You can find below some of the "hidden" options of p2. These options are most of the time controlled through system properties and are not API. As such we reserve the right to change those at any time.
eclipse.p2.max.threads to control the number of active thread. The default is 4. eclipse.p2.force.threading to enable or disable the multi threaded download. The default is true. eclipse.p2.mirrors to disable the usage of mirrors when downloading artifacts. The default is true.