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Commit 1467b2e6 authored by Felipe Cerqueira's avatar Felipe Cerqueira
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Prove admit in FP computation

parent 78938289
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bertogna_fp_comp.v
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......@@ -53,9 +53,9 @@ Module ResponseTimeIterationFP.
(task_cost tsk).
(* To ensure that the iteration converges, we will apply per_task_rta
a "sufficient" number of times: task_deadline tsk - task_cost tsk.
a "sufficient" number of times: task_deadline tsk - task_cost tsk + 1.
This corresponds to the time complexity of the iteration. *)
Definition max_steps (tsk: sporadic_task) := task_deadline tsk - task_cost tsk.
Definition max_steps (tsk: sporadic_task) := task_deadline tsk - task_cost tsk + 1.
(* Next we compute the response-time bounds for the entire task set.
Since high-priority tasks may not be schedulable, we allow the
......@@ -125,7 +125,7 @@ Module ResponseTimeIterationFP.
rewrite eqseq_rcons in EQ.
move: EQ => /andP [_ /eqP EQ].
by inversion EQ.
Qed.
Qed.
(* The response-time bounds computed using R_list are based on the per-task
fixed-point iteration. *)
......@@ -409,18 +409,20 @@ Module ResponseTimeIterationFP.
(* In this section, we show that the fixed-point iteration converges. *)
Section Convergence.
(* Consider any valid set of higher-priority tasks. *)
(* Consider any set of higher-priority tasks. *)
Variable ts_hp: taskset_of sporadic_task.
Hypothesis valid_task_parameters:
valid_sporadic_taskset task_cost task_period task_deadline ts_hp.
(* Assume that the response-time analysis succeeds. *)
(* Assume that the response-time analysis succeeds for the higher-priority tasks. *)
Variable rt_bounds: seq task_with_response_time.
Hypothesis H_test_succeeds: R_list ts_hp = Some rt_bounds.
(* Consider any task tsk to be analyzed. *)
(* Consider any task tsk to be analyzed, ... *)
Variable tsk: sporadic_task.
(* ... and assume all tasks have valid parameters. *)
Hypothesis H_valid_task_parameters:
valid_sporadic_taskset task_cost task_period task_deadline (rcons ts_hp tsk).
(* To simplify, let f denote the fixed-point iteration. *)
Let f := per_task_rta tsk rt_bounds.
......@@ -433,7 +435,7 @@ Module ResponseTimeIterationFP.
Proof.
unfold valid_sporadic_taskset, is_valid_sporadic_task in *.
rename H_test_succeeds into SOME,
valid_task_parameters into VALID.
H_valid_task_parameters into VALID.
intros x1 x2 LEx; unfold f, per_task_rta.
apply fun_mon_iter_mon; [by ins | by ins; apply leq_addr |].
clear LEx x1 x2; intros x1 x2 LEx.
......@@ -451,7 +453,7 @@ Module ResponseTimeIterationFP.
rewrite leq_min; apply/andP; split.
{
apply leq_trans with (n := W task_cost task_period i R x1); first by apply geq_minl.
specialize (VALID i IN); des.
exploit (VALID i); [by rewrite mem_rcons in_cons IN orbT | ins; des].
by apply W_monotonic; try (by ins);
[by apply GE_COST | by apply leqnn].
}
......@@ -463,10 +465,10 @@ Module ResponseTimeIterationFP.
(* If the iteration converged at an earlier step, then it remains stable. *)
Lemma bertogna_fp_comp_f_converges_early :
(exists k, k < max_steps tsk /\ f k = f k.+1) ->
(exists k, k <= max_steps tsk /\ f k = f k.+1) ->
f (max_steps tsk) = f (max_steps tsk).+1.
Proof.
by intros EX; des; apply iter_fix with (k := k); [by done | by apply ltnW].
by intros EX; des; apply iter_fix with (k := k).
Qed.
(* Else, we derive a contradiction. *)
......@@ -475,12 +477,12 @@ Module ResponseTimeIterationFP.
(* Assume instead that the iteration continued to diverge. *)
Hypothesis H_keeps_diverging:
forall k,
k < max_steps tsk -> f k != f k.+1.
k <= max_steps tsk -> f k != f k.+1.
(* By monotonicity, it follows that the value always increases. *)
Lemma bertogna_fp_comp_f_increases :
forall k,
k < max_steps tsk ->
k <= max_steps tsk ->
f k < f k.+1.
