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Quasi static scheduler runtime #90

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Quasi static scheduler runtime #90

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@lsk567 lsk567 commented Jun 28, 2022 •
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This is a draft PR for the C runtime of the quasi-static (QS) scheduler. The design of the scheduler follows the one in this report and (mostly) in this discussion thread.

This scheduler runtime concurrently must be compiled against a schedule.h file, which should be generated by a static schedule generator in lfc. A preliminary version of the schedule generator is implemented using Uclid5 on this branch.

Here are the outstanding TODOs in order to make this scheduler able to be merged in:

  • Support an instruction file specified on the command line. The scheduler then reads the instructions line-by-line from the file during execution. This feature could support scheduler development.

An important TODO after a more efficient schedule generator is merged into lingua-franca:

  • Adding QS tests in the regression test suite.

More research-related items:

  • Debug the performance issue of this scheduler when running benchmarks, which is significantly slower than the default NP scheduler.
  • Support the branch instruction in the instruction set.
  • Implement working-stealing on top of QS.
  • Take WCET into account when generating schedules.
  • Support LET scheduling.
  • Establish an understandable mapping between reactions and reaction IDs (currently no clear mapping).
  • A validator tool that ensures dependency constraints are satisfied in a schedule file.
  • (Peter) Explore branch prediction in modern processors.

Use cases:

  1. Deliver better performance for certain programs (TODO: identify this subset of programs);
  2. Help real-time systems people develop new schedulers;
  3. More deterministic execution;
  4. In formal verification, can provide stronger axioms (LF semantics + QS scheduler semantics) and enable timing analysis given WCETs.

@lsk567 lsk567 self-assigned this Jun 28, 2022
@lsk567 lsk567 requested a review from Soroosh129 June 28, 2022 23:01
edwardalee
edwardalee reviewed Jun 29, 2022
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Looks promising. A few questions included. Also, there is not enough documentation to know how to use it. Ideally, it would explain how to create (manually) a quasi-static schedule somewhere so that one could use these extensions.

core/threaded/scheduler_QS.c Outdated Show resolved Hide resolved
core/threaded/scheduler_QS.c Show resolved Hide resolved
core/threaded/scheduler_QS.c Outdated Show resolved Hide resolved
core/threaded/scheduler_QS.c
// lf_mutex_lock(&_lf_sched_instance->_lf_sched_semaphore->mutex);
// lf_cond_wait(&_lf_sched_instance->_lf_sched_semaphore->cond, &_lf_sched_instance->_lf_sched_semaphore->mutex);
// lf_mutex_unlock(&_lf_sched_instance->_lf_sched_semaphore->mutex);
lf_cond_wait(&_lf_sched_instance->_lf_sched_array_of_conds[0], &mutex);
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Should this index be the worker number rather than 0?

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Although the field is called _lf_sched_array_of_conds, the current implementation only uses one condition variable to coordinate time advancement. An array is used here so that a future scheduler implementation that needs multiple condition variables can still use this field.

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A comment in the code about this would be helpful.

core/threaded/scheduler_QS.c Show resolved Hide resolved
core/threaded/scheduler_instance.h Outdated Show resolved Hide resolved
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@lsk567 lsk567 force-pushed the quasi-static-scheduler branch from 0bfa648 to c811341 Compare September 7, 2022 00:50
@lsk567 lsk567 changed the title [Draft] Quasi static scheduler runtime Quasi static scheduler runtime Sep 13, 2022
@lsk567 lsk567 marked this pull request as ready for review September 13, 2022 22:45
@lsk567 lsk567 requested a review from lhstrh September 13, 2022 23:05
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lhstrh commented Oct 31, 2023

What is the relationship between this PR and #241?

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