Compilation of methods per class.

[Jon L White <jonl@lucid.COM>]

re: I couldn't illustrate any significant differences in run times with
    this test file in Franz, though I do get them (up to 10 times slowdown,
    as I do in Lucid) with my large program that has some generic-functions
    specialized on over 20 different classes with a number of variable mixins
    on run-time classes.

This is precisely the symptom of the "cache assumption breakdown."
Namely, you probably can't get the identically same example to be the
breakdown case in two different implementations of Lisp, because
just the slightest change in "hashing numbers" used for the overall
technique will skew the distribution of entries in the cache.  There
is a verrrry non-linear change here for just a trivial skew.

The other relevant tidbit is the factore of 10; that is exactly the
slowdown factor I observed several years ago when first noticeing
the "assumptions breakdown" problem.  Compare this factor with the
following numbers.

re: Another question brought up by all this is why generic function calls on
    classes that have :arounds with one call-next-method take so much longer
    than calls on classes that only have a primary?  E.g. fast-foo on class11
    here takes 5x as long (3x as long in Franz) as fast-foo on class1 (0.104 msec
    vs 0.019 msec).  Isn't all of the "hard" work done in looking up the
    effective method for a class in the first place? If the effective methods
    were computed and stored for each run-time class, then a call-next-method
    should (basically) involve primarily an additional funcall of a (known)
    next method function, which should be trivial in comparison to the
    effective-method-function lookup done by the generic function.

You are right in your analyses here -- the observable slowdown ought to be
the extra layer of function-entry-and-argument-collection, and subsequent 
argument-re-spreading-and-function-apply.  In this arena, the observable 
time differences between a "very best" port of the PCL technology and a 
"pedestrian" port ought to be in the range of the 3-to-5 that you saw at 
the micro level between Franz and Lucid on the Sun4.


-- JonL --