You will need to use Time::HiRes to get a fine enough time granularity to do anything useful.
I while back a wrote a small script to monitor my servers for performance changes (so that I had ammo when complaining to my DSL provider). I found that the size of the page you are downloading effect the time significantly since there are fixed costs to the socket connection. Therefore I used a lower level module Net::HTTP so that I could specify a fixed download size. Here is the code snippet...
use Time::HiRes qw(gettimeofday);
:
:
my $prep_start = gettimeofday ;
$conn = new Net::HTTP( 'Host'=>"$url") || goto END_LOOP;
my $prep_end = gettimeofday;
# - - - - - Start - - - - - -
my $start = gettimeofday ;
$rtn = $conn->write_request(GET => "/", 'User-Agent' => "perlworks/1.
+0") || goto END_LOOP;;
my ($code, $mess, %h) = $conn->read_response_headers();
$data{'page_size'} = $conn->read_entity_body($page, 512);
my $end = gettimeofday;
# - - - - - Stop - - - - - -
:
:
my $delta = $end - $start;