KR101335038B1 - Periodic and aperiodic task scheduling algorithm based on topological sort and residual time - Google Patents

Abstract

Embodiments of the present invention relate to a technique for scheduling and processing tasks in a real-time system, and more particularly, to an algorithm for efficiently scheduling and processing each of tasks in consideration of characteristics of the tasks. In particular, according to the embodiment of the present invention, the surplus time remaining by the scheduling time of the scheduling and periodic tasks, which can perform periodic tasks and aperiodic real-time tasks together in one system, and satisfy the preceding relationship between the periodic tasks. Scheduling is possible to efficiently execute acyclic real-time tasks.

Description

Periodic and non-periodic real-time task scheduling algorithm based on phase alignment and surplus time {PERIODIC AND APERIODIC TASK SCHEDULING ALGORITHM BASED ON TOPOLOGICAL SORT AND RESIDUAL TIME}

The following embodiment relates to a technique for scheduling and processing tasks in a real-time system, and more particularly, to an algorithm for efficiently scheduling and processing each task in consideration of characteristics of the tasks.

A typical real time system handles tasks including aperiodic real time tasks, periodic tasks and non real time tasks. In particular, the periodic task is a task performed according to a specific period, and may be divided into generating data, receiving a task from another task, processing the task, and transmitting the data to another task, and processing only data transmitted from another task.

Since these periodic tasks have a predecessor in their operation, they need to be performed all within the period as much as possible, and also need to generate and use data in accordance with established prior constraints. Therefore, since scheduling of a real-time system related to a periodic task is known as an NP-Nard problem, techniques for obtaining a suboptimal solution rather than an optimum using a heuristic method have been studied. In addition, a scheduling technique for processing a periodic task together with an aperiodic real-time task that processes an event occurring at an unspecified time such as an alarm has also been studied.

Meanwhile, scheduling of a real-time system may be classified into on-line scheduling and off-line scheduling according to a time point at which scheduling is performed. Online scheduling is a matter of flexibility, but there may be limitations in solving problems such as precedence constraints between tasks.

In addition, the offline scheduling method may not be suitable for scheduling non-periodic real-time tasks that occur at an unspecified time since the offline scheduling method preallocates the uptime or priority of periodic tasks prior to the performance of the system.

According to an embodiment of the present invention, a periodic and aperiodic real time task scheduling algorithm based on phase alignment and surplus time that can perform a periodic task and an aperiodic real time task in one system can be provided.

In particular, according to an embodiment of the present invention, it is possible to schedule to satisfy the preceding relationship between the periodic tasks, phase alignment that can be scheduled to execute aperiodic real-time task in the surplus time remaining by the scheduling time of the periodic tasks And a periodic and aperiodic real-time task scheduling algorithm based on the surplus time.

A method of performing a scheduling algorithm according to an embodiment of the present invention, comprising: a method of performing a scheduling algorithm in a system for performing a plurality of periodic tasks and at least one aperiodic real-time task, the preceding relation of the plurality of periodic tasks In consideration of the above, performing the scheduling of each of the plurality of periodic tasks, and if the scheduling of the at least one aperiodic real-time task is requested from the system, a surplus time of the scheduling time of the plurality of periodic tasks Scheduling the at least one aperiodic real-time task for.

In this case, the scheduling of each of the plurality of periodic tasks may be performed based on a period and an execution order of each of the plurality of periodic tasks. Can be scheduled.

In addition, performing scheduling of each of the plurality of periodic tasks may include repeatedly deleting a task of a vertex having an entry order of zero on a graph structure among the plurality of periodic tasks, and periodically deleting the repeated periodic tasks. The method may include performing a phase alignment according to the deleting order, assigning priorities, and scheduling the plurality of periodic tasks in consideration of the assigned priorities.

In addition, when there are a plurality of tasks of a vertex having an entry order of 0, the step of repeatedly deleting the tasks of a vertex having an entry order of zero compares periods of a plurality of tasks of the vertices and performs a period according to the comparison result. Can delete the shorter task first.

In addition, the method of performing the scheduling algorithm may be configured to determine whether the scheduling is requested according to a residual time by a scheduling time of the plurality of periodic tasks and whether the scheduling is greater than an execution time of the requested aperiodic real-time task. The method may further include accepting execution of the periodic real-time task.

