C:\test>junk -B=4 < 1gb.dat
Found 6559 matches in 10.778 seconds using 4 kb reads

C:\test>junk -B=64 < 1gb.dat
Found 6559 matches in 10.567 seconds using 64 kb reads

C:\test>junk -B=256 < 1gb.dat
Found 6559 matches in 10.574 seconds using 256 kb reads

C:\test>junk -B=1024 < 1gb.dat
Found 6559 matches in 10.938 seconds using 1024 kb reads

C:\test>junk -B=4096 < 1gb.dat
Found 6559 matches in 10.995 seconds using 4096 kb reads

C:\test>junk -B=65536 < 1gb.dat
Found 6559 matches in 12.533 seconds using 65536 kb reads

##</code><code>##

#! perl -slw
use strict;
use Time::HiRes qw[ time ];

our $B //= 64;
$/ = \( $B *1024 );

binmode STDIN, ':raw:perlio';

my $start = time;
my $count = 0;
while( <STDIN> ) {
   ++$count while m[123]g;
}
printf "Found %d matches in %.3f seconds using %d kb reads\n",
    $count, time()-$start, $B;