tracking: SMP Support

[elenaf9]

Summary

Add support for symmetric multiprocessing (SMP), i.e. platforms with multiple symmetric cores.
An example for such a platform is the Raspberry RP2040, with Dual ARM Cortex-M0+ cores.

Subtasks for basic a implementation

A first implementation for the RP2040 is drafted in #241. There is quite a lot still missing there.
The below list includes some central tasks, but will grow while I am working on this.

• riot-rs-runqueue: support multiple currently running threads #244
• Multicore support in the scheduler: feat(threads): multicore support  #397
  • Schedule n highest-priority threads on the n cores
  • Trigger scheduler of other cores
  • Idle thread for each core
  • Affinity Masks
  • Optimize scheduler invocations to reduce context switches and priority inversion
  • Supported chips:
    • RP2040
    • ESP32S3
• Optimize locking primitives (spinlocks for shared resources, scheduler lock, ...)
  • Test different levels of locking (fine-grained vs one global lock)
  • Use independent internal critical section

Additional features (to be discussed):

• Priority inheritance (for threads holding a shared resource). Started in feat(threads): add mutex with priority inheritance #398. (Is this orthogonal?)

Benchmarks

The implementation should be tested with benchmarks to compare the performance with the single-core version.
Off the top of my head, some interesting metrics would be:

• Response time
• Makespan
• Priority inversions
• ...

Edit: a set of benchmarks is currently implemented outside of this repo: elenaf9/RIOT-rs-application. Selected benchmarks will be moved in this repo eventually).

[kaspar030]

I consider this done, #398 is orthogonal.