For that input, split is the fastest for me. 
           Rate    regex unpack_C unpack_a    split
regex    9.95/s       --      -2%     -46%     -50%
unpack_C 10.1/s       2%       --     -45%     -49%
unpack_a 18.3/s      84%      80%       --      -9%
split    20.0/s     101%      97%       9%       --

[download]
use strict;
use warnings;

use Benchmark qw( cmpthese );

my %tests = (
   split    => q{ my @a = split //, $buf;             },
   regex    => q{ my @a = $buf =~ /./sg;              },
   unpack_C => q{ my @a = map chr, unpack 'C*', $buf; },
   unpack_a => q{ my @a = unpack '(a)*', $buf;        },
);

$_ = "use strict; use warnings; our \$buf; $_ 1"
   for values(%tests);

local our $buf = "abcdef\x00ghik" x 10_000;
cmpthese(-2, \%tests);

[download]

Update: Changed (A)* to (a)* in response to BrowserUk's reply.

In reply to Re: Convert string to array - performance challenge by ikegami
in thread Convert string to array - performance challenge by rtillian

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