# Library prosa.analysis.definitions.priority_inversion

Require Export prosa.analysis.definitions.busy_interval.classical.

Require Export prosa.analysis.facts.model.scheduled.

Require Export prosa.analysis.facts.model.scheduled.

# Priority Inversion

In this section, we define the notion of priority inversion for arbitrary processors.
Consider any type of tasks ...

... and any type of jobs associated with these tasks.

Context {Job : JobType}.

Context `{JobTask Job Task}.

Context `{JobArrival Job}.

Context `{JobCost Job}.

Context `{JobTask Job Task}.

Context `{JobArrival Job}.

Context `{JobCost Job}.

Next, consider

*any*kind of processor state model, ...
... any arrival sequence, ...

... and any schedule.

Assume a given JLFP policy.

Consider an arbitrary job.

We say that the job incurs priority inversion if it has higher
priority than the scheduled job. Note that this definition is
oblivious to whether job j is ready. Therefore, it may not
apply as intuitively expected in models with jitter or
self-suspensions. Further generalization of the concept is
likely necessary to efficiently analyze models in which jobs may
be pending without being ready.

Definition priority_inversion (t : instant) :=

(j \notin scheduled_jobs_at arr_seq sched t)

&& has (fun jlp ⇒ ~~ hep_job jlp j) (scheduled_jobs_at arr_seq sched t).

(j \notin scheduled_jobs_at arr_seq sched t)

&& has (fun jlp ⇒ ~~ hep_job jlp j) (scheduled_jobs_at arr_seq sched t).

Similarly we define priority inversion occurring only due to jobs
satisfying the predicate P. In other words, the lower-priority job
scheduled instead of j satisfies the predicate P.

Definition priority_inversion_cond (P : pred Job) (t : instant) :=

(j \notin scheduled_jobs_at arr_seq sched t)

&& has (fun jlp ⇒ ~~ hep_job jlp j && P jlp) (scheduled_jobs_at arr_seq sched t).

(j \notin scheduled_jobs_at arr_seq sched t)

&& has (fun jlp ⇒ ~~ hep_job jlp j && P jlp) (scheduled_jobs_at arr_seq sched t).

Cumulative priority inversion incurred by a job within some time
interval

`[t1, t2)`

is the total number of time instances
within `[t1,t2)`

at which job j incurred priority
inversion.
Definition cumulative_priority_inversion (t1 t2 : instant) :=

\sum_(t1 ≤ t < t2) priority_inversion t.

\sum_(t1 ≤ t < t2) priority_inversion t.

Cumulative priority inversion incurred by a job from jobs satisfying
a predefined condition P within some time interval

`[t1, t2)`

is the total number of time instances within `[t1, t2)`

at which job j incurred priority inversion due to jobs satisfying P.
Definition cumulative_priority_inversion_cond (P : pred Job) (t1 t2 : instant) :=

\sum_(t1 ≤ t < t2) priority_inversion_cond P t.

\sum_(t1 ≤ t < t2) priority_inversion_cond P t.

Suppose the priority inversion experienced by job j depends on
its relative arrival time w.r.t. the beginning of its busy
interval at a time t1. We say that the priority inversion of
job j is bounded by a function B : duration → duration if
the cumulative priority inversion within any busy interval
prefix is bounded by B (job_arrival j - t1).

Definition priority_inversion_of_job_is_bounded_by (B : duration → duration) :=

∀ (t1 t2 : instant),

busy_interval_prefix arr_seq sched j t1 t2 →

cumulative_priority_inversion t1 t2 ≤ B (job_arrival j - t1).

∀ (t1 t2 : instant),

busy_interval_prefix arr_seq sched j t1 t2 →

cumulative_priority_inversion t1 t2 ≤ B (job_arrival j - t1).

We define a similar notion as defined above for the priority
inversion that is experienced by a job due to jobs satisfying
the predicate P.

Definition priority_inversion_of_job_cond_is_bounded_by (P : pred Job) (B : duration → duration) :=

∀ (t1 t2 : instant),

busy_interval_prefix arr_seq sched j t1 t2 →

cumulative_priority_inversion_cond P t1 t2 ≤ B (job_arrival j - t1).

End PriorityInversion.

∀ (t1 t2 : instant),

busy_interval_prefix arr_seq sched j t1 t2 →

cumulative_priority_inversion_cond P t1 t2 ≤ B (job_arrival j - t1).

End PriorityInversion.

In this section, we define a notion of the bounded priority inversion for tasks.

Consider any type of tasks ...

... and any type of jobs associated with these tasks.

Context {Job : JobType}.

Context `{JobTask Job Task}.

Context `{JobArrival Job}.

Context `{JobCost Job}.

Context `{JobTask Job Task}.

Context `{JobArrival Job}.

Context `{JobCost Job}.

Next, consider

*any*kind of processor state model, ...
... any arrival sequence, ...

... and any schedule.

Assume a given JLFP policy.

Consider an arbitrary task tsk.

We say that task tsk has bounded priority inversion if all its
jobs have bounded cumulative priority inversion that depends on
its relative arrival time w.r.t. the beginning of the busy
interval.

Definition priority_inversion_is_bounded_by (B : duration → duration) :=

∀ (j : Job),

arrives_in arr_seq j →

job_of_task tsk j →

job_cost j > 0 →

priority_inversion_of_job_is_bounded_by arr_seq sched j B.

∀ (j : Job),

arrives_in arr_seq j →

job_of_task tsk j →

job_cost j > 0 →

priority_inversion_of_job_is_bounded_by arr_seq sched j B.