Speed loss with parameters global_vars and loop_context_vars

I coded a site with an outer loop, an inner loop and an inner inner loop. global_vars and loop_context_vars were on.  
 
I was wondering about the time the output of this site lasts: 14 seconds ! After this I turned gobal_vars and loop_context_vars off and was wondering again: the output was processed after 1.5 seconds. 
 
I wrote a simplified Example (see below) and got the following results on my system: 
global_vars=1, loop_context_vars=1: 2.4 seconds 
global_vars=1, loop_context_vars=0: 5.7 seconds 
global_vars=0, loop_context_vars=1: 5.7 seconds 
global_vars=1, loop_context_vars=1: 13.0 seconds !!! 
 
So here is my question: Is this behavior normal ? 
 

Example: Please toggle the values of global_vars and loop_context_vars to see the difference. 


html_tmpl.pl--------------------------------------------- 
#!/usr/bin/perl -w 
 
use HTML::Template; 
use Time::HiRes qw(gettimeofday); 
 
my $inner_loop; 
for(my $i=0; $i<500; $i++) { 
  my $inner_inner_loop; 
  for(my $dat=1; $dat<=12; $dat++) { 
    push(@$inner_inner_loop, {'data' => $dat}); 
  } 
  push(@$inner_loop, { 'inner_inner_loop' => $inner_inner_loop }); 
} 
 
my $outer_loop; 
push(@$outer_loop, {'inner_loop' => $inner_loop}); 
 
my $tmpl = HTML::Template->new(filename=>'html_tmpl.tmpl', global_vars=>1, loop_context_vars=>0); 
$tmpl->param('outer_loop' => $outer_loop); 
 
my $t0 = gettimeofday; 
my $output = $tmpl->output(); 
my $t1 = gettimeofday; 
print $t1-$t0; 
------------------------------------------------------ 


html_tmpl.tmpl---------------------------------------- 
<tmpl_loop name="outer_loop"> 
  <tmpl_loop name="inner_loop"> 
    <tmpl_loop name="inner_inner_loop"> 
      <tmpl_var name="data">
    </tmpl_loop>
  </tmpl_loop> 
</tmpl_loop> 


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