The scheduling algorithm may further include allocating a priority of the aperiodic realtime task for which the scheduling is requested to the highest level when execution of the aperiodic realtime task for which the scheduling is requested is accepted, and a threshold of the plurality of periodic tasks. The method may further include updating a time and, if there is a periodic task of a critical time at which the deadline is imminent by the updating, performing the periodic task of which the deadline is imminent before the aperiodic real-time task.

In addition, the performing of the periodic task near the end of the non-periodic real-time task is the step of setting the priority of the non-periodic real-time task to the lowest, executing the periodic task that is close to the deadline, the deadline When execution of the impending periodic task is finished, resetting the priority of the aperiodic real-time task to the highest level.

According to another aspect of the present invention, there is provided a scheduling apparatus in a system for performing a plurality of periodic tasks and at least one aperiodic real-time task, in consideration of a preceding relationship between the plurality of periodic tasks. A periodic task scheduler performing scheduling of each of the plurality of periodic tasks, a scheduling request receiver configured to receive a scheduling request of the at least one aperiodic real-time task from the system, and an excess time of a scheduling time of the plurality of periodic tasks ( And aperiodic real time task scheduler for performing scheduling of the at least one aperiodic real time task with respect to a residual time.

In this case, the periodic task scheduler may preferentially schedule a task having a small entry order in the graph structure among the plurality of periodic tasks based on the period and the execution order of each of the plurality of periodic tasks.

In addition, the periodic task scheduler repeatedly deletes a task of a vertex having an entry order of zero on a graph structure among the plurality of periodic tasks, and phase-aligns the repeatedly deleted periodic tasks according to an order of deletion, thereby improving priority. Allocate and schedule the plurality of periodic tasks in consideration of the assigned priority.

In addition, when there are a plurality of tasks of a vertex having an entry order of zero, the periodic task scheduler may compare the periods of a plurality of tasks of the vertices and delete a task having a shorter period according to the comparison result.

In addition, the aperiodic real time task scheduler determines whether the scheduling time is greater than the residual time due to the scheduling time of the plurality of periodic tasks and the execution time of the requested aperiodic real time task, and as a result of the determination, When the surplus time is greater than the execution time of the aperiodic real time task for which the scheduling is requested, the execution of the aperiodic real time task for which the scheduling is requested may be accepted.

The aperiodic real time task scheduler may assign the priority of the aperiodic real time task for which scheduling is requested to the highest level when the execution of the aperiodic real time task for which the scheduling is requested is accepted, and the threshold time of the plurality of periodic tasks. If there is a periodic task of a critical time when the deadline is imminent by the update, the periodic task that is imminent due to the deadline may be performed before the aperiodic real-time task.

The non-periodic real-time task scheduler may set the priority of the non-periodic real-time task to the lowest level and execute the periodic task that is near the deadline, in order to perform the periodic task with the deadline ahead of the aperiodic real-time task. When the execution of the periodic task that is about to be completed is finished, the priority of the aperiodic real time task may be reset to the highest level.

Scheduling algorithm according to another embodiment of the present invention is a scheduling algorithm for a system for performing a plurality of periodic tasks and at least one aperiodic real-time task, in consideration of the preceding relationship of the plurality of periodic tasks, A periodic task scheduling algorithm that performs scheduling of each of the plurality of periodic tasks, and as the scheduling request of the at least one aperiodic real-time task is received from the system, a surplus time of the scheduling time of the plurality of periodic tasks. And aperiodic real time task scheduling algorithm for performing scheduling of the at least one aperiodic real time task with respect to Time.

1 is a view for explaining the precedence of periodic tasks in a scheduling algorithm according to an embodiment of the present invention.
2 is a diagram illustrating an example of a graph structure of periodic tasks based on a neighbor list in a scheduling algorithm according to an exemplary embodiment of the present invention.
3 is an algorithm for assigning priorities to periodic tasks in a scheduling algorithm according to an embodiment of the present invention.
FIG. 4 is a view for explaining a process of assigning priority by a priority assignment algorithm shown in FIG.
5 is a diagram illustrating an example of a scheduling result by a phase alignment based priority allocation algorithm in a scheduling algorithm according to an embodiment of the present invention.
6 is a diagram illustrating a configuration of a scheduling apparatus capable of performing a scheduling method according to another embodiment of the present invention.
7 is a diagram illustrating a result scheduled by the scheduling apparatus.
FIG. 8 is a simplified view of the operation of the aperiodic real time task scheduler shown in FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The scheduling algorithm of the present invention provides an offline scheduling method for periodic tasks and an online scheduling method for aperiodic real-time tasks.

