# Library prosa.analysis.abstract.restricted_supply.search_space.elf

Require Export prosa.analysis.facts.model.rbf.
Require Export prosa.analysis.abstract.search_space.
Require Export prosa.analysis.definitions.blocking_bound.elf.
Require Export prosa.analysis.facts.workload.elf_athep_bound.

# Abstract Search Space is a Subset of Restricted Supply ELF Search Space

Section SearchSpaceSubset.
Consider any type of tasks with relative priority points.
Context {Task : TaskType}.
Context `{TaskCost Task}.
Context `{TaskDeadline Task}.
Context `{TaskMaxNonpreemptiveSegment Task}.
Context `{PriorityPoint Task}.
Consider an arbitrary task set ts.
Variable ts : seq Task.
Let max_arrivals be a family of valid arrival curves.
Context `{MaxArrivals Task}.
Hypothesis H_valid_arrival_curve :
valid_taskset_arrival_curve ts max_arrivals.
Consider any FP policy.
Context {FP : FP_policy Task}.
Let tsk be any task in ts that is to be analyzed.
Variable tsk : Task.
Hypothesis H_tsk_in_ts : tsk \in ts.
Let L be an arbitrary positive constant. Normally, L denotes an upper bound on the length of a busy interval of a job of tsk. In this file, however, L can be any positive constant.
Variable L : duration.
Hypothesis H_L_positive : 0 < L.
We introduce task_rbf as an abbreviation of the task request bound function.
Let task_rbf := task_request_bound_function tsk.
To reduce the time complexity of the analysis, we introduce the notion of a search space for ELF. Intuitively, this corresponds to all "interesting" arrival offsets that the job under analysis might have with regard to the beginning of its busy window.
In the case of the search space for ELF, we consider three conditions.
First, we ask whether rbf A ≠ rbf (A + ε).
Let task_rbf_changes_at (A : duration) :=
task_rbf A != task_rbf (A + ε).
Second, we limit our search space to those arrival offsets where the bound on higher-or-equal priority workload changes in value.
Since the bound on workload from higher priority task does not depend on the arrival offset A, we are only concerned about the workload from equal priority tasks. For this, we ask whether there exists a task tsko ≠ tsk in task set ts such that ep_task_interfering_interval_length tsk tsko (A - ε) != ep_task_interfering_interval_length tsk tsko A.
Let bound_on_ep_task_workload_changes_at (A : duration) :=
let new_hep_job_released_by tsko :=
(ep_task tsk tsko) && (tsko != tsk)
&& (ep_task_interfering_interval_length tsk tsko (A - ε) != ep_task_interfering_interval_length tsk tsko A)
in has new_hep_job_released_by ts.
Third, we ask whether blocking_bound (A - ε) ≠ blocking_bound A.
Let blocking_bound_changes_at (A : duration) :=
blocking_bound ts tsk (A - ε) != blocking_bound ts tsk A.
The final search space for ELF is the set of offsets less than L and where task_rbf, blocking_bound or bound_on_ep_task_workload changes in value.
Definition is_in_search_space (A : duration) :=
(A < L) && (blocking_bound_changes_at A
|| task_rbf_changes_at A
|| bound_on_ep_task_workload_changes_at A).
To rule out pathological cases with the search space, we assume that the task cost is positive and the arrival curve is non-pathological.
Hypothesis H_task_cost_pos : 0 < task_cost tsk.
Hypothesis H_arrival_curve_pos : 0 < max_arrivals tsk ε.
For brevity, let us introduce a shorthand for an intra-IBF. The abstract search space is derived via intra-IBF.
Let intra_IBF (A F : duration) :=
task_rbf (A + ε) - task_cost tsk
+ (blocking_bound ts tsk A + bound_on_athep_workload ts tsk A F).
Then, abstract RTA's standard search space is a subset of the computation-oriented version defined above.
Lemma search_space_sub :
∀ A,
abstract.search_space.is_in_search_space L intra_IBF A →
is_in_search_space A.
Proof.
move ⇒ A [-> | [/andP [POSA LTL] [x [LTx INSP2]]]]; apply/andP; split ⇒ //.
{ apply/orP; left; apply/orP; right.
rewrite /task_rbf_changes_at /task_rbf task_rbf_0_zero //=.
{ rewrite eq_sym -lt0n add0n.
by apply task_rbf_epsilon_gt_0 ⇒ //. } }
{ apply contraT; rewrite !negb_or ⇒ /andP [/andP [/negPn/eqP PI /negPn/eqP RBF] WL].
exfalso; apply INSP2.
rewrite /intra_IBF subnK // RBF.
apply /eqP; rewrite eqn_add2l PI eqn_add2l.
rewrite /bound_on_athep_workload /bound_on_ep_task_workload /bound_on_hp_task_workload /ep_task_interfering_interval_length.
rewrite subnK //.
rewrite eqn_add2l.
apply /eqP; rewrite big_seq_cond [RHS]big_seq_cond.
apply eq_big ⇒ // tsk_i /andP [TS OTHER].
move: WL.
rewrite /bound_on_ep_task_workload_changes_at /ep_task_interfering_interval_length ⇒ /hasPn WL.
move: {WL} (WL tsk_i TS) ⇒ /nandP [/negbTE EQ|/negPn/eqP WL].
{ by move: OTHER; rewrite EQ. }
have [leq_x|gtn_x] := leqP `|Num.max 0%R (ep_task_interfering_interval_length tsk tsk_i A)| x.
{ move: WL.
rewrite subnK // /task_rbf ⇒ WL.
by rewrite WL (minn_idPl leq_x). }
move: WL.
rewrite subnK // /task_rbf ⇒ WL.
by rewrite WL (minn_idPr (ltnW gtn_x)). }
Qed.
End SearchSpaceSubset.