change latency
$ out/opt/net/rpc/benchmark/benchmark_client --request_num=1000000 --thread_num=2
E1125 17:53:02.186866 20913 benchmark_client.cc:39] all completed
E1125 17:53:02.187244 20913 benchmark_client.cc:40] 2000000 completed in 4825 ms
 QPS: 414000