Proof.
intros k LT.
......@@ -490,16 +492,35 @@ Module ResponseTimeIterationFP.
Qed.
(* In the end, the response-time bound must exceed the deadline. Contradiction! *)
Lemma bertogna_fp_comp_rt_exceeds_deadline :
f (max_steps tsk) > task_deadline tsk.
Lemma bertogna_fp_comp_rt_grows_too_much :
forall k,
k <= max_steps tsk ->
f k > k + task_cost tsk - 1.
Proof.
unfold max_steps.
induction (task_deadline tsk).
rename H_valid_task_parameters into TASK_PARAMS.
unfold valid_sporadic_taskset, is_valid_sporadic_task in *; des.
exploit (TASK_PARAMS tsk);
[by rewrite mem_rcons in_cons eq_refl orTb | intro PARAMS; des].
induction k.
{
simpl.
admit.
intros _; rewrite add0n -addn1 subh1;
first by rewrite -addnBA // subnn addn0 /= leqnn.
by apply PARAMS.
}
admit.
{
intros LT.
specialize (IHk (ltnW LT)).
apply leq_ltn_trans with (n := f k);
last by apply bertogna_fp_comp_f_increases, ltnW.
rewrite -addn1 -addnA [1 + _]addnC addnA -addnBA // subnn addn0.
rewrite -(ltn_add2r 1) in IHk.
rewrite subh1 in IHk; last first.
{
apply leq_trans with (n := task_cost tsk); last by apply leq_addl.
by apply PARAMS.
}
by rewrite -addnBA // subnn addn0 addn1 ltnS in IHk.
}
Qed.
End DerivingContradiction.
......@@ -508,15 +529,16 @@ Module ResponseTimeIterationFP.
Lemma per_task_rta_converges:
f (max_steps tsk) = f (max_steps tsk).+1.
Proof.
unfold valid_sporadic_taskset, is_valid_sporadic_task in *.
rename H_no_larger_than_deadline into LE.
rename H_no_larger_than_deadline into LE,
H_valid_task_parameters into TASK_PARAMS.
unfold valid_sporadic_taskset, is_valid_sporadic_task in *; des.
(* Either f converges by the deadline or not. *)
destruct ([exists k in 'I_(max_steps tsk), f k == f k.+1]) eqn:EX.
destruct ([exists k in 'I_(max_steps tsk).+1, f k == f k.+1]) eqn:EX.
{
move: EX => /exists_inP EX; destruct EX as [k _ ITERk].
apply bertogna_fp_comp_f_converges_early.
by exists k; split; [by apply ltn_ord | by apply/eqP].
by exists k; split; [by rewrite -ltnS; apply ltn_ord | by apply/eqP].
}
(* If not, then we reach a contradiction *)
......@@ -524,7 +546,18 @@ Module ResponseTimeIterationFP.
move: EX => /forall_inP EX.
rewrite leqNgt in LE; move: LE => /negP LE.
exfalso; apply LE.
by apply bertogna_fp_comp_rt_exceeds_deadline.
have TOOMUCH := bertogna_fp_comp_rt_grows_too_much _ (max_steps tsk).
exploit TOOMUCH; [| by apply leqnn |].
{
intros k LEk; rewrite -ltnS in LEk.
by exploit (EX (Ordinal LEk)); [by done | intro DIFF].
}
unfold max_steps at 1.
exploit (TASK_PARAMS tsk);
[by rewrite mem_rcons in_cons eq_refl orTb | intro PARAMS; des].
rewrite -addnA [1 + _]addnC addnA -addnBA // subnn addn0.
rewrite subh1; last by apply PARAMS2.
by rewrite -addnBA // subnn addn0.
Qed.
End Convergence.
......@@ -704,7 +737,8 @@ Module ResponseTimeIterationFP.
by ins; apply R_list_le_deadline with (ts' := ts') (rt_bounds := hp_bounds).
{
rewrite [R_lst](R_list_rcons_response_time ts' hp_bounds tsk_lst); last by ins.
rewrite per_task_rta_fold; apply per_task_rta_converges.
rewrite per_task_rta_fold.
apply per_task_rta_converges with (ts_hp := ts'); try (by done).
apply R_list_le_deadline with (ts' := rcons ts' tsk_lst)
(rt_bounds := rcons hp_bounds (tsk_lst, R_lst));
first by apply SOME'.
......
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