Here, the offline scheduling method is a method of scheduling periodic tasks in consideration of the prior relationship of the periodic tasks according to the priority on the offline based on the periodic and topological sort of the periodic tasks. The online scheduling method is a method of determining whether to accept an aperiodic real time task using residual time of periodic tasks scheduled by offline scheduling and assigning a priority.

Furthermore, according to an embodiment of the present invention, the scheduling algorithm may represent the periodic tasks of the same period as a set. In addition, instead of using the slack table, the scheduling algorithm of the present invention can dynamically calculate the surplus time of the periodic task by dynamically updating the parameters (period, execution time, frequency of occurrence) of the periodic task set. Accordingly, the present invention can reduce the memory waste required for the generation of the slack table, it is possible to reduce the amount of calculation than before by using a periodic task set.

According to an embodiment of the present invention, the scheduling algorithm may satisfy the fast response time of the aperiodic real time task using the threshold time of the task.

는 본 발명의 일 실시예에 따라

의 각각의 요소에 따라 그 특성이 표현될 수 있다. 여기서,

는 주기 태스크

의 수행 시간을 나타내고,

는 주기 태스크

의 주기를 나타내고,

는 우선 순위를 나타내고,

는 주기 태스크

에서 생산되는 데이터를 소비하는 태스크로 연결되는 간선들을 나타내고,

는 주기 태스크

가 사용하는 데이터를 생산하는 생산자 태스크의 집합을 나타낸다.Furthermore, the system model of the scheduling algorithm of the present invention can be implemented as follows. System model is an embodiment, the periodic task

According to one embodiment of the present invention

Depending on each element of, its characteristics can be expressed. here,

Cycle task

Represents the execution time of,

Cycle task

Represents the period of,

Indicates priority,

Cycle task

Represents edges that lead to tasks that consume data produced by

Cycle task

Represents a set of producer tasks that produce data for use.

의 집합이고, E는 시스템상의 모든 간선들

의 집합이다. The periodic relationship between the periodic task set and each periodic task may be characterized by a direct acyclic graph (DAG) having a directionality, and may be represented by G (V, E). Where V is all periodic tasks on the system

Is the set of, and E is all the edges in the system

.

1 is a view for explaining the precedence of periodic tasks in a scheduling algorithm according to an embodiment of the present invention. Periodic tasks may include a plurality of producer tasks and a plurality of consumer tasks. Here, the consumer tasks may be performed after their producer tasks are performed by the predecessor, and if the producer tasks are not performed, they may not be performed.

(105)는 소비자 태스크로서,

(105)의 생산자 태스크들인

(102) 및

(103)이 모두 수행되어야, 자신의 태스크가 수행될 수 있다. Referring to FIG. 1, for example

105 is a consumer task,

Producer tasks of 105

102 and

Once all of 103 has been performed, its task can be performed.

In order to satisfy the synchronization constraints on the sampling of periodic tasks in this relationship between the producer and the consumer, the period of each periodic task may be assigned to have a harmonic relationship. Here, the synchronization constraint means a constraint that the consumer task must use the data of the producer task in its own cycle. Thus, the scheduling algorithm can, by way of example, set the period of the consumer task to be an integer multiple of the producer's task period, thereby enabling the consumer task to use more of the producer's data produced in its own cycle.

로 표현하고, 우선 순위를 가지는 비주기 실시간 태스크를

로 표현할 수 있다. 본 발명에서 사용되는 비주기 실시간 태스크는 다른 비주기 실시간 태스크와 동시에 발생하지 않으며, 이전에 발생된 비주기 실시간 태스크의 수행이 종료된 후에 다음 비주기 실시간 태스크가 처리되는 것을 가정하도록 한다.
The system model of the present invention can represent aperiodic real-time task occurring at an unspecified time t as A (t). In addition, the system model of the present invention provides aperiodic real-time tasks with execution time.

