Compile-time difference

          Rate single double
single 30027/s     --    -0%
double 30160/s     0%     --

Run-time difference

            Rate single double
single 5968932/s     --   -13%
double 6893402/s    15%     --

            Rate double single
double 6218672/s     --   -12%
single 7062848/s    14%     --

##</code><code>##

use strict;
use warnings;

use Benchmark qw( cmpthese );

my $as = 'a' x 100;

sub c_dq {
  eval "\$a = \"$as\";";
}

sub c_sq {
  eval "\$a = '$as';";
}

eval "sub r_dq { \$a = \"$as\"; }";

eval "sub r_sq { \$a = '$as'; }";

print("Compile-time difference\n");

cmpthese(-3, {
   double => \&c_dq,
   single => \&c_sq,
});

print("Run-time difference\n");

cmpthese(-3, {
   double => \&r_dq,
   single => \&r_sq,
});