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From: wagner@utcs.UUCP
Newsgroups: comp.sys.amiga
Subject: Amiga Multi-tasking Overhead
Message-ID: <1986Dec2.102542.4658@utcs.uucp>
Date: Tue, 2-Dec-86 10:25:42 EST
Article-I.D.: utcs.1986Dec2.102542.4658
Posted: Tue Dec  2 10:25:42 1986
Date-Received: Tue, 2-Dec-86 10:39:51 EST
Organization: University of Toronto Computing Services, general purpose UNIX
Lines: 33
Checksum: 37661

I've heard it said on the net that, when idling, an Amiga is using about 17%
of the CPU (at least in my case, the numbers seem worse, but that's another
problem).  I've also heard it said that this is the price for multi-tasking.

The more I think about this, the less likely it seems.  People have often
criticized large mainframe operating systems like MVS for using up 3 or 4
% when idling.  In MVS's case, there is a small amount of timer-interrupt
driven performance monitoring going on all the time.  In the case of the
Amiga, some work is being done every vertical retrace time, to set up the 
copper.  But 17%? ...

So I did some simple experiments.  It happens even for simple screens.
It happens even at the very beginning
of boot (well, once one can ^D out of the boot process).  It decreases
if you take out one of the disks, and, on close examination, the clicks
correspond to times when the CPU load *goes down*!.?!  Does this mean that
some disk-related software is polling?  Whatever for?  The disks are nice,
interrupt-driven things, aren't they?  

I have a simple performance monitor tool that I got from someone in the
Toronto area.  It produces a bar-chart sort of display of CPU and memory
use (its real handy, as far as it goes).  (It's Icon is a cute little 
rabbit, but, once again, that's another story).  What I'd really like 
now is a tool that told me which task/process was using how much of
the CPU.  Does such a thing exist?

The search for answers continues.

Michael
P.S. The monitor I have deduces CPU busy by putting a subservient, 
low-priority task into a loop.  There are two fields in the EXECBASE
structure for counting idle and dispatched time slices.  Are they not
good enough, somehow?