On Mon, 19 Mar 2001, Paul wrote:
>
> --- Geoffrey Young <[EMAIL PROTECTED]> wrote:
> > mod_perl digest
> > March 11, 2001 - March 17, 2001
> > Recent happenings in the mod_perl world...
> > . . .
> > mailing list highlights
> > . . .
> > o There was an OT but interesting thread on whether lexical
> > variables are faster than global variables [10]. This
> > response in particular may be of interest to those who
> > want to know more about perlguts [11]
>
> As one more installment on that thread, I got an email using Benchmark
> to test it. It had the my() inside the test function, which was slower
> than package globals, but I moved it out and it was faster.
>
> Here's the test synopsis:
> ===========================
> C:\users\default>type tmp.pl
> use Benchmark;
> my $o; # packagewide deep-bound my() var
> sub outMY{
> $o = 0; # packagewide deep-bound my() var
> $o++ while ($o < 1000);
> };
> sub inMY{
> my $i = 0; # function-internal my() var
> $i++ while ($i < 1000);
> };
> sub gPK{
> $g = 0; # package global var
> $g++ while ($g < 1000);
> };
> timethese(5000, { 'External' => \&outMY,
> 'Internal' => \&inMY,
> 'Global' => \&gPK } );
>
> C:\users\default>perl -w tmp.pl
> Benchmark: timing 5000 iterations of External, Global, Internal...
> External: 5 wallclock secs ( 4.96 usr + 0.00 sys = 4.96 CPU)
> Global: 5 wallclock secs ( 5.01 usr + 0.00 sys = 5.01 CPU)
> Internal: 4 wallclock secs ( 5.07 usr + 0.00 sys = 5.07 CPU)
>
> ===================================================================
> Notice that a deep-bound my() variable was fastest, while a re-scoped
> my() was slowest, the package global being pretty close to halfway
> between in actual CPU usage.
>
> Hope that's useful to somebody. =o)
Unfortunately it's not very useful when the results are so close, unless
you specify the platform, compiler args, which malloc version was used and
much more. And others use the same or a similar setup.
I've run the same benchmark on linux(k2.2.17), perl 5.6.1-PATCH2 and there
are all the other details that I'm not telling here. But just to make a
point, I get results with 'global' always being faster and
external/internal giving relatively inconsistent results (see the
variations on CPU cycles). For example, your code executed four times:
Benchmark: timing 5000 iterations of External, Global, Internal...
External: 6 wallclock secs ( 5.57 usr + 0.64 sys = 6.21 CPU) @
Global: 6 wallclock secs ( 5.14 usr + 0.60 sys = 5.74 CPU) @
Internal: 7 wallclock secs ( 5.57 usr + 0.52 sys = 6.09 CPU) @
Benchmark: timing 5000 iterations of External, Global, Internal...
External: 7 wallclock secs ( 5.52 usr + 0.63 sys = 6.15 CPU) @
Global: 5 wallclock secs ( 5.01 usr + 0.44 sys = 5.45 CPU) @
Internal: 6 wallclock secs ( 5.45 usr + 0.62 sys = 6.07 CPU) @
Benchmark: timing 5000 iterations of External, Global, Internal...
External: 7 wallclock secs ( 5.54 usr + 0.56 sys = 6.10 CPU) @
Global: 5 wallclock secs ( 5.08 usr + 0.43 sys = 5.51 CPU) @
Internal: 7 wallclock secs ( 5.55 usr + 0.79 sys = 6.34 CPU) @
Benchmark: timing 5000 iterations of External, Global, Internal...
External: 6 wallclock secs ( 5.65 usr + 0.53 sys = 6.18 CPU) @
Global: 6 wallclock secs ( 5.18 usr + 0.50 sys = 5.68 CPU) @
Internal: 7 wallclock secs ( 5.56 usr + 0.46 sys = 6.02 CPU) @
As you can see on my setup, Global is the fastest, and Internal comes next
in 3 out of 4 cases... Also I've the -DDEBUGGIN on, so may be that's what
makes the difference. So the standard 5.6.0 without debugging enabled
gives inconsistent results as well:
Benchmark: timing 5000 iterations of External, Global, Internal...
External: 4 wallclock secs ( 3.13 usr + 0.54 sys = 3.67 CPU) @
Global: 4 wallclock secs ( 3.21 usr + 0.28 sys = 3.49 CPU) @
Internal: 3 wallclock secs ( 3.15 usr + 0.44 sys = 3.59 CPU) @
Benchmark: timing 5000 iterations of External, Global, Internal...
External: 4 wallclock secs ( 3.09 usr + 0.15 sys = 3.24 CPU) @
Global: 3 wallclock secs ( 3.19 usr + 0.51 sys = 3.70 CPU) @
Internal: 3 wallclock secs ( 3.17 usr + 0.26 sys = 3.43 CPU) @
Benchmark: timing 5000 iterations of External, Global, Internal...
External: 4 wallclock secs ( 3.10 usr + 0.35 sys = 3.45 CPU) @
Global: 4 wallclock secs ( 3.23 usr + 0.33 sys = 3.56 CPU) @
Internal: 4 wallclock secs ( 3.11 usr + 0.41 sys = 3.52 CPU) @
Benchmark: timing 5000 iterations of External, Global, Internal...
External: 4 wallclock secs ( 3.17 usr + 0.29 sys = 3.46 CPU) @
Global: 3 wallclock secs ( 3.15 usr + 0.38 sys = 3.53 CPU) @
Internal: 4 wallclock secs ( 3.16 usr + 0.39 sys = 3.55 CPU) @
which gives no clue at all, which is the faster method to use. Though it's
almost twice faster with having -DDEBUGING off... :)
_____________________________________________________________________
Stas Bekman JAm_pH -- Just Another mod_perl Hacker
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