Aperiodic real-time tasks with priorities

. The aperiodic real time task used in the present invention does not occur simultaneously with other aperiodic real time tasks, and assumes that the next aperiodic real time task is processed after the execution of the previously generated aperiodic real time task is finished.

The offline scheduling method of the scheduling algorithm of the present invention may be performed based on a topological sort as an embodiment. Here, phase alignment refers to listing all vertices without violating the preceding order of each vertex present in the graph.

Algorithms related to phase alignment generally select a vertex with an input degree of zero and delete all edges connected to the selected vertex. The algorithm related to phase alignment then repeats this selection and deletion operations, ending the algorithm when all vertices are selected and their edges are deleted. In the algorithm related to the phase alignment, the phase alignment is performed in the order of deletion by these iterations. The scheduling algorithm of the present invention may use a neighbor list to take advantage of such phase alignment.

1. Periodic task scheduling algorithm

2 is a diagram illustrating an example of a graph structure of periodic tasks based on a neighbor list in a scheduling algorithm according to an embodiment of the present invention.

Referring to FIG. 2, each of the periodic tasks 201 to 206 has an address of a consumer task using its data as an adjacent node, and indicates the number and period of producer tasks producing its entry order, i.e., the data to use. It can have as an element.

는 소비자 태스크들

및

의 주소를 인접 노드로서 가지고, 값이 0인 진입 차수

를 가지고, 값이 50인 주기

를 요소로서 가지고 있다.For example, periodic task

Consumer tasks

And

Entry order with the address of as 0 and having a value of 0

With a value of 50

Has as element

The phase alignment algorithm of the periodic task graph uses a general phase alignment algorithm, but a method of comparing the periods of the corresponding periodic tasks may be added to the selection of the periodic task whose entry order (number of producer tasks) is zero.

3 illustrates an algorithm for assigning priorities to periodic tasks in a scheduling algorithm according to an embodiment of the present invention. In the above embodiment, periodic tasks may be stored in a First In First Service (FIFS) queue structure.

Referring to FIG. 3, in the priority allocation algorithm, Ls is a list for comparing periods of periodic tasks having an entry order of 0, and Lp is a list in which periodic tasks are stored.

By the priority allocation algorithm, the periodic tasks can be sorted in order of decreasing order, and the sorted periodic tasks can be assigned to each priority and stored in the FIFS.

FIG. 4 is a diagram for describing a process of assigning priority by a priority assignment algorithm shown in FIG. 3.

Referring to FIG. 4, as the phase alignment based priority allocation algorithm of the scheduling algorithm according to an embodiment of the present invention is performed based on Table 1 below, the priority allocation algorithm of FIG. 3 is given priority to periodic tasks. You can see the process of granting.

[Table 1]

가 제거된 상태(410),

가 제거된 상태(420),

가 제거된 상태(430),

가 제거된 상태(440),

가 제거된 상태(450) 등으로 변경될 것이다.First, the phase alignment based priority allocation algorithm sequentially deletes vertices of entry order zero from the periodic tasks of the graph structure of the initial state 400 shown in FIG. Due to the deletion of the graph structure in the initial state (400),

Is removed (410),

Is removed (420),

Is removed (430),

Is removed (440),

Will be changed to the removed state 450 or the like.

The priority assignment algorithm may prioritize periodic tasks in the order in which they are deleted. As a result, the tasks given priority may be shown in Table 2 below.

[Table 2]

는 각 주기 태스크들이 도 4에서 삭제된 순서대로 부여된 것을 볼 수 있다. Where the priority given above

It can be seen that the periodic tasks are assigned in the order of deletion in FIG.

5 is a diagram illustrating an example of a scheduling result by a phase alignment based priority allocation algorithm in a scheduling algorithm according to an embodiment of the present invention.

Referring to FIG. 5, each periodic task may be performed without violating its own period, according to the priority assigned by the scheduling algorithm. In particular, as in the case of 500 and 510, it can be seen that the task can be performed even if the initial starting time of the periodic tasks is not set or different, while satisfying the preceding relationship between the periodic tasks.

