Library prosa.analysis.facts.model.ideal.service_of_jobs

Require Export prosa.model.schedule.scheduled.
Require Export prosa.model.aggregate.workload.
Require Export prosa.model.aggregate.service_of_jobs.
Require Export prosa.analysis.facts.model.service_of_jobs.
Require Export prosa.analysis.facts.behavior.completion.
Require Export prosa.analysis.facts.model.scheduled.

Service Received by Sets of Jobs in Uniprocessor Ideal-Progress Schedules

In this file, we establish a fact about the service received by sets of jobs in the presence of idle times on a uniprocessor under the ideal-progress assumption (i.e., that a scheduled job necessarily receives nonzero service).

Section IdealModelLemmas.

Consider any type of tasks ...

Context {Task : TaskType}.

... and any type of jobs associated with these tasks.

  Context {Job : JobType}.
  Context `{JobTask Job Task}.
  Context `{JobArrival Job}.
  Context `{JobCost Job}.

Consider any arrival sequence with consistent arrivals.

Variable arr_seq : arrival_sequence Job.
Hypothesis H_valid_arrival_sequence : valid_arrival_sequence arr_seq.

Allow for any uniprocessor model that ensures ideal progress.

  Context {PState : ProcessorState Job}.
  Hypothesis H_ideal_progress_proc_model : ideal_progress_proc_model PState.
  Hypothesis H_uniproc : uniprocessor_model PState.

Next, consider any ideal uni-processor schedule of this arrival sequence ...

  Variable sched : schedule PState.
  Hypothesis H_jobs_come_from_arrival_sequence:
    jobs_come_from_arrival_sequence sched arr_seq.

... 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.

Let P be any predicate over jobs.

Variable P : pred Job.

We prove that if the total service within some time interval [t1,t2) is smaller than t2 - t1, then there is an idle time instant t ∈ [t1,t2)].

  Lemma low_service_implies_existence_of_idle_time :
    ∀ t1 t2,
      service_of_jobs sched predT (arrivals_between arr_seq 0 t2) t1 t2 < t2 - t1 →
      ∃ t , t1 ≤ t < t2 ∧ is_idle arr_seq sched t.
  Proof.
    move⇒ t1 t2 SERV.
    destruct (t1 ≤ t2) eqn:LE; last first.
    { move: LE ⇒ /negP/negP; rewrite -ltnNge.
      move ⇒ LT; apply ltnW in LT; rewrite -subn_eq0 in LT.
      by move: LT ⇒ /eqP → in SERV; rewrite ltn0 in SERV.
    }
    have EX: ∃ δ , t2 = t1 + δ.
    { by ∃ (t2 - t1); rewrite subnKC // ltnW. }
    move: EX ⇒ [δ EQ]; subst t2; clear LE.
    rewrite {3}[t1 + δ]addnC -addnBA // subnn addn0 in SERV.
    rewrite /service_of_jobs exchange_big //= in SERV.
    apply sum_le_summation_range in SERV.
    move: SERV ⇒ [x [/andP [GEx LEx] L]].
    ∃ x; split; first by apply/andP; split.
    apply/negPn/negP; rewrite is_nonidle_iff //= ⇒ [[j SCHED]].
    move: L ⇒ /eqP; rewrite sum_nat_eq0_nat filter_predT ⇒ /allP L.
    have /eqP: service_at sched j x == 0.
    { apply/L/arrived_between_implies_in_arrivals ⇒ //.
      rewrite /arrived_between; apply/andP; split ⇒ //.
      have: job_arrival j ≤ x by apply: H_jobs_must_arrive_to_execute.
      lia. }
    by rewrite -no_service_not_scheduled // ⇒ /negP.
  Qed.

End IdealModelLemmas.