Add SMP Awareness to Thread Timeslicing

[Joel Sherrill]

On each clock tick, there is accounting which must be done for timeslicing. The time quantum for each executing thread must be decremented and, if the remaining time goes to zero, then the thread must logically perform a yield operation. The current implementation is in a method called _Thread_Tickle_timeslice. This only examines the thread currently executing on ONE CPU. In an SMP system, this management must be done for all of the threads across all CPUs.

This patch adds an "at tick" entry point to the scheduler plugin interface. This allows each scheduler implementation to perform whatever actions it needs to on each clock tick. The current schedulers are all priority based with timeslicing so the Deterministic Priority Scheduler and Simple Priority Scheduler can use the same "at tick" handler. The Simple SMP Priority Scheduler provides its own implementation.

It may be possible to refactor out a common "update timeslice info on thread" routine but, if possible, that will be a follow up action.

All non-SMP tests pass on SIS.

[Joel Sherrill]

First version for review

[Joel Sherrill]

2nd revision

[Joel Sherrill]

Committed.

[Gedare Bloom]

Replace Version=HEAD with Version=4.11 for the tickets with Milestone >= 4.11