2. Aperiodic  Real-time task scheduling algorithm

Meanwhile, the scheduling algorithm of the present invention may schedule an aperiodic real-time task arriving from online based on the priority given to the periodic tasks by the phase alignment based priority allocation algorithm described above. Such aperiodic real-time task scheduling calculates the hyper period of the periodic task first, and executes the aperiodic real-time task at the residual time remaining after the periodic task is performed within the calculated transcendental period. Can accept and control

In addition, the aperiodic real time task scheduling algorithm may assign the priority of the aperiodic real time task to the highest level until there is no periodic task at a threshold time in order to minimize the response time of the aperiodic real time task.

The transcendental period may be the least common multiple of all periodic tasks belonging to the system of the present invention. In particular, the transcendental period may be expressed through Equation 1 below.

[Equation 1]

는 주기 태스크들의 주기들이며, LCM은 최소 공배수(Least Common Multiple)이다.Where H is the transcendental cycle,

Is the periods of the periodic tasks, and LCM is the least common multiple.

Meanwhile, the phase alignment based priority allocation algorithm of the present invention sorts the periodic tasks in the order of the period size as described above. Thus, periodic tasks of the same period will be performed continuously.

Accordingly, in the present invention, it is possible to save the calculation time before performing the periodic task by defining the periodic tasks of the same period as a group (group). In the present invention, periodic tasks of the same period may be referred to as Sj.

에 따른 각 요소들을 가질 수 있다. 본 발명에서 상기의 요소는 Xj로 표시하도록 하며, 그 X에는

의 각 요소들이 될 수 있다.In the present invention, the periodic tasks Sj of the same period are

Each element may be in accordance with. In the present invention, the above element is represented by Xj, and X is

Each element can be

는 주기 태스크들 Sj에 속하는 주기 태스크들 각각의 주기이다. Nj는 초월 주기 H 안에서 주기 태스크들 Sj이 발생하는 횟수로서 아래의 수학식 3을 통해 계산될 수 있다.

Is a period of each of the periodic tasks belonging to the periodic tasks Sj. Nj is the number of times periodic tasks Sj occur in the transcendental period H and may be calculated by Equation 3 below.

&Quot; (3) "

는 초월 주기의 시작 시간이다. 상기의 횟수 Nj는 주기 태스크들 Sj의 주기가 끝나는 시점에서 1이 감소될 수 있다. 또한, 주기 태스크들 Sj의 수행 시간의 합은

로서 아래의 수학식 4를 통해 계산될 수 있다.here,

Is the start time of the transcendental cycle. The number Nj may be decreased by 1 at the end of the period of the periodic tasks Sj. Also, the sum of the execution times of the periodic tasks Sj is

It can be calculated through Equation 4 below.

&Quot; (4) "

In addition, the time at which tasks belonging to the periodic tasks Sj have been performed so far is Pj, which can be calculated through Equation 5 below.

&Quot; (5) "

는 Sj의 주기 시작 시간에 t까지의 수행 시간을 의미한다.At this time,

Denotes the execution time up to t at the start time of the cycle of Sj.

Meanwhile, Cj is a critical time, and Sj represents a value up to an initial threshold time after the start of its cycle. Here, the threshold time is a boundary time at which the periodic task may be performed while satisfying its period. If a periodic task exceeds its threshold time, it is out of its own cycle.

는 비주기 실시간 태스크가 온라인으로부터 도착하거나 또는 자신보다 우선 순위가 높은 주기 태스크에 의해 선점이 발생한 경우, 재산출되는 임계 시간이다. 상기의

은 비주기 실시간 태스크의 도착이 일어나지 않거나 선점이 발생하지 않으면, Cj값과 동일할수 있다. 따라서, 시간 t에 비주기 실시간 태스크가 도착하거나 우선 순위가 높은 주기 태스크에 의한 선점이 발생한 경우, 아래의 수학식 6을 이용하여

을 갱신할 수 있다.This threshold time Cj may be calculated as in the method for generating an idle time table in the EDL algorithm. Especially,

Is the threshold time that is recalculated if the aperiodic real-time task arrives online or is preempted by a periodic task that is higher than itself. The above

May be equal to the Cj value if no arrival of the aperiodic real-time task occurs or no preemption occurs. Therefore, when the non-periodic real-time task arrives at time t or the preemption occurs due to the high priority periodic task, Equation 6 below is used.

Can be updated.

&Quot; (6) "

의 갱신 이후, 자신의 Cj보다 빠른

을 가지는 Sk의

값도 다시 갱신할 필요가 있다. 그 갱신 과정은 아래의 수학식 7을 이용할 수 있다.Furthermore,

Since its renewal, faster than their Cj

Of Sk

You also need to update the value again. The update process may use Equation 7 below.

