Re: Realtime Ada Conferences

[dewar@cs.nyu.edu (Robert Dewar)]

Ed Falis said

"I think your info about context switching time is out of date.  Here's
some sample PIWG data for our ActivAda Realtime product, an Ada 83
compiler for 32 bit Intel x86 processors.  The benchmarks were run with
checks on and optimizations on.  The target is a 75MHz 80486 DX4.
"

Note that these context switch times are for simulated context switching
(i.e. threads simulation), rather than for use of operating systems
threads. Of course that's all you will get on DOS/Windows type
environments, so that's certainly not a criticism!

But you need to be very careful about comparisons here. One of our GNAT
customers was surprised to find that GNAT context switching time was
much better on SunOS than on Solaris -- yes of course, because on Solaris
we use the operating system threads, which are supposedly "lightweight"
but still slow, and on SunOS, we do our own simulated context switching.

Most people want to use real threads when running over an OS that has
real threads, and for example, I am sure that the new Thompson compiler
for Win NT will have this capability. 

We actually can run Solaris with simulated threads as well, but for
simplicity only support the "real" threads version.

A nice capability in the old Alsys technology, which I would expect to
carry over to the new Thompson technology is a very flexible way of
spefiying mapping tasks to threads, with 1-1 (use all OS threads)
and all-1 (simulate all threads) just being two extremes of a very
flexible way of specifying the mapping. I will let Ed say more
about this!

Robert Dewar
Ada Core Technlogies

P.S. there are two Robert Dewar's around, the general Ada gadfly who
comments on all sorts of CLA issues, and the president of ACT, who
at least to some extent is speaking for ACT. The latter signs his
name as above, so you can distinguish! 

Both Dewar's do their best to get their facts straight and to speak only
THE TRUTH, but feel free to yell at either of them if you disagree :-)