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From: trickey@alice.UUCP
Newsgroups: comp.lang.lisp
Subject: Common Lisp Performance Analysis
Message-ID: <6632@alice.uUCp>
Date: Tue, 10-Feb-87 21:18:29 EST
Article-I.D.: alice.6632
Posted: Tue Feb 10 21:18:29 1987
Date-Received: Thu, 12-Feb-87 02:26:07 EST
Organization: AT&T Bell Laboratories, Murray Hill NJ
Lines: 33


What do people do to find out where the time is going in a
large common lisp program?  I recently cut the run time of
a large compiled-lisp program by a factor of 5 by finding
out that my elegant general all-shortest-paths finding
routine (taking a node list and adjacency function, returning
functions for the shortest path and length between pairs)
was taking 90% of the time, and needed replacing by a faster
specialized one that left the answer in a global.

I found this by inserting calls to get-internal-cpu-time in
various places.  But it seems like there should be something
like the time profiling we're used to with C, etc.  It seems
possible to put in a SYSCALL of profil (I'm using Lucid
Common Lisp 1.2, on a Sun), and analyzing the results.
(Garbage collection should be turned off, assumptions made
about how the loader loads .lbins).  Has anyone done this?

It's possible to redefine defun to accumulate counts, or even
times, but the timing resolution isn't fine enough for the
latter to work for all but the longest functions.

You might be interested to know that I've implemented the
same program (a graph layout program) in Common Lisp and
C++, about 8000 lines each.  The C++ version is now 2 to 3
times faster (it was 10-20 times faster before I discovered
the shortest-paths thing, about the only place where there was
a significant difference between the two versions).  This
is better than I expected for Common Lisp.  I think it is because
so much time is spent doing shortest paths, and I spent time
making the CL version as fast as possible.

Howard Trickey, AT&T Bell Laboratories {allegra,research}!trickey