Library rt.model.schedule.apa.interference

Require Import rt.util.all.
Require Import rt.model.arrival.basic.job rt.model.arrival.basic.task rt.model.priority.
Require Import
Require Import
Require Import rt.model.schedule.apa.affinity.
From mathcomp Require Import ssreflect ssrbool eqtype ssrnat seq fintype bigop.

Module Interference.

  Import Schedule ScheduleOfSporadicTask Priority Workload Affinity.

  (* In this section, we define the notion of a possible interfering task. *)
  Section PossibleInterferingTasks.

    Context {sporadic_task: eqType}.
    Variable task_cost: sporadic_task time.
    Variable task_period: sporadic_task time.
    Variable task_deadline: sporadic_task time.

    (* Consider an APA platform with affinity alpha. *)
    Context {num_cpus: nat}.
    Variable alpha: task_affinity sporadic_task num_cpus.

    Section FP.

      (* Assume an FP policy. *)
      Variable higher_eq_priority: FP_policy sporadic_task.

      (* Let tsk be the task to be analyzed ... *)
      Variable tsk: sporadic_task.

      (* ...assuming a subaffinity alpha'. *)
      Variable alpha': affinity num_cpus.

      (* Let tsk_other be another task. *)
      Variable tsk_other: sporadic_task.

      (* Under FP scheduling with constrained deadlines, tsk_other can only interfere
         with tsk if it is a different task with higher or equal priority and
         intersecting affinity. *)

      Definition higher_priority_task_in :=
        higher_eq_priority tsk_other tsk &&
        (tsk_other != tsk) &&
        affinity_intersects alpha' (alpha tsk_other).

    End FP.

    Section JLFP.

      (* Let tsk be the task to be analyzed ... *)
      Variable tsk: sporadic_task.

      (* ...assuming a subaffinity alpha'. *)
      Variable alpha': affinity num_cpus.

      (* Let tsk_other be another task. *)
      Variable tsk_other: sporadic_task.

      (* Under JLFP/JLDP scheduling with constrained deadlines, tsk_other can only interfere
         with tsk if it is a different task with intersecting affinity. *)

      Definition different_task_in :=
        (tsk_other != tsk) &&
        affinity_intersects alpha' (alpha tsk_other).

    End JLFP.

  End PossibleInterferingTasks.

  Section InterferenceDefs.

    Context {sporadic_task: eqType}.
    Context {Job: eqType}.
    Variable job_arrival: Job time.
    Variable job_cost: Job time.
    Variable job_task: Job sporadic_task.

    (* Assume any job arrival sequence...*)
    Context {arr_seq: arrival_sequence Job}.

    (* ... and any schedule. *)
    Context {num_cpus: nat}.
    Variable sched: schedule Job num_cpus.

    (* Assume that every job at any time has a processor affinity alpha. *)
    Variable alpha: task_affinity sporadic_task num_cpus.

    (* Consider any job j that incurs interference. *)
    Variable j: Job.

    (* Recall the definition of backlogged (pending and not scheduled). *)
    Let job_is_backlogged (t: time) := backlogged job_arrival job_cost sched j t.

    (* First, we define total interference. *)
    Section TotalInterference.

      (* The total interference incurred by job j during [t1, t2) is the
         cumulative time in which j is backlogged in this interval. *)

      Definition total_interference (t1 t2: time) :=
        \sum_(t1 t < t2) job_is_backlogged t.

    End TotalInterference.

    (* Next, we define job interference. *)
    Section JobInterference.

      (* Let job_other be a job that interferes with j. *)
      Variable job_other: Job.

      (* The interference caused by job_other during [t1, t2) is the cumulative
         time in which j is backlogged while job_other is scheduled. *)

      Definition job_interference (t1 t2: time) :=
        \sum_(t1 t < t2)
          \sum_(cpu < num_cpus)
            (job_is_backlogged t &&
            can_execute_on alpha (job_task j) cpu &&
            scheduled_on sched job_other cpu t).

    End JobInterference.

    (* Next, we define task interference. *)
    Section TaskInterference.

      (* Consider any interfering task tsk_other. *)
      Variable tsk_other: sporadic_task.

      (* The interference caused by tsk during [t1, t2) is the cumulative time
         in which j is backlogged while tsk is scheduled. *)

      Definition task_interference (t1 t2: time) :=
        \sum_(t1 t < t2)
          \sum_(cpu < num_cpus)
            (job_is_backlogged t &&
            can_execute_on alpha (job_task j) cpu &&
            task_scheduled_on job_task sched tsk_other cpu t).

    End TaskInterference.

    (* Next, we define an approximation of the total interference based on
       each per-task interference. *)

    Section TaskInterferenceJobList.

      Variable tsk_other: sporadic_task.

      Definition task_interference_joblist (t1 t2: time) :=
        \sum_(j <- jobs_scheduled_between sched t1 t2 | job_task j == tsk_other)
         job_interference j t1 t2.

    End TaskInterferenceJobList.

    (* Now we prove some basic lemmas about interference. *)
    Section BasicLemmas.

