Currently the Java and C++ versions of the QPS Client allow one to perform a fixed number of calls. When using them for benchmarking I think it would make much more sense if we could tell the client to hit the server for some period of time (i.e. 30 minutes) i.e. 1 million calls just mean something completely different on GCE, Prod and your local workstation.

WDYT @vjpai . If you agree, I could also come up with a PR for the C++ version.