use Benchmark qw(cmpthese);

our $t_count = 3;
our %hosts  = map { $_ => $t_count - ( rand 50 > 49 ? 1 : 0 ) } (1 .. 1000);

my $count = 10000;
cmpthese($count, {
  do    => 'my %t = %main::hosts; do { delete $t{$_} unless $t{$_} == $main::t_count } for keys %t;',
  map   => 'my %t = %main::hosts; map { delete $t{$_} unless $t{$_} == $main::t_count } keys %t;',
  or    => 'my %t = %main::hosts; $t{$_} == $main::t_count or delete $t{$_} for keys %t;',
  slice => 'my %t = %main::hosts; delete @t{ grep { $t{$_} != $main::t_count } keys %t };',
  copy  => 'my %t = %main::hosts; %t = map { $t{$_} == $main::t_count ? ($_, $t{$_}) : ()} keys %t;',
  nada  => 'my %t = %main::hosts;'
});

##</code><code>##

        Rate  copy   map    or    do slice  nada
copy  1372/s    --  -57%  -57%  -57%  -58%  -78%
map   3175/s  131%    --   -2%   -2%   -2%  -50%
or    3226/s  135%    2%    --    0%   -0%  -49%
do    3226/s  135%    2%    0%    --   -0%  -49%
slice 3236/s  136%    2%    0%    0%    --  -49%
nada  6289/s  358%   98%   95%   95%   94%    --