# Library prosa.analysis.facts.model.arrival_curves

Require Export prosa.util.epsilon.
Require Export prosa.model.priority.classes.
Require Export prosa.model.task.arrival.curves.
Require Export prosa.analysis.facts.model.task_arrivals.

# Facts About Arrival Curves

We observe that tasks that exhibit job arrivals must have non-pathological arrival curves. This allows excluding pathological cases in higher-level proofs.
Section NonPathologicalCurve.
Consider any kind of tasks characterized by an upper-bounding arrival curve...
Context {Task : TaskType} `{MaxArrivals Task}.
... and the corresponding type of jobs.
Context {Job : JobType} `{JobTask Job Task}.
Consider an arbitrary task ...
Variable tsk : Task.
... and an arrival sequence ...
Variable arr_seq : arrival_sequence Job.
... that is compliant with the upper-bounding arrival curve.
Hypothesis H_curve_is_valid : respects_max_arrivals arr_seq tsk (max_arrivals tsk).
If we have evidence that a job of the task tsk ...
Variable j : Job.
Hypothesis H_job_of_tsk : job_of_task tsk j.
... arrives at any point in time, ...
Hypothesis H_arrives : arrives_in arr_seq j.
... then the maximum number of job arrivals in a non-empty interval cannot be zero.
Lemma non_pathological_max_arrivals :
max_arrivals tsk ε > 0.
Proof.
move: (H_arrives) ⇒ [t ARR].
move: (H_curve_is_valid t t.+1 ltac:(by done)).
rewrite -addn1 -addnBAC // addnBl_leq // ⇒ VALID.
apply: (leq_trans _ VALID).
rewrite /number_of_task_arrivals size_of_task_arrivals_between.
rewrite big_ltn addn1 // big_geq // addn0.
rewrite /task_arrivals_at size_filter //= -has_count.
by apply /hasP; ∃ j.
Qed.
End NonPathologicalCurve.
We add the above lemma to the global hints database.
Global Hint Resolve non_pathological_max_arrivals : basic_rt_facts.
In the following section, we prove a bound on the number of arrivals within a given interval under an arbitrary JLFP policy.
Section JLFPArrivalBounds.
Consider any type of tasks ...
Context {Task : TaskType}.
Context `{MaxArrivals Task}.
... and the corresponding type of jobs.
Context {Job : JobType}.
Context `{JobTask Job Task}.
Context `{JobArrival Job}.
Context `{JLFP_policy Job}.
Consider any kind of processor state model...
Context {PState : ProcessorState Job}.
... and arrival sequence.
Variable arr_seq : arrival_sequence Job.
We consider an arbitrary task set ts ...
Variable ts : seq Task.
... and assume that all jobs stem from tasks in this task set.
Hypothesis H_all_jobs_from_taskset : all_jobs_from_taskset arr_seq ts.
We assume that max_arrivals is a family of valid arrival curves that constrains the arrival sequence arr_seq, i.e., for any task tsk in ts, max_arrival tsk is an arrival bound of tsk.
Hypothesis H_is_arrival_curve : taskset_respects_max_arrivals arr_seq ts.
We prove that the number of jobs that arrive in the interval `[t1, t1 + Δ)` and have higher-or-equal priority than a given job j is bounded by the sum of arrival curves for all tasks in ts.
Lemma jlfp_hep_arrivals_bounded_by_sum_max_arrivals :
∀ (j : Job) (t1 : instant) (Δ : duration),
size [seq jhp <- arrivals_between arr_seq t1 (t1 + Δ) | hep_job jhp j]
≤ \sum_(tsk <- ts) max_arrivals tsk Δ.
Proof.
move⇒ j t1 Δ; rewrite -sum1_size big_filter.
