Library prosa.analysis.facts.busy_interval.priority_inversion

Lemma about Priority Inversion for arbitrary processors

In this section, we prove a lemma about the notion of priority inversion for arbitrary processors.
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}.

Next, consider any kind of processor state model, ...
  Context {PState : ProcessorState Job}.

... any arrival sequence, ...
  Variable arr_seq : arrival_sequence Job.

... and any schedule.
  Variable sched : schedule PState.

Assume a given JLFP policy.
  Context `{JLFP_policy Job}.

Consider an arbitrary job.
  Variable j : Job.

Then we prove that cumulative priority inversion (CPI) that job j incurs in an interval [t1, t2) is equal to the sum of CPI in an interval [t1, t_mid) and CPI in an interval [t_mid, t2).
  Lemma cumulative_priority_inversion_cat:
     (t_mid t1 t2 : instant),
      t1 t_mid
      t_mid t2
      cumulative_priority_inversion arr_seq sched j t1 t2 =
        cumulative_priority_inversion arr_seq sched j t1 t_mid
        + cumulative_priority_inversion arr_seq sched j t_mid t2.
    intros × LE1 LE2.
    rewrite /cumulative_priority_inversion -big_cat //=.
    replace (index_iota t1 t_mid ++ index_iota t_mid t2) with (index_iota t1 t2); first by reflexivity.
    interval_to_duration t1 t_mid δ1.
    interval_to_duration (t1 + δ1) t2 δ2.
    rewrite -!addnA /index_iota.
    erewrite iotaD_impl with (n_le := δ1); last by lia.
    by rewrite !addKn addnA addKn.

Assume that j is scheduled at time t, then there is no priority inversion at time t.
  Lemma sched_itself_implies_no_priority_inversion :
      scheduled_at sched j t
      priority_inversion_dec arr_seq sched j t = false.
  Proof. by movet SCHED; rewrite /priority_inversion_dec SCHED. Qed.

End PIGenericProcessorModelLemma.