workflow parallel and number of executers

[EK]

Hi , 

  I am trying to move from build flow to workflow , but I am facing many issues in which some i have managed to overcome but now I am facing the following:

while using build flow when running sub jobs in parallel they all where invoked in same executer on the master , but when I try to do the same in workflow each sub job needs its own executer of the master - and I find myself stuck as some are waiting for next available executer, 

I need help to know how I can invoke sub jobs in parallel while using same executer of the master ?  

Best Regards

[EK]

I think I have managed , but the documentation is diffidently not that clear and does not help . 

in my sub workflow script\job - I do only limited stuff surrounded by node('master') closer -- this way the executer is released very quickly -->  in my case its just load of external groovy script - that has a common code and wrapper code for invoking jobs - (this is the reason for moving to workflow).

that way the sub workflow script does not consume all available executers of the master and they run really in parallel without the need to wait for next free executer. 
The only limitation(difference with build flow)  I see now is that the sub workflow job is not being running under the same executer( or any other executer of the master) --> but this I think I can ignore.