sub query {
    $dbh->selectrow_array(q{ SELECT now() });
}

sub ping_and_query {
    $dbh->selectrow_array(q{ SELECT now() }) if $dbh->ping;
}

cmpthese(-2, {
    'query'      => \&query,
    'ping+query' => \&ping_and_query,
});

---
              Rate ping+query      query
ping+query  6349/s         --       -39%
query      10327/s        63%         --