      (* Total interference cannot be larger than the considered time window. *)
      Lemma total_interference_le_delta :
         t1 t2,
          total_interference t1 t2 t2 - t1.
        unfold total_interference; intros t1 t2.
        apply leq_trans with (n := \sum_(t1 t < t2) 1);
          first by apply leq_sum; ins; apply leq_b1.
        by rewrite big_const_nat iter_addn mul1n addn0 leqnn.

      (* Job interference is bounded by the service of the interfering job. *)
      Lemma job_interference_le_service :
         j_other t1 t2,
          job_interference j_other t1 t2 service_during sched j_other t1 t2.
        intros j_other t1 t2; unfold job_interference, service_during.
        apply leq_sum; intros t _.
        unfold service_at; rewrite [\sum_(_ < _ | scheduled_on _ _ _ _)_]big_mkcond.
        apply leq_sum; intros cpu _.
        destruct (job_is_backlogged t); [rewrite andTb | by rewrite andFb].
        destruct (can_execute_on alpha (job_task j) cpu); [rewrite andTb | by rewrite andFb].
        by destruct (scheduled_on sched j_other cpu t).

      (* Task interference is bounded by the workload of the interfering task. *)
      Lemma task_interference_le_workload :
         tsk t1 t2,
          task_interference tsk t1 t2 workload job_task sched tsk t1 t2.
        unfold task_interference, workload; intros tsk t1 t2.
        apply leq_sum; intros t _.
        apply leq_sum; intros cpu _.
        destruct (job_is_backlogged t); [rewrite andTb | by rewrite andFb].
        destruct (can_execute_on alpha (job_task j) cpu); [rewrite andTb | by rewrite andFb].
        unfold task_scheduled_on, service_of_task.
        by destruct (sched cpu t).

    End BasicLemmas.

    (* Now we prove some bounds on interference for sequential jobs. *)
    Section InterferenceNoParallelism.

      (* If jobs are sequential, ... *)
      Hypothesis H_sequential_jobs: sequential_jobs sched.

      (* ... then the interference incurred by a job in an interval
         of length delta is at most delta. *)

      Lemma job_interference_le_delta :
         j_other t1 delta,
          job_interference j_other t1 (t1 + delta) delta.
        rename H_sequential_jobs into SEQ.
        unfold job_interference, sequential_jobs in ×.
        intros j_other t1 delta.
        apply leq_trans with (n := \sum_(t1 t < t1 + delta) 1);
          last by rewrite big_const_nat iter_addn mul1n addn0 addKn leqnn.
        apply leq_sum; intros t _.
        destruct ([ cpu, scheduled_on sched j_other cpu t]) eqn:EX.
          move: EX ⇒ /existsP [cpu SCHED].
          rewrite (bigD1 cpu) // /=.
          rewrite big_mkcond (eq_bigr (fun x ⇒ 0)) /=;
            first by simpl_sum_const; rewrite leq_b1.
          intros cpu' _; des_if_goal; last by done.
          destruct (scheduled_on sched j_other cpu' t) eqn:SCHED'; last by rewrite andbF.
          move: SCHED SCHED' ⇒ /eqP SCHED /eqP SCHED'.
          by specialize (SEQ j_other t cpu cpu' SCHED SCHED'); rewrite SEQ in Heq.
          apply negbT in EX; rewrite negb_exists in EX.
          move: EX ⇒ /forallP EX.
          rewrite (eq_bigr (fun x ⇒ 0)); first by simpl_sum_const.
          by intros cpu _; specialize (EX cpu); apply negbTE in EX; rewrite EX andbF.

    End InterferenceNoParallelism.

    (* Next, we show that the cumulative per-task interference bounds the total
       interference. *)

    Section BoundUsingPerTaskInterference.

      Lemma interference_le_interference_joblist :
         tsk t1 t2,
          task_interference tsk t1 t2 task_interference_joblist tsk t1 t2.
        intros tsk t1 t2.
        unfold task_interference, task_interference_joblist, job_interference, job_is_backlogged.
        rewrite [\sum_(_ <- _ sched _ _ | _) _]exchange_big /=.
        rewrite big_nat_cond [\sum_(_ _ < _ | true) _]big_nat_cond.
        apply leq_sum; movet /andP [LEt _].
        rewrite exchange_big /=.
        apply leq_sum; intros cpu _.
        destruct (backlogged job_arrival job_cost sched j t) eqn:BACK;
          last by rewrite andFb (eq_bigr (fun x ⇒ 0));
            first by rewrite big_const_seq iter_addn mul0n addn0.
        rewrite andTb.
        destruct (task_scheduled_on job_task sched tsk cpu t) eqn:SCHED;
          [rewrite andbT | by rewrite andbF].
        unfold scheduled_on, task_scheduled_on in ×.
        destruct (sched cpu t) as [j' |] eqn:SOME; last by done.
        rewrite big_mkcond /= (bigD1_seq j') /=; last by apply undup_uniq.
          by rewrite SCHED eq_refl andbT leq_addr.
          unfold jobs_scheduled_between.
          rewrite mem_undup; apply mem_bigcat_nat with (j := t);
            first by done.
          apply mem_bigcat_ord with (j := cpu); first by apply ltn_ord.
          by unfold make_sequence; rewrite SOME mem_seq1 eq_refl.

    End BoundUsingPerTaskInterference.

  End InterferenceDefs.

End Interference.