Ada vs C/UNIX / switching speeds

[Ted Holden]

Sometimes, these arguments get off track so badly that the
non-initiated might lose their bearings following them.  Remember,
it is Ada and not C or C++ which makes the mistake of having
tasking be part of a programming language rather than part of an
OS or a library.
 
From:  Bill Wolfe, Clemson
 
>  The following article relates to the recent discussion
>  of Ada vs. UNIX/C and lightweight processes.  Notice the
>  disastrous performance produced by UNIX/C relative to Ada.
 
>Date: Fri, 17 Nov 89 11:03:44 CST
>From: steve at titan.tsd.arlut.utexas.edu (Steve Glicker)
>Subject: Simple process and task switching speeds
 
>Recently there have been references to lightweight processes, UNIX/C
>processes, and Ada tasking in terms of speed (Bill Wolfe on Date: 15
>Nov 89 16:06:41 GMT and Walter Rowe on Date: 16 Nov 89 18:20:01 GMT).
 
>Over the last few months, I have been collecting numbers on
>task/process switching speeds.  Several tests have been run were two
>tasks or processes invoke each other several hundred thousand times,
>execution time is then divided by switches...
 
>The information I have collected is in the following table.  This is
>quite informal -- these are rough estimates.  Does anyone have
>estimates on the speed of lightweight processes, etc.?  Data on
>embedded systems is welcome.  I would also appreciate any references
>to work published on this topic.
 
> Platform        Test             Switching Speed
>==============  ================ =================
>microVAX (VMS)  VMS processes    ~ 0.6  ms
>microVAX (VMS)  DEC Ada tasks    ~ 0.6  ms
>Sun 3/50 (UNIX) Function call    ~ 0.01 ms
>Sun 3/50 (UNIX) Simula processes ~ 0.2  ms
>Sun 3/50 (UNIX) Verdix Ada tasks ~ 0.3  ms
>Sun 3/50 (UNIX) UNIX/C processes ~10.0  ms
 
>I understand that the microVAXs ran at ~0.9 VAX 780 MIPS and the Sun
>3/50 at ~1.5 VAX 780 MIPS.  In the cases of Ada and Simula a scheduler
>supplied with the language was used.
 
Did I ever say anything about implementing a real-time or embedded
system in vanilla UNIX?  Did any of the C or UNIX gurus on the net?
I mean, I like UNIX, but I'm not stupid;  that's about the only thing I
can think of which would actually be as pathalogical or more
pathalogical than writing a real-time or embedded system in Ada.
 
Vanilla UNIX is taking the world by virtue of portability (no other OS
has it), not real-time features.  It is intended most primarily as a
software development platform.  Real-time/embedded systems should
ideally be written in C or C++ on a UNIX system and then run either on a
real-time kernel like VRTX or on a modified UNIX system such as is
sold by Masscomp or Charles River.  Serious database applications are
best run under UNIX on UNIX systems which have been specially modified
and/or designed therefor, e.g. Sequent or Tolerant.  I am not totally up
on UNIX V/4;  it might be that V/4 will have some of these same kinds of
capabilities.
 
I know, I can hear it:  "what about standards?"
 
Bjarne Stroustrup said it best recently:
 
>Anyway, most C++ standardization problems arise because C++ has several
>independent implementations. This is a problem of succcess; most languages
>never get a second implementation: their application areas and user
>base simply never grows to make a second (or a tenths) implementation
>viable.
 
Same holds for UNIX.  In the case of a big-time loser like Ada, on the other
hand, one version is all that most of mankind needs to see.  Bjarne was
too polite to say that;  a barbarian such as myself, obviously, has no
such inhibitions.
 
All of which still leaves the UNIX/C/C++ idea far more usable than Ada.  A
vast majority of software will still be easily portable from the
MassComp, through vanilla UNIX, to the Sequent.
 
By the way, I still can't get over the manner in which one of the Ada
advocates on the net ended his refutation of my most recent anti-Ada
diatribe:
 
From: Marc Lewis: U. of Nebraska at Omaha
 
>My only problem with Ada at this point is the cost ($ and hardware
>resources) of a compiler for my XT clone.  Both IntegrAda and Janus
>require more memory than DOS 4.01 leaves available.  This is BAD DESIGN.
>There is no excuse for a 551K executable in a PC (pass 2 of Integrada).
>Janus Ada requires >580K available to run, and rumor has it that the
>Integrada compiler is a repackaged Janus compiler.
 
Which is almost better than anything I could think of to say on the
topic.  With advocates like this, the Ada group probably doesn't even
need me around;  I can get back to talk.origins where my talents are
appreciated.
 
Ted Holden
HTE
 
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