: 2.50 28-Feb-1994, replaces: 0.10 24-Mar-1991
1.00 25-Mar-1991
2.00 08-Jun-1991
Author: David J Ruck
Copyright © DEEJ Technology PLC 1991 -1994
Overview
========
!CPUload is designed to graphically show the amount of work the CPU (ARM
chip) is doing, in the style of the X windows utility xload. It provides an
alternative to Acorn's !Usage, supplied on the original RISC OS Applications
Discs, with several major enhancements, including:
(1) More accurate calculation & display of CPU load.
(2) Fully re-sizeable in both height (load axis)
and width (time axis).
(3) User selectable update rate, 100ms to 5 seconds.
(4) 400 load average point store.
(5) Full automatic and manual scaling options.
(6) Uses a very low amount of CPU time in operation.
The CPU load average is calculated from the number of calls and amount of
time between the Window manager Wimp_Poll Idle events being delivered to
!CPUload, this is used to determine the responsiveness of the machine.
The calculated CPU load average is displayed as black vertical bars in the
!CPUload window. After every update period the window scrolls to the left
and another bar is plotted.
The display automatically scaled to accommodate the largest value currently
in the window. The update rate and manual scaling can be selected via a
menu.
Using !CPUload
==============
On starting !CPUload a window is displayed immediately, it does not install
an icon on the icon bar. The !CPUload window is slightly different from most
RISC OS windows, in that it does not have horizontal or vertical scroll
bars, but it does have toggle and resize icons on the right of the title bar
- these can be used to resize the window in the standard RISC OS manner.
!CPUload holds a large number of load average points, so increasing the
horizontal size of the window will reveal previous values which have
disappeared off the left of the window (if the program has been running long
enough). Increasing the vertical size will enable more detail to be shown,
by using a larger scale.
!CPUload menu
-------------
The !CPUload menu options and sub menus are described below.
Info Displays program information and version number.
Update The update sub menu is used to select an update rate
in centi-seconds (1/100 second). The default is 50cs
or 2 updates per second. Low values can be used to
monitor small bursts of activity, 500cs enables over
an hours worth of CPU load to be monitored with the
maximum window width.
Note: the size of the bars produced at the same load
average is not the same for different update rates.
Scale The scale of the window is shown by light grey
horizontal lines, these do not represent values, but
the number of times the height of the vertical bars
has been halved. Thus no lines is the default scale,
1 line = ½ scale,
2 lines = ¼ scale and
8 lines = 1/256th scale, etc.
The automatic scaling (Auto ticked) ensures that the
largest bar currently in the window will fit. The
scale will change if a new large bar enters the
window or the largest bar falls off the left of the
window. Adjusting the horizontal size of the window
will affect the scale depending on the values moved
in or out of the window. Adjusting the vertical size
can also affect the scale.
The problem with automatic scaling is that if a very
large load blip occurs, other bars will become much
smaller, losing detail. Selecting and entering a
value in the Max scale sub-menu will limit the scale
used, smaller scales will still be used if possible.
Selecting and entering a value in Fixed scale will
only allow this scale to be used. Both the Max scale
and Fixed scale values correspond to the number of
light grey scale lines displayed.
Quit Removes !CPUload, having the same effect as click on
the window close icon.
Programming advice
==================
One problem which RISC OS application programmer's face is deciding on the
amount of time that should be spent in idle processing - that is routines
that run in the background using the idle events returned by Wimp_Poll.
Choosing too low a time will make the program inefficient, but too high a
time is anti-social to other active applications, making the machine feel
sluggish.
Unfortunately the RISC OS Programmers Reference Manuals only state this
fact, and do not provide firm timing values. Using !CPUload, a reference can
be obtained against a standard test, such as running the C compiler in an
DDE task window. You can then tailor your program to produce a mean load
equivalent to this under the same conditions.
End of !CPUload.!Help