[WorkloadConfigurator] Add support for specifying number of drivers and workers-per-driver (extension to #86)

[tsg-]

Workload configurator currently supports specifying only the total number of workers for a stage .. it will be useful to specify the load as:

1. "workers=" spec: total number of workers (number of drivers defaults to that specified in controller.ini, with workers-per-driver being symmetrically divided between drivers)
2. "drivers=" and "workers=" spec: total number of drivers and total number of workers. (number of drivers ) <= (number of drivers configured in controller.ini). Worker specification used to determine workers-per-driver (symmetric division).
3. "drivers=" and "workers_per_driver=" spec: total number of drivers and workers-per-driver. (number of drivers ) <= (number of drivers configured in controller.ini). Total number of workers is redundant spec in this case (ignored).

Again, if all of "drivers=", "workers_per_driver=" and "workers=" is specified, the "workers=" spec is ignored. The total number of workers is instead calculated as in (3).

[ywang19]

There is one attribute named "driver" which is originally used to assign the work to specific driver, which should cover the spec you mentioned. one minor concern is it's a bit long to validate it last time.

[ywang19]

will verify to decide if needs enhancement.

[tsg-]

(3) above is not supported. There was a desire to be able to configure "workers_per_driver" in addition to case (2) where the number of workers is being divided among drivers equally. An example use case would be where I've configured say 4 drivers, but I want to use only 2 and force higher number of threads each, and be able to do that without (COSbench config change + restart) and per workload. Thoughts?

[ywang19]

Need more time to understand the those scenarios, target to support in v0.4.1.