What performance increases can we expect as the Perl 6 implementations mature?

Question

Each time I have downloaded a new copy of Rakudo Perl 6, I have run the following expression just to get an idea of its current performance:

say [+] 1 .. 100000;

And the speeds have been increasing, but each time, there is a noticeable delay (several seconds) for the calculation. As a comparison, something like this in Perl 5 (or other interpreted languages) returns almost instantly:

use List::Util 'sum';

print sum(1 .. 100000), "\n";

or in Ruby (also nearly instant):

(1 .. 100000).inject(0) {|sum,x| sum+x}

Rewriting the expression as a Perl6 loop ends up being about twice as fast as reducing the range, but it is still a very noticeable delay (more than a second) for the simple calculation:

my $sum;
loop (my $x = 1; $x <= 100000; $x++) {$sum += $x}

So my question is, what aspects of the Perl6 implementation are causing these performance issues? And should this improve with time, or is this overhead an unfortunate side effect of the "everything is an object" model that Perl6 is using?

And lastly, what about the loop construct is faster than the [+] reduction operator? I would think that the loop would result in more total ops than the reduction.

EDIT:

I'd accept both mortiz's and hobbs's answers if I could. That everything is a being handled as a method call more directly answers why [+] is being slow, so that one gets it.

Answer 1

It certainly isn't because everything is an object, because that's true in a number of other languages too (like Ruby). There's no reason why Perl 6 would have to be magnitudes slower than other languages like Perl 5 or Ruby, but the fact is that Rakudo is not as mature as perl or CRuby. There hasn't been much speed optimization yet.

Answer 2

There are really various reasons why Rakudo is so slow.

The first and maybe most important reason is that Rakudo doesn't do any optimizations yet. The current goals are more explore new features, and to become more robust. You know, they say "first make it run, then make it right, then make it fast".

The second reason is that parrot doesn't offer any JIT compilation yet, and the garbage collector isn't the fastest. There are plans for a JIT compiler, and people are working on it (the previous one was ripped out because it was i386 only and a maintenance nightmare). There are also thoughts of porting Rakudo to other VMs, but that'll surely wait till after end of July.

In the end, nobody can really tell how fast a complete, well-optimized Perl 6 implementation will be until we have one, but I do expect it to be much better than now.

BTW the case you cited [+] 1..$big_number could be made to run in O(1), because 1..$big_number returns a Range, which is introspectable. So you can use a sum formula for the [+] Range case. Again it's something that could be done, but that hasn't been done yet.

Answer 3

I submitted these to Fefe's language competition in December 2008. wp.pugs.pl is a literal translation of the Perl 5 example, wp.rakudo.pl is far more sixier. I have two programs because the two implement a different subset of the spec. Build information is outdated meanwhile. The sources:

#!/usr/bin/env pugs
# Pugs: <http://pugs.blogs.com/&gt; <http://pugscode.org/&gt;
# prerequisite: ghc-6.8.x, not 6.10.x
# svn co http://svn.pugscode.org/pugs/
# perl Makefile.PL
# make
# if build stops because of haskeline, do:
#   $HOME/.cabal/bin/cabal update ; $HOME/.cabal/bin/cabal install haskeline

# learn more: <http://jnthn.net/papers/2008-tcpw-perl64danoob-slides.pdf&gt;

my %words;

for =<> {
    for .split {
        %words{$_}++
    }
}

for (sort { %words{$^b} <=> %words{$^a} }, %words.keys) {
    say "$_ %words{$_}"
}

---

#!/usr/bin/env perl6
# Rakudo: <http://rakudo.org/&gt; <http://www.parrot.org/download&gt;
# svn co http://svn.perl.org/parrot/trunk parrot
# perl Configure.pl
# make perl6

# Solution contributed by Frank W. & Moritz Lenz
# <http://use.perl.org/~fw/journal/38055&gt;
# learn more: <http://jnthn.net/papers/2008-tcpw-perl64danoob-slides.pdf&gt;

my %words;

$*IN.lines.split(/\s+/).map: { %words{$_}++ };

for %words.pairs.sort: { $^b.value <=> $^a.value } -> $pair {
    say $pair
}

---

These were the results in 2008:

$ time ./wp.pugs.pl < /usr/src/linux/COPYING > foo

real    0m2.529s
user    0m2.464s
sys     0m0.064s

$ time ./wp.rakudo.pl < /usr/src/linux/COPYING > foo

real    0m32.544s
user    0m1.920s
sys     0m0.248s

---

Today:

$ time ./wp.pugs.pl < /usr/src/linux/COPYING > foo

real    0m5.105s
user    0m4.898s
sys     0m0.096s

$ time ./wp.rakudo.pl < /usr/src/linux/COPYING > foo
Divide by zero
current instr.: '' pc -1 ((unknown file):-1)
Segmentation fault

real    0m3.236s
user    0m0.447s
sys     0m0.080s

Late additions: The crash has been dealt with at http://stackoverflow.com/questions/3144043. The Rakudo program is inefficient, see comments below and http://justrakudoit.wordpress.com/2010/06/30/rakudo-and-speed/.

Answer 4

Another thing you have to understand about the lack of optimization is that it's compounded. A large portion of Rakudo is written in Perl 6. So for example the [+] operator is implemented by the method Any.reduce (called with $expression set to &infix:<+>), which has as its inner loop

for @.list {
    @args.push($_);
    if (@args == $arity) {
        my $res = $expression.(@args[0], @args[1]);
        @args = ($res);
    }
}

in other words, a pure-perl implementation of reduce, which itself is being run by Rakudo. So not only is the code you can see not getting optimized, the code that you don't see that's making your code run is also not getting optimized. Even instances of the + operator are actually method calls, since although the + operator on Num is implemented by Parrot, there's nothing yet in Rakudo to recognize that you've got two Nums and optimize away the method call, so there's a full dynamic dispatch before Rakudo finds multi sub infix:<+>(Num $a, Num $b) and realizes that all it's really doing is an 'add' opcode. It's a reasonable excuse for being 100-1000x slower than Perl 5 :)

Update 8/23/2010

More information from Jonathan Worthington on the kinds of changes that need to happen with the Perl 6 object model (or at least Rakudo's conception of it) to make things fast while retaining Perl 6's "everything is method calls" nature.