[Equation 7]

The real-time aperiodic real time task scheduling algorithm of the present invention calculates the surplus time remaining after the execution of the periodic task at time t to verify acceptance of the aperiodic real time task arriving at time t. If the surplus time is expressed as R (t), the real-time aperiodic real-time task scheduling algorithm is an embodiment, and the surplus time R (t) can be obtained using Equation 8 below.

[Equation 8]

Furthermore, the real-time aperiodic real time task scheduling algorithm may accept whether or not to execute the aperiodic real time task A (t) arriving at time t according to the condition of Equation 9 below. That is, the real-time aperiodic real-time task scheduling algorithm may selectively perform the arrived aperiodic real-time task A (t) based on the non-period real-time task A (t) arriving from online according to Equation 9 below. Can be.

&Quot; (9) "

FIG. 6 is a diagram illustrating a configuration of a scheduling apparatus capable of performing a scheduling method according to another embodiment of the present invention, and FIG. 7 is a diagram illustrating a result scheduled by the scheduling apparatus. The scheduling apparatus is a scheduling apparatus for a system that performs a plurality of periodic tasks and at least one aperiodic real-time task.

Referring to FIG. 6, the scheduling apparatus 600 includes a periodic task scheduler 610, a scheduling request receiver 620, and an aperiodic real time task scheduler 630.

The periodic task scheduler 610 performs scheduling of each of the plurality of periodic tasks in consideration of a preceding relationship between the plurality of periodic tasks. Here, the periodic task scheduler 610 performs scheduling of the plurality of periodic tasks based on the phase alignment based priority assignment algorithm described above.

The scheduling request receiver 620 receives a scheduling request of an aperiodic real time task transmitted by the system.

The aperiodic real time task scheduler 630 performs scheduling of the at least one aperiodic real time task with respect to a residual time of the scheduling time of the plurality of periodic tasks.

The aperiodic real time task scheduler 630 performs scheduling of the aperiodic real time task requested by the system based on the aperiodic real time task scheduling algorithm described above.

In particular, the operation of the aperiodic real time task scheduler 630 can be simplified as shown in FIG. 8. Referring to FIG. 8, it can be seen that the data 800 briefly describes an aperiodic real-time task scheduling algorithm.

Here, when the aperiodic real time task arrives at time t, the scheduling request receiver 620 receives a scheduling request for the aperiodic real time task at time t from the system, and the aperiodic real time task arrives at time t. If not, it means that the scheduling request receiver 620 did not receive the scheduling request.

Accordingly, the aperiodic real time task scheduler 630 may schedule the aperiodic real time task based on the aperiodic real time task scheduling algorithm when the aperiodic real time task arrives at time t.

Looking at the operation of the aperiodic real time task scheduler 630 in detail, the aperiodic real time task scheduler 630 uses the condition of Equation 9 to determine the scheduleability of the aperiodic real time task requested by the system. Check it. That is, the aperiodic real time task scheduler 630 may determine whether to execute the aperiodic real time task according to whether the condition of Equation 9 is established.

That is, if the condition of Equation 9 is not satisfied, the aperiodic real time task scheduler 630 does not accept the execution of the aperiodic real time task A (t). On the other hand, if the condition of Equation 9 is satisfied, the aperiodic real time task scheduler 630 accepts the execution of the aperiodic real time task A (t).

When the execution of the aperiodic real time task A (t) is accepted, the aperiodic real time task scheduler 630 assigns the priority of the aperiodic real time task A (t) to the highest level when the scheduling check passes, and responds. You can make time faster.

를 갱신하고, 우선 순위에 따른 주기 및 비주기 태스크를 수행할 수 있다.In addition, the aperiodic real time task scheduler 630 may be configured to perform periodic tasks.

It can update and perform periodic and aperiodic tasks according to the priority.

