Library prosa.analysis.facts.preemption.task.limited

Require Export prosa.analysis.facts.preemption.job.limited.
Require Export prosa.model.task.preemption.limited_preemptive.

Platform for Models with Limited Preemptions

In this section, we prove that instantiation of functions job_preemptable and task_preemption_points to the limited preemptions model indeed defines a valid preemption model with bounded non-preemptive regions.
Section LimitedPreemptionsModel.

Consider any type of tasks ...
  Context {Task : TaskType}.
  Context `{TaskCost Task}.

... and any type of jobs associated with these tasks.
  Context {Job : JobType}.
  Context `{JobTask Job Task}.
  Context `{JobArrival Job}.
  Context `{JobCost Job}.

We assume that jobs are preemptable only at specific points during their execution, ...
  Context `{JobPreemptionPoints Job}.
  Context `{TaskPreemptionPoints Task}.
... i.e., we assume limited-preemptive jobs.
  #[local] Existing Instance limited_preemptive_job_model.

Consider any arrival sequence.
  Variable arr_seq : arrival_sequence Job.

Next, consider any preemption-aware schedule of this arrival sequence...
  Context {PState : ProcessorState Job}.
  Variable sched : schedule PState.
  Hypothesis H_schedule_respects_preemption_model:
    schedule_respects_preemption_model arr_seq sched.

... where jobs do not execute before their arrival or after completion.
  Hypothesis H_jobs_must_arrive_to_execute : jobs_must_arrive_to_execute sched.
  Hypothesis H_completed_jobs_dont_execute : completed_jobs_dont_execute sched.

Consider an arbitrary task set ts.
  Variable ts : list Task.

Next, we assume that preemption points are defined by the model with fixed preemption points.
  Hypothesis H_valid_fixed_preemption_points_model:
    valid_fixed_preemption_points_model arr_seq ts.

Then we prove that functions job_preemptable and task_preemption_points define a model with bounded non-preemptive regions.
  Lemma fixed_preemption_points_model_is_model_with_bounded_nonpreemptive_regions:
    model_with_bounded_nonpreemptive_segments arr_seq .
  Proof.
    intros j ARR.
    move: H_valid_fixed_preemption_points_model ⇒ [LIM FIX].
    move: (LIM) ⇒ [BEG [END NDEC]]; move: (FIX) ⇒ [A1 [A2 [A3 [A4 A5]]]].
    case: (posnP (job_cost j)) ⇒ [ZERO|POS].
    - split.
      + rewrite /job_respects_max_nonpreemptive_segment /job_max_nonpreemptive_segment
              /lengths_of_segments /job_preemption_points; rewrite ZERO; simpl.
        by rewrite /job_preemptable /limited_preemptive_job_model; erewrite zero_in_preemption_points; eauto 2.
      + move ⇒ progr; rewrite ZERO leqn0; move ⇒ /andP [_ /eqP LE].
        ∃ 0; rewrite LE; split; first by apply/andP; split.
          by eapply zero_in_preemption_points; eauto 2.
    - split; last (move ⇒ progr /andP [_ LE]; destruct (progr \in job_preemptive_points j) eqn:NotIN).
      + rewrite /job_respects_max_nonpreemptive_segment
                /job_max_nonpreemptive_segment /lengths_of_segments; erewrite job_parameters_max_np_to_job_limited; eauto.
          by apply max_of_dominating_seq; intros; apply A5.
      + by ∃ progr; split; first apply/andP; first split; rewrite ?leq_addr.
      + move: NotIN ⇒ /eqP; rewrite eqbF_neg; move ⇒ NotIN.
        edestruct (work_belongs_to_some_nonpreemptive_segment arr_seq) as [x [SIZE2 N]]; eauto 2. move: N ⇒ /andP [N1 N2].
        set ptl := nth 0 (job_preemptive_points j) x.
        set ptr := nth 0 (job_preemptive_points j) x.+1.
        ∃ ptr; split; first last.
        × by unfold job_preemptable, limited_preemptive_job_model; apply mem_nth.
        × apply/andP; split; first by apply ltnW.
          apply leq_trans with (ptl + (job_max_nonpreemptive_segment j - ε) + 1); first last.
          -- rewrite addn1 ltn_add2r; apply N1.
          -- unfold job_max_nonpreemptive_segment.
             rewrite -addnA -leq_subLR -(leq_add2r 1).
             rewrite [in X in _ ≤ X]addnC -leq_subLR.
             rewrite !subn1 !addn1 prednK.
             { rewrite -[_.+1.-1]pred_Sn. rewrite /lengths_of_segments.
               erewrite job_parameters_max_np_to_job_limited; eauto.
                 by apply distance_between_neighboring_elements_le_max_distance_in_seq. }
             { rewrite /lengths_of_segments; erewrite job_parameters_max_np_to_job_limited; eauto.
               apply max_distance_in_nontrivial_seq_is_positive; first by eauto 2.
               ∃ 0, (job_cost j); repeat split.
               - by eapply zero_in_preemption_points; eauto.
               - by eapply job_cost_in_nonpreemptive_points; eauto.
               - by apply/eqP; rewrite eq_sym -lt0n; apply POS.
             }
  Qed.

Which together with lemma valid_fixed_preemption_points_model gives us the fact that functions job_preemptable and task_preemption_points defines a valid preemption model with bounded non-preemptive regions.
  Corollary fixed_preemption_points_model_is_valid_model_with_bounded_nonpreemptive_regions:
    valid_model_with_bounded_nonpreemptive_segments arr_seq sched.
  Proof.
    split.
    - by apply valid_fixed_preemption_points_model_lemma; destruct H_valid_fixed_preemption_points_model.
    - by apply fixed_preemption_points_model_is_model_with_bounded_nonpreemptive_regions.
  Qed.

End LimitedPreemptionsModel.

We add the above lemma into a "Hint Database" basic_rt_facts, so Coq will be able to apply them automatically.
Global Hint Resolve
     valid_fixed_preemption_points_model_lemma
     fixed_preemption_points_model_is_model_with_bounded_nonpreemptive_regions
     fixed_preemption_points_model_is_valid_model_with_bounded_nonpreemptive_regions : basic_rt_facts.