What is the different performance on select and epoll : latency and throughput?

what is the different performance on select and epoll : latency and throughput?
any test report on latency and throughput when connect with select and epoll?

when we client test on large cluster couchbase in select mode, we meet high latency and low throughput which 30 servers less than 1 servers, both on read and write; we have tried on small cluster like 8, it works well;
but not yet test on epoll(libevent) mode actually we are working on it, anybody think it is select/epoll related?