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Postings from November 2009
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.
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