Re: Using Global Variables

[seas.gwu.edu!mfeldman@uunet.uu.net (Michael Feldman)]

In article <1992Sep18.235238.25207@nosc.mil> sampson@nosc.mil (Charles H. Samps
on) writes:

[stuff deleted]

>So, my question now is: For those real-time systems for which global vari-
>ables are used instead of expensive parameter passage, was that decision
>based on inherent limitations of the hardware, lack of cleverness by the
>compiler writers, or poor analysis of the actual costs of parameter pas-
>sage?
>
In my very limited experience working with real-world real-time people,
it's been mostly the last. There's a lot of folklore in real-time systems.
One of the bits of folk wisdom is "parameters are expensive; globals
are cheap." It's easier to just rely on the folk wisdom than to actually
analyze or measure.

Two bits of _my_ folk wisdom:

(1) Fast enough is fast enough. Tweak (only) what you need to tweak.

(2) It's easier to make a correct program fast than to make a fast program
    correct.

Mike Feldman