🚀 go-pugleaf

On 10 Dec 92 19:18:35 GMT, rschnapp@metaflow.com (Russ Schnapp) said:

rschnapp> (Bradley R. Carlile) writes:

Bradley> The limit of 4 or 6 may be the limit programming a superscalar
Bradley> chip like by simply letting the the chip group instructions
Bradley> together.  *However* if one uses the technique of software
Bradley> pipelining like we used to use on the VLIW machines of
Bradley> yesteryear FPS-120B (before 1976), FPS-164, and the FPS-264
Bradley> (1985?).  These machines could issue up to 10 instruction every
Bradley> cycle {I wrote software for 7 years that used these
Bradley> instructions}.

rschnapp> Don't forget about out-of-order (i.e., dataflow) execution
rschnapp> techniques.  You can gain plenty of additional fine-grain
rschnapp> parallelism.

Ah, there are indeed many interesting tricks to support high levels of
micro parallelism *in the implementation*. To me the really interesting
problem is not how to do it, though, it is whether it is worth doing it,
and for which classes of codes.

I have yet to find evidence that *general purpose* codes have an
intrinsic degree of micro parallelizable operation (let's call it
superscalarity) that makes it worthwhile to have a degree of parallel
*instruction issue* within a single stream not greater than 2-4.

  The codes that can be easily micro-parallelized are usually *special
  purpose*, in that they have a structure (e.g.  FIFO reference patterns)
  that are best suited to a SIMD/vector processor approach.

Otherwise *general purpose* codes have a degree of macro parallelism
(let's call it multithreading) that can be best exploited with multiple
CPUs, and that can exploited up to a degree of parallel *instruction
streams* with independent contexts not greater than 2-4 (again).

  Then are are codes that can be easily macro-parallelized, and these
  are again *special purpose*, in that they have a structure (e.g.
  LIFO reference patterns) that are best suited to a MIMD approach.

Naturally all this depends on how you define a "code"; for example a
timesharing system might be considered a single, highly parallelizable
code, or as a collection of fairly hard to parallelize different codes.
--
Piercarlo Grandi, Dept of CS, PC/UW@Aberystwyth <pcg@aber.ac.uk>
  E l'italiano cantava, cantava. E le sue disperate invocazioni giunsero
  alle orecchie del suo divino protettore, il dio della barzelletta