Re: Required Metrics

[Robert Dewar <robert_dewar@my-deja.com>]

The trouble with documentation requirements is that the
standard, by necessity, does not define exactly what the
meaning of these requirements is, or even what documentation
consists of.

In the case of typical implementations on top of an operating
system, about the best documentation of the conventional kind
that you could give for tasking metrics would be to clearly
document the sequence of operating systems calls that is made
for any particular tasking language construct.

Our view in the case of GNAT is that the sources of the run-time
which are an integral part of our complete technical
documentation contain precisely this information, and so far
we have not had any instances of users requiring the information
in any other form.

I don't think this is so surprising. We could of course run
benchmarks on particular machines under particular conditions
and publish numbers that appear to meet the requirements of
the RM. Why "appear"? Because in practice they won't be useful
for users. If users need hard figures on timings of tasking
operations, what we would advise is that they run tests
corresponding to their actual use of tasking constructs in
the exact conditions they will be using them. This is the
same advice that applies to any use of any features of the
language.

I personally think the metrics requirements in annex D do not
belong in a language standard. They are too vague from a formal
point of view, and not helpful from a pragmatic point of view.

Historically they were put there to satisfy people who actually
wanted to try to quantify performance with specific RM
requirements for performance, keyed to processor clock speed.
That's of course an even WORSE idea for infusing the standard
with inappropriate junk :-)

Robert Dewar
Ada Core Technologies


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