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Date: Sun, 11 Jul 2010 20:47:41 -0400
From: "Peter C. Chapin" <pcc482719@gmail.com>
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Subject: How many hardware threads?
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Date: 2010-07-11T20:47:41-04:00
List-Id: <comp.lang.ada>

As we all know there is currently a lot of "buzz" about parallel
programming and about the "crisis in software development" that is
associated with it. People using languages with weak support for
concurrency are now wondering how they will use multi-core systems
effectively and reliably. Of course Ada already has decent support for
concurrency so part of the problem is solved for those of us using Ada.

But not all of the problem...

I see a couple of difficulties with writing effective parallel programs
for "ordinary" applications (that is, applications that are not
embarrassingly parallel). One difficulty is load balancing: how can one
decompose a problem to keep all processors reasonably busy? The other
difficulty is scalability: how can one design a single program that can
use 2, 4, 16, 128, or more processors effectively without knowing ahead
of time exactly how many processors there will be? I'm not an expert in
Ada tasking but it seems like these questions are as big a problem for
Ada as they are for any other language environment.

I'm not looking for a solution to all tasking problems here. But there
is one feature that seems like a necessary prerequisite to such a
solution. The language (or its standard library) needs to provide a
portable way for the program to determine how many hardware threads are
available.

I'm about to write a simple program that decomposes into parallel,
compute-bound tasks quite nicely. How many such tasks should I create? I
could ask the user to provide the number as a command line argument or
in a configuration file. Yet it seems like the program should just be
able to figure it out. Does Ada have a standard way of doing that? I
didn't see anything in my (admittedly short) review.

Thanks!

Peter