Hi Felix. I did not mean to drag you into this discussion. I know
performance benchmarking is one of your buttons that is best left
untouched!
All of this started with this message on the Gambit mailing list about
the performance claim that call/cc in Chicken was "free" because of
Cheney on the MTA and that Gambit used the same approach:
On 24-Sep-08, at 11:14 AM, Per Eckerdal wrote:
Chicken. Cheney on the MTA gives you call/cc essentially
for free - it's just as fast as any other function call.
I was under the impression that Gambit also did this.. Am I wrong?
/Per
My response was that Gambit's continuations are based on a completely
different approach which gives just as good performance, using the
ctak and fibc benchmarks as simple evidence. A complete analysis of
the two approaches would take a lot of effort, which is why I used
these benchmarks as a quick-and-dirty way to evaluate the performance
(it turns out that ctak is much better than fibc as a benchmark for
call/cc because fibc does many other things than just call/cc, i.e. it
measures other optimizations of the compiler).
Let me reiterate that I'm not trying to compare Gambit and Chicken as
systems. If that was the case I would have much more to say and
obviously would conclude that Gambit is better ;-)
Marc
On 27-Sep-08, at 9:03 AM, felix winkelmann wrote:
On Fri, Sep 26, 2008 at 5:32 PM, Marc Feeley
<[EMAIL PROTECTED]> wrote:
The conclusion from my benchmarks is quite different. Chicken does
not
outperform Gambit on these benchmarks. There is so little other
stuff
happening than call/cc in these benchmarks that it would appear
that the
performance of call/cc in Chicken and Gambit is essentially the
same (to
within a few percent).
Why not simply say: chicken and gambit are roughly in the same
ballpark?
In the end, I have learned that nearly every performance assumption
I made
was wrong, and I'm a pretty experienced Scheme coder. Performing
benchmarks
like this and trying to extract any kind of practical relevance from
the fact that
program X on implementation Y with optimization settings Z takes 2%
longer than
on implentation Q. Are you sure you have built both implementations
with
maximal performance settings? Have you measured how much runtime-
performance
the memory patterns in this particular benchmark have caused? How do
you know
how your system configuration and hardware setup influences the
outcome?
Have you used optimal optimization settings for all implementations
for this
benchmark? Have you analyzed the compiler output to look for
opportunities
to tweak those settings for this particular benchmark? Do you know
enough
about chicken's internals and compiler options to chose the optimal
combination
(you couldn't, just as I couldn't for Gambit). It's all just
assumptions.
The very reason Scheme and Lisp have so little acceptance and are
not more
widespread is that its implementors are so obsessed with performance
(for
hystorical raisins, of course), instead of making their implementation
easier to work
with, more practical and more useful.
Nevertheless I understand this obsession, its lots of fun, after
all. :-)
So: CheneyOnTheMTA is an elegant concept that unifies fast first-class
continuations, fast allocation, generational GC and not-too-
difficult FFI
in a relatively simple framework. Chicken's compiler is sufficient,
but there are
many opportunities to improve performance, some of which will be
addressed, but which aren't really that important. A real module
system
(soon to come!) and 400+ libraries is what will make users happy,
not 5% better
performance.
I believe that CheneyOnTheMTA is more memory-efficient than other
Lisp-implementation techniques. I also believe that the CPS-output of
this scheme
is more C-compiler friendly and easier to compile on stock machines.
I believe
that COTMTA (that's a nice abbreviation - I think I'll use that from
now on) makes
cross-module calls more efficient than trampoline-style, which is
important
for large code-bases that use separate compilation and dynamically
loaded
plugins. These are all assumption that may possibly be completely
wrong.
Keep up the good work, Marc! Gambit is cool. But chicken is
better. ;-)
cheers,
felix
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