가 임박한 주기 태스크가 있으면, 비주기 실시간 태스크 A(t)의 우선 순위를 최하위로 할당할 수 있다. 이는

가 임박한 주기 태스크를 먼저 실행하기 위함이다. 그리고, 비주기 실시간 태스크 스케줄러(630)는

가 임박한 주기 태스크의 수행이 끝나면, 비주기 실시간 태스크 A(t)의 우선 순위를 최상위로 다시 할당할 수 있다.In addition, the aperiodic real time task scheduler 630

If there is an impending periodic task, the priority of the non-periodic real-time task A (t) may be assigned to the lowest. this is

This is to execute the impending cycle task first. In addition, the aperiodic real time task scheduler 630

After the execution of the impending periodic task, the priority of the non-periodic real-time task A (t) may be reassigned to the highest level.

Accordingly, the non-periodic real-time task scheduler 630 sets the priority of the non-periodic real-time task to the lowest level when there is a periodic task that has a critical time imminent, until the end of the execution of the periodic task whose critical time is imminent. Can delay the performance of.

를 이용하면 아래의 표 3과 같은 태스크 집합이 나올 수 있다.On the other hand, a set of tasks at time 110 using the aforementioned tasks of Table 2

If you use, you can get a task set as shown in Table 3 below.

[Table 3]

If R (t) is obtained when the aperiodic real-time task A with the execution time of 30 arrives at time 110, it is 30, and the execution time of A is equal to R (t), so that scheduling of A (t) is possible. Therefore, the value of S1 can be updated to 135 as shown in Table 4 below and online scheduling can be performed.

[Table 4]

및

의 주기를 보장하기 위하여 우선순위가 최하위로 할당된다. 이에 따라, 실시간 비주기 태스크 A의 수행이 지연되고, 주기 태스크들

및

가 수행할 수 있다. 이후,

및

의 수행외 남은 시간에서 실시간 비주기 태스크 A가 수행될 수 있음을 볼 수 있다.Referring to FIG. 7, at time 135, the real-time aperiodic task A is assigned to the group S1 where the threshold time is imminent.

And

Priorities are assigned at the lowest to ensure a period of. Accordingly, the performance of the real-time aperiodic task A is delayed, and the periodic tasks

And

Can be done. after,

And

It can be seen that the real-time aperiodic task A can be performed at the remaining time other than that of.

On the other hand, Figure 9 shows a method of performing a scheduling algorithm according to another embodiment of the present invention. In operation 900, the scheduling of each of the plurality of periodic tasks may be performed in consideration of a preceding relationship between the plurality of periodic tasks. In operation 910, the method may determine whether scheduling of the at least one aperiodic real-time task is requested from the system.

If it is determined in step 910 that the scheduling of the at least one aperiodic real-time task is requested, the method may include the at least one of the residual time of the scheduling time of the plurality of periodic tasks in step 920. Scheduling of aperiodic real-time tasks can be performed.

In step 930, the method performs the periodic task and the non-periodic task in order according to the priority, as a result of the scheduling in step 920.

On the other hand, if it is determined in step 910 that the scheduling of the at least one aperiodic real-time task is not requested, the method will perform the periodic tasks scheduled in step 900 according to their respective priorities.

The methods according to embodiments of the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the equivalents of the claims, as well as the claims.

Claims (15)