apply leq_trans with (\sum_(i <- arrivals_between arr_seq t1 (t1 + Δ)) 1).
{ by rewrite big_mkcond //=; apply leq_sum ⇒ i _ ; destruct hep_job. }
apply: leq_trans.
{ apply sum_over_partitions_le with (x_to_y := job_task) (ys := ts) ⇒ s IN HEP.
by eapply H_all_jobs_from_taskset, in_arrivals_implies_arrived ⇒ //. }
{ rewrite big_seq_cond [leqRHS]big_seq_cond; apply leq_sum ⇒ tsk /andP [IN _].
rewrite -big_filter sum1_size -{2}[Δ](addKn t1).
apply:leq_trans; last by apply H_is_arrival_curve ⇒ //; lia.
by rewrite /number_of_task_arrivals /task_arrivals_between -sum1_size big_filter. }
Qed.
End JLFPArrivalBounds.
In this section, we prove a bound on the number of arrivals within a given interval under an FP policy.
Section FPArrivalBounds.
Consider any type of tasks ...
Context {Task : TaskType}.
Context `{MaxArrivals Task}.
... and their associated jobs.
Context {Job : JobType}.
Context `{JobTask Job Task}.
Context `{JobArrival Job}.
Allow for any fixed-priority policy.
Context `{FP_policy Task}.
Consider any kind of processor state model...
Context {PState : ProcessorState Job}.
... and arrival sequence.
Variable arr_seq : arrival_sequence Job.
We consider an arbitrary task set ts ...
Variable ts : seq Task.
... and assume that all jobs stem from tasks in this task set.
Hypothesis H_all_jobs_from_taskset : all_jobs_from_taskset arr_seq ts.
We assume that max_arrivals is a family of valid arrival curves that constrains the arrival sequence arr_seq, i.e., for any task tsk in ts, max_arrival tsk is an arrival bound of tsk.
Hypothesis H_is_arrival_curve : taskset_respects_max_arrivals arr_seq ts.
We prove that the number of jobs that arrive in the interval `[t1, t1 + Δ)` and have higher-or-equal priority than a given job j is bounded by the sum of arrival curves of all tasks in ts whose priority is higher than or equal to that of j’s task.
Lemma fp_hep_arrivals_bounded_by_sum_max_arrivals :
∀ (j : Job) (t1 : instant) (Δ : duration),
size [seq jhp <- arrivals_between arr_seq t1 (t1 + Δ) | hep_job jhp j]
≤ \sum_(tsk <- ts | hep_task tsk (job_task j)) max_arrivals tsk Δ.
Proof.
move⇒ j t1 Δ; rewrite -sum1_size big_filter.
apply leq_trans with (
\sum_(i <- arrivals_between arr_seq t1 (t1 + Δ) | hep_task (job_task i) (job_task j)) 1
).
{ by rewrite big_mkcond //=; apply leq_sum ⇒ i _ ; destruct hep_job. }
apply: leq_trans.
{ apply sum_over_partitions_le with (x_to_y := job_task) (ys := ts) ⇒ s IN HEP.
by eapply H_all_jobs_from_taskset, in_arrivals_implies_arrived ⇒ //. }
{ rewrite big_seq_cond [leqRHS]big_seq_cond.
rewrite big_mkcond [leqRHS]big_mkcond //=; apply leq_sum ⇒ tsk _.
destruct (tsk \in ts) eqn:IN; last by done.
rewrite //=; destruct (hep_task tsk (job_task j)) eqn:HEP.
{ rewrite -big_filter sum1_size -{2}[Δ](addKn t1).
apply: leq_trans; last eapply H_is_arrival_curve.
{ rewrite /number_of_task_arrivals /task_arrivals_between -!sum1_size !big_filter.
rewrite big_seq_cond [leqRHS]big_seq_cond.
rewrite big_mkcond [leqRHS]big_mkcond //=.
apply leq_sum ⇒ s _; rewrite /job_of_task.
by destruct (_ == _), (s \in _ ), (hep_task _ _), (hep_task _ _) ⇒ //.
}
{ by done. }
{ by lia. }
}
{ rewrite big_seq_cond leqn0; apply/eqP; apply big1 ⇒ s /andP [INs /andP [HEPs /eqP EQs]].
by subst tsk; rewrite HEP in HEPs.
}
}
Qed.
End FPArrivalBounds.