Re: lists.texi

[Luc Teirlinck]

My test case constructed ten thousand times a list of size 1000,
triggering a lot of garbage collections.  In a freshly started Emacs,
the ring-elements function I propose to install ran the test in 11
seconds, slightly over 5 being spent in gc.  This gives between 5 and
6 for the function itself.  The "abstract" version ran 37 seconds, a
little bit over 5 in gc, giving 31 to 32 for the function itself.  In
other words, avoiding the `ring-ref' overhead makes the function run
more than five times faster, but the amount of consing stays the same.

If I run the same test in a somewhat older Emacs, the functions
themselves still take 5 to 6 and 31 to 32 seconds, but now they both
spend 17.5 seconds doing gc (instead of slightly more than 5).

I guess that in a really big Emacs, gc will take even much longer.  It
is not very surprising that the more objects gc has to check, the
longer it takes.  I believe this pretty much explains the gradual
slowdown of Emacs as it grows older (and hence bigger).

Sincerely,

Luc.