A method of performing a scheduling algorithm in a system for performing a plurality of periodic tasks and at least one aperiodic real-time task for processing an event occurring at an unspecified time,
Performing scheduling of each of the plurality of periodic tasks in consideration of a preceding relationship between the plurality of periodic tasks; And
If scheduling of the at least one aperiodic real time task is requested from the system, performing scheduling of the at least one aperiodic real time task with respect to a residual time of a scheduling time of the plurality of periodic tasks
Lt; / RTI >
The scheduling of the at least one aperiodic real time task may include:
Computing a Hyper Period of the plurality of periodic tasks first, and after the plurality of periodic tasks are performed within the calculated transcendental period, accept the execution of the at least one aperiodic real-time task at the surplus time And steps to control
Scheduling algorithm performing method comprising a. The method of claim 1,
Performing scheduling of each of the plurality of periodic tasks
Based on a period and an execution order of each of the plurality of periodic tasks, preferentially scheduling a task having a low entry order on a graph structure among the plurality of periodic tasks;
How to perform a scheduling algorithm. 3. The method of claim 2,
Performing scheduling of each of the plurality of periodic tasks
Repeatedly deleting a task of a vertex having an entry order of zero on a graph structure among the plurality of periodic tasks;
Phase-aligning the repeatedly deleted periodic tasks according to a deletion order and assigning priorities; And
Performing scheduling of the plurality of periodic tasks in consideration of the assigned priority;
Scheduling algorithm performing method comprising a. The method of claim 3,
When there are a plurality of tasks of vertices having the order of zero,
Iteratively deleting the task of the vertex of the entry order is 0
Comparing periods of a plurality of tasks of the vertices, and first deleting a task having a shorter period according to the comparison result
How to perform a scheduling algorithm. The method of claim 1,
Accepting execution of the scheduled aperiodic real-time task according to the residual time by the scheduling time of the plurality of periodic tasks and whether the scheduling is greater than the execution time of the requested aperiodic real-time task. step
A scheduling algorithm performing method further comprising. The method of claim 5,
If the execution of the aperiodic realtime task for which the scheduling is requested is accepted, allocating a priority of the aperiodic realtime task for which the scheduling is requested to the highest level;
Updating a threshold time of the plurality of periodic tasks;
If there is a periodic task of a critical time that the deadline is imminent due to the update, performing the periodic task of which the deadline is imminent before the aperiodic real-time task
A scheduling algorithm performing method further comprising. The method according to claim 6,
The step of performing the periodic task near the end of the non-periodic real-time task is
Setting a priority of the aperiodic real-time task to the lowest level;
Executing a periodic task in which the deadline is imminent; And
Resetting the priority of the non-periodic real-time task to the highest level after executing the periodic task that is about to finish.
Scheduling algorithm performing method comprising a. A scheduling apparatus in a system for performing a plurality of periodic tasks and at least one aperiodic real-time task for processing an event occurring at an unspecified time,
A periodic task scheduler configured to perform scheduling of each of the plurality of periodic tasks in consideration of a preceding relationship between the plurality of periodic tasks;
A scheduling request receiver configured to receive a scheduling request of the at least one aperiodic real time task from the system;
Aperiodic real time task scheduler for performing scheduling of the at least one aperiodic real time task with respect to a residual time of the scheduling time of the plurality of periodic tasks.
Lt; / RTI >
The aperiodic real time task scheduler,
The periodic period of the plurality of periodic tasks is calculated by the periodic task scheduler first, and after the plurality of periodic tasks are performed within the calculated transcendental period, the at least one aperiodic at the surplus time. Scheduling device that accepts and controls the execution of real-time tasks. 9. The method of claim 8,
The periodic task scheduler
Based on a period and an execution order of each of the plurality of periodic tasks, preferentially scheduling a task having a low entry order on a graph structure among the plurality of periodic tasks;
Scheduling device. 10. The method of claim 9,
The periodic task scheduler
Among the plurality of periodic tasks, a task of a vertex having an entry order of 0 is repeatedly deleted on a graph structure, and the repeatedly deleted periodic tasks are phase-aligned according to the deletion order, the priority is assigned, and the assigned priority is assigned. In consideration of a rank, the scheduling of the plurality of periodic tasks is performed.
. The method of claim 10,
When there are a plurality of tasks of vertices having the order of zero,
The periodic task scheduler
Comparing periods of a plurality of tasks of the vertices, and first deleting a task having a shorter period according to the comparison result
Scheduling device. 9. The method of claim 8,
The aperiodic real time task scheduler
It is determined whether the residual time by the scheduling time of the plurality of periodic tasks and whether the scheduling is greater than the execution time of the requested aperiodic real-time task, and as a result of the determination, the surplus time is Accepting execution of the requested aperiodic realtime task if the scheduling is greater than the execution time of the aperiodic realtime task
Scheduling device. The method of claim 12,
The aperiodic real time task scheduler
If the execution of the non-periodic real-time task for which the scheduling is requested is accepted, assign the priority of the non-periodic real-time task for which the scheduling is requested, update the threshold time of the plurality of periodic tasks, and close by the update. If there is a periodic task of this impending threshold time, performing the periodic task of which the deadline is imminent before the aperiodic real time task
Scheduling device. The method of claim 13,
The aperiodic real time task scheduler
In order to perform the periodic task near the deadline before the aperiodic real-time task, the priority of the non-periodic real-time task is set to the lowest level, the periodic task near the deadline is executed, and the periodic task near the deadline is executed. After this, to reset the priority of the aperiodic real-time task to the highest level
Scheduling device. delete

Images