Additional monitoring histograms for HLT online framework
Two main changes are made:
- Add monitoring histogram NoEventFraction which shows the fraction of getNext() calls returning the NO_EVENT status vs LB number. This value will be proportional to the farm busy percentage. 100% calls returning NO_EVENT = farm is idle, has no events to process. 0% calls returning NO_EVENT = farm is fully occupied.
- Add monitoring histogram SlotIdleTime showing the time between freeing a scheduler slot and allocating it again with another event. This time should be minimal to ensure efficient use of the scheduler thread pool.
And two minor changes:
- Improve how soft timeout value is stored: store std::chrono::duration directly instead of repeatedly casting from int.
- Adjust the unit and range of the TIME_getNext histogram