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Postings from November 2009
Oops, forgot to put the function in.
karl williamson wrote:
> Nicholas Clark wrote:
>>> [...]
>>
>> Also, you mentioned Encode and the files it generated. I found a lot
>> of scope
>> for optimisation within enc2xs, which dramatically decreased its
>> memory use
>> and run time, without needing large fundamental design changes to how it
>> worked. And I managed that with only Devel::DProf. I'm curious what
>> can be
>> achieved with Devel::NYTProf on mktables. (Which is a task that is within
>> the skill set of any of the 600 subscribers to this list. I'm hoping
>> that it
>> might appeal to at least one.)
>
> So, I tried it with NYTProf. As I expected (I had used DProf earlier),
> the highest usage subroutine was my pure Perl version of
> Scalar::Util::refaddr, reproduced below. A third of the total time was
> spent in this routine. (This is required because miniperl doesn't do
> dynamic loading, so refaddr is not available.)
>
> When I was writing mktables, I was under the impression that refaddr
> would be brought into the core for 5.12. There was an agreement to that
> effect, but I guess no one ever got around to actually doing it.
>
> When I run this under perl instead of miniperl, and change objaddr to
> just return refaddr, the combination still takes quite a lot of time. If
> refaddr were in the core would it be in-lined?
>
> I found a few surprises; I haven't pored over the results, though. One
> is that I left in a trace statement that got to the trace subroutine
> before discovering that it had nothing to do. This added not very much
> time.
>
> Based on looking at existing code in utf8_heavy.pl, I had presumed that
> the Perl optimizer would remove code that depended on a constant
> subroutine that returns false. That is, 'foo if DEBUG' would be
> optimized away if there was a line: 'sub Debug { 0 }' But that appears
> to not be the case.
>
> There were more string evals than I expected, though the total time did
> not add up to all that much. I couldn't find a way in NYTProf to
> highlight those.
>
> There are two columns in the nytprofhtml output for subroutines that I
> can't figure out what they mean, and saw no documentation for, 'P' and 'F'.
>
> I also did not see anything there for memory usage. I don't know how
> Perl handles using up too much memory. The old mktables kept all its
> tables in memory, and so I felt free to do so as well. But the new
> mktables handles quite a few more tables than the old one. I would
> think you would get thrashing if the memory usage got too big. I wonder
> if Steve's machine doesn't have much memory. When I run mktables using
> perl instead of miniperl, I get execution times between 30 and 40 seconds.
>
sub objaddr($) {
# Returns the address of the blessed input object. Uses the XS
version if
# available. It doesn't check for blessedness because that would do a
# string eval every call, and the program is structured so that this is
# never called for a non-blessed object.
return Scalar::Util::refaddr($_[0]) if $has_fast_scalar_util;
# Get the package
my $pkg = ref($_[0]) or return undef;
# Change to a fake package to defeat any overloading
bless $_[0], 'main::Fake';
# Numifying a ref gives its address.
my $addr = 0 + $_[0];
# Return to original class
bless $_[0], $pkg;
return $addr;
}
I found that any overload in a class caused the numifying to fail if I
did it in that class; hence the blesses are necessary.
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