Re: Re(2): updating an array of strings

Perl never ceases to amaze me. After seeing Arien's point I wondered just how much slower it was to build a stack frame, do the assignment and knock the stack frame down again.

I've seen various references to "the overhead of calling a sub" and have been guilty of not sub-ing when I should have because of it. I needn't have worried. I was expecting a vastly higher overhead than this demonstrates!

#!perl -w
use strict;
use Benchmark;

my @ary = 0 .. 100;

Benchmark::cmpthese ( 10_000_000, {
        'assignment'    => '$ary[1] = -1;',
        'splice'         => 'splice @ary, 1, 1, -1;'
    }
);
__END__
# Output
C:\test>192779
Benchmark: timing 10000000 iterations of assignment, splice...
assignment: 21 wallclock secs (19.65 usr +  0.00 sys = 19.65 CPU) @ 50
+8931.75/s (n=10000000)
    splice: 56 wallclock secs (57.13 usr +  0.01 sys = 57.14 CPU) @ 17
+4999.56/s (n=10000000)
               Rate     splice assignment
splice     175000/s         --       -66%
assignment 508932/s       191%         --
[download]

What's this about a "crooked mitre"? I'm good at woodwork!

Comment on Re: Re(2): updating an array of strings Download Code

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Re: Re: Re(2): updating an array of strings by theorbtwo (Prior) on Aug 26, 2002 at 10:39 UTC
Umm, neither of these calls a subroutine. splice is a list operator, not a sub -- no call stack need be generated, because no perl code is being called. `#!perl -w use strict; use Benchmark; my @ary = 0 .. 100; sub test { $a++; } Benchmark::cmpthese ( -1, { direct => sub {$a++}, sub => sub {test} } ); __END__ Benchmark: running direct, sub, each for at least 1 CPU seconds... direct: 1 wallclock secs ( 1.48 usr + 0.00 sys = 1.48 CPU) @ 34 +6460.81/s (n=512762) sub: 1 wallclock secs ( 1.00 usr + 0.00 sys = 1.00 CPU) @ 13 +7843.00/s (n=137843) Rate sub direct sub 137843/s -- -60% direct 346461/s 151% --` [download] Confession: It does an Immortal Body good.	[reply] [d/l]

Replies are listed 'Best First'.

Re: Re: Re(2): updating an array of strings
by theorbtwo (Prior) on Aug 26, 2002 at 10:39 UTC

Umm, neither of these calls a subroutine. splice is a list operator, not a sub -- no call stack need be generated, because no perl code is being called.

#!perl -w
use strict;
use Benchmark;

my @ary = 0 .. 100;

sub test {
 $a++;
}

Benchmark::cmpthese ( -1, {
    direct => sub {$a++},
    sub    => sub {test}
   }
);
__END__
Benchmark: running direct, sub, each for at least 1 CPU seconds...
    direct:  1 wallclock secs ( 1.48 usr +  0.00 sys =  1.48 CPU) @ 34
+6460.81/s (n=512762)
       sub:  1 wallclock secs ( 1.00 usr +  0.00 sys =  1.00 CPU) @ 13
+7843.00/s (n=137843)
           Rate    sub direct
sub    137843/s     --   -60%
direct 346461/s   151%     --
[download]

Confession: It does an Immortal Body good.

[reply]
[d/l]