You can even squeeze a little more out. This is ~5% faster on my system.

    my($buf, $chunk, @lines);    
    while(read FILE, $buf, BUFFER_SIZE) {
        $chunk .= $buf;
        @lines = split /\n/, $chunk;
        $chunk = chomp $buf ? '' : pop @lines;

        foreach (@lines) {}
    }
[download]

(BUFFER_SIZE is just a constant I was using)