[pthreads] performance test using fib.scm

[Mikael Djurfeldt]

In the announcement of the pthreads support, I attached a program
fib.scm:

(define (par-fib n n-forks)
  (cond ((<= n 1) 1)
        ((> n-forks 0)
         (letpar ((f1 (par-fib (- n 1) (- n-forks 1)))
                  (f2 (par-fib (- n 2) (- n-forks 1))))
           (+ f1 f2)))
        (else
         (let ((f1 (mono-fib (- n 1)))
               (f2 (mono-fib (- n 2))))
           (+ f1 f2)))))

(define (mono-fib n)
  (let iter ((f1 1) (f2 1) (i 1))
    (if (>= i n)
        f2
        (iter f2 (+ f1 f2) (+ 1 i)))))

When I run this with a Guile compiled with COPT threads, it invariably
takes around 12 s to run (par-fib 40000 1) on my dual CPU machine.
"Top" reports 50% of CPU capacity usage during calculation.

With the new pthreads support (which now allows for real SMP), it
takes 2.6 s and top says 91%!

Still, for large fibonnaci numbers and large branch depths (many
threads), Guile often crashes in realloc.  That function should be
thread safe, shouldn't it?  Maybe we're trashing up the heap somewhere
else...

Anyone keen on some debugging? :-)

Mikael