A Timely Start
by Jean-Louis Leroy
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Pages: 1, 2, 3
Why Was Perl Slower?
In my case, though, the sad truth was that the Perl version of the FTP script spent 95 percent of its time getting started; the meat of the script, the code written by my colleague, accounted for only five percent of the execution time. The ksh version, on the other hand, started to work on the job nearly immediately.
My lightning talk ended with the conclusion that Perl needs a compiler--badly. In the final slides I addressed some popular objections against this statement, the more important one being that "it won't make your code run faster." I know: I want it to start faster.
Several hackers came for a discussion after my talk. Some of their objections were interesting but missed the point. ("The total execution time is good enough." Me: "It's not up to me to decide, there are specs; and the FTP version is five times faster. That's what I'm talking about.")
However, other remarks suggested that some stones remained unturned. One of the attendants timed perl -MNet::FTP -e 0 under my eyes and indeed it loaded quite fast on his laptop. It loaded faster than on the Agency's multi-CPU, 25000-euro computers. How come?
The answer turned out to be the length of PERL5LIB. The Agency has collections of systems that build upon one another. Each system may contain one or several directories hosting Perl modules. The build system produces a value for PERL5LIB that includes the Perl module directories for the system, followed by the module directories of all of the systems it builds upon, recursively.
I wrote a small module, Devel::Dependencies, which uses BEGIN and CHECK blocks to find all of the modules that a Perl program loads. Optionally, it lists the path to each module, the position of that path within @INC, and the sum of all of the positions at the end. This gives a good idea of the number of directory searches Perl has to perform when loading modules.
I used it on a one-line script that just says use Net::FTP. Here's the result:
$ echo $PERL5LIB
XxB:
/build/MAP/CONFIG!11.213/idl/stubs:
/build/MAP/CONFIG!11.213/perl/lib:
/build/MAP/CONFIG!11.213/pm:
/build/LIB/UTILS!11.151/ftpstuff:
/build/LIB/UTILS!11.151/alien/PA-RISC2.0:
/build/LIB/UTILS!11.151/alien:
/build/LIB/UTILS!11.151/perl/lib:
/build/LIB/UTILS!11.151/pm:
/build/MAP/MAP_SERVER!11.197/pm:
/build/CONTROL/KLIBS!11.132/idl/stubs:
/build/CONTROL/KLIBS!11.132/perl/lib:
/build/CONTROL/KLIBS!11.132/pm:
/build/CONTROL/ACME!11.177/idl/stubs:
/build/CONTROL/ACME!11.177/pm:
/build/CONTROL/ADAPTER!11.189/pm:
/build/MAP/HMI!1.12.165/idl/stubs:
/build/CONTROL/KERNEL_INIT!11.130/pm:
/build/CONTROL/BUSINESS!11.176/pm:
/build/CONTROL/KERNEL!11.130/pm:
/build/BASIC/SSC!11.78/pm:
/build/BASIC/LOG!11.78/perl/lib:
/build/BASIC/LOG!11.78/pm:
/build/BASIC/BSC!11.77/pm:
/build/BASIC/POLYORB!11.39/idl/stubs:
/build/BASIC/TEST!11.58/perl/lib/ldap/interface:
/build/BASIC/TEST!11.58/perl/lib/ldap:
/build/BASIC/TEST!11.58/perl/lib:
/build/BASIC/TEST!11.58/pm:
/build/BASIC/TANGRAM!11.53/perl/lib:
/build/BASIC/TANGRAM!11.53/pm:
/build/LIB/PERL!5.6.1.1.39/lib/site_perl:
/build/LIB/PERL!5.6.1.1.39/lib:
/build/LIB/PERL!5.6.1.1.39/alien:
/build/LIB/PERL!5.6.1.1.39/pm:
/build/LIB/GNU!11.30/pm:
/build/CM/LIB!2.1.221/perl/lib/wle/interface:
/build/CM/LIB!2.1.221/perl/lib:
/build/CM/LIB!2.1.221/alien:
/build/CM/LIB!2.1.221/pm:
/build/CM/CM_LIB!2.1.96/perl/lib/MakeCfg:
/build/CM/CM_LIB!2.1.96/perl/lib:
/build/CM/CM_LIB!2.1.96/pm:
/build/CM/EXT_LIBS!2.1.6/perl/lib:
/build/CM/EXT_LIBS!2.1.6/alien:
/build/CM/EXT_LIBS!2.1.6/pm:
XxE
$ perl -c -MDevel::Dependencies=origin ftp.pl
Devel::Dependencies 23 dependencies:
/build/LIB/UTILS!11.151/ftpstuff/Net/libnet.cfg /build/LIB/UTILS!11.151/ftpstuff/Net/libnet.cfg (6)
Carp.pm /build/LIB/PERL!5.6.1.1.39/lib/Carp.pm (38)
Config.pm /build/LIB/PERL!5.6.1.1.39/lib/PA-RISC2.0/Config.pm (37)
Errno.pm /build/LIB/PERL!5.6.1.1.39/lib/PA-RISC2.0/Errno.pm (37)
Exporter.pm /build/LIB/PERL!5.6.1.1.39/lib/Exporter.pm (38)
Exporter/Heavy.pm /build/LIB/PERL!5.6.1.1.39/lib/Exporter/Heavy.pm (38)
IO.pm /build/LIB/PERL!5.6.1.1.39/lib/PA-RISC2.0/IO.pm (37)
IO/Handle.pm /build/LIB/PERL!5.6.1.1.39/lib/PA-RISC2.0/IO/Handle.pm (37)
IO/Socket.pm /build/LIB/PERL!5.6.1.1.39/lib/PA-RISC2.0/IO/Socket.pm (37)
IO/Socket/INET.pm /build/LIB/PERL!5.6.1.1.39/lib/IO/Socket/INET.pm (38)
IO/Socket/UNIX.pm /build/LIB/PERL!5.6.1.1.39/lib/IO/Socket/UNIX.pm (38)
Net/Cmd.pm /build/LIB/UTILS!11.151/ftpstuff/Net/Cmd.pm (6)
Net/Config.pm /build/LIB/UTILS!11.151/ftpstuff/Net/Config.pm (6)
Net/FTP.pm /build/LIB/UTILS!11.151/ftpstuff/Net/FTP.pm (6)
SelectSaver.pm /build/LIB/PERL!5.6.1.1.39/lib/SelectSaver.pm (38)
Socket.pm /build/LIB/PERL!5.6.1.1.39/lib/PA-RISC2.0/Socket.pm (37)
Symbol.pm /build/LIB/PERL!5.6.1.1.39/lib/Symbol.pm (38)
Time/Local.pm /build/LIB/PERL!5.6.1.1.39/lib/Time/Local.pm (38)
XSLoader.pm /build/LIB/PERL!5.6.1.1.39/lib/PA-RISC2.0/XSLoader.pm (37)
strict.pm /build/LIB/PERL!5.6.1.1.39/lib/strict.pm (38)
vars.pm /build/LIB/PERL!5.6.1.1.39/lib/vars.pm (38)
warnings.pm /build/LIB/PERL!5.6.1.1.39/lib/warnings.pm (38)
warnings/register.pm /build/LIB/PERL!5.6.1.1.39/lib/warnings/register.pm (38)
Total directory searches: 739
ftp.pl syntax OKNow it looked like I had found the wasted time.
