JPH04191935A - Task scheduling system - Google Patents

Abstract

PURPOSE:To improve the performance of a system by alternately scheduling the task of high priority and the task of low priority. CONSTITUTION:A task schedule state monitoring part 3 refers to a task schedule control table 9 every a constant period and shifts control from a priority control scheduling part 1 to a two-stage control scheduling part 5. The two-stage control scheduling part 5 classifies plural tasks into a task group with high priority and a task group with low priority and schedules the tasks of the low priority group in order by a low priority group pointer 17 of the task schedule control table 9. Then, a task schedule recovering part 7 shifts the control from the two-stage priority control scheduling part 5 to the priority control scheduling part 1 when the task finishes scheduling all the tasks of a CPU assignment queuing state. Thus, the performance of a system is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Application Field) The present invention relates to task scheduling in which a task in a multitask including a plurality of tasks uses a CPU in a time-sharing manner, tasks with high CPU
The present invention relates to a task scheduling method that improves system throughput by allowing low-priority tasks to occupy a CPU even if the CPU continues to be occupied.

(Prior art) In the conventional task scheduling method, tasks are
The task scheduler is equipped with a task ready queue in which tasks are registered in the queue in order of priority when they are in a waiting state for assignment (hereinafter referred to as ready state). The priority of the first task is compared with the priority of the task currently occupying the CPU. Schedule tasks starting from the one with the highest priority. CP the above high priority tasks
In the conventional task scheduling method, it is not easy to allocate a low priority task to the CPU.

(Problem to be Solved by the Invention) By the way, in the conventional task scheduling method, if a task with a high priority continues to occupy the CPU due to a program loop, etc., the CPU is allocated to a task with a lower priority.
There was a problem in that this resulted in a decrease in the response of the terminal and a decrease in the throughput of the entire system.

The present invention has been developed in view of the above item 1, and its purpose is to increase system throughput by allocating low priority tasks to the CPU even when high priority tasks continue to occupy the CPU. The purpose of this invention is to provide a task scheduling method that improves system performance.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention includes a plurality of tasks, and waits for the task with the lowest priority in a CPU allocation waiting state among the plurality of tasks. Scheduling monitoring means for monitoring time and CP of the scheduling monitoring means
a two-stage priority control means for classifying tasks in a U allocation waiting state into a high priority task group and a low priority task group and alternately scheduling the high priority tasks and low priority tasks; , a two-step priority control transfer means for transferring control to the two-step priority control means when the waiting time by the scheduling monitoring means exceeds a specified value; and a group of tasks with lower priority by the two-step priority control transfer means. When the task with the lowest priority among the tasks is scheduled, the two-stage priority control means schedules the task starting from the task with the highest priority.

(Operation) In the task scheduling method with the above configuration, the waiting time of the task with the lowest priority in the CPU allocation waiting state among multiple tasks is monitored, and if the waiting time exceeds a specified value, the CPU allocation is Shifts waiting tasks to control that alternately schedules tasks classified as high-priority tasks and low-priority tasks. When the task with the lowest priority among the task groups with low priority is scheduled by the schedule, the normal
Since control is shifted to scheduling from tasks with high priority, even if tasks with high priority occupy the CPU, tasks with low priority can occupy the CPU.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram schematically showing an embodiment of the task scheduling method of the present invention.

The above task scheduling method includes a priority control scheduling section 1, a task schedule status monitoring section 3.2
It includes a graded priority control scheduling section 5 and a task schedule recovery section 7.

The priority control scheduling unit 1 schedules tasks starting from the highest priority, and the task schedule status monitoring unit 3 periodically schedules tasks from the priority control scheduling unit 1 by referring to a task schedule control table 9, which will be described later. Control is transferred to the two-step control scheduling section 5. The two-stage priority control scheduling unit 5 classifies a plurality of tasks into a high-priority task group and a low-priority task group, and uses a low-priority group pointer 17 of a task schedule control table 9, which will be described later, to assign a low-priority task to a task group. Schedule group tasks one after the other.

When the task schedule recovery unit 7 finishes scheduling all the tasks in a CPU allocation waiting state (hereinafter referred to as a ready state), the task schedule recovery unit 7 transfers control from the two-stage priority control scheduling unit 5 to the priority control scheduling unit 1.

The task schedule control table 9 includes various pointers shown below, and will be explained in detail using FIG. 2.

The task schedule control table (hereinafter referred to as DAPLE) 9 includes a task schedule status flag 11 and a task schedule status change upper limit counter 3. The task schedule status flag 11 is a flag for identifying a high priority group and a low priority group of the priority control scheduling unit l and the two-stage priority control scheduling unit 5. For example, in the case of priority control, rOJ, two-stage In priority control, a high priority group is identified as "1", and a low priority group is identified as "2". The task schedule status change upper limit counter 3 is
The task schedule state monitoring unit 3 checks the unscheduled state holding counter C in the task control block provided for each of the tasks T and T-=Tn in the ready state.
2C2...Cn, it is compared with the unscheduled state holding counter Cn of the task with the lowest priority, for example, Tn. As a result of the comparison, when the value of the task schedule state change upper limit counter 13 is large, the task schedule state monitoring section 3 transfers control to the two-step priority control scheduling section 5.

The table 9 also includes a state monitoring pointer 15, a low priority group pointer 17, and a ready task control pointer 19.

The state-monitored task pointer 15 is a pointer indicating the task that caused the control to be transferred to the two-step priority control, and this task is the task scheduled at the end of the two-step priority control.

The low priority group pointer 17 is a pointer indicating a task of a low priority group of two-stage priority control.

The ready task control pointer 19 is an entry that manages tasks in the ready state in order of priority, and all tasks in the ready state are queued (task ready queue).
has been done.

Note that the task schedule status monitoring unit 3 and the like are managed by an operating system (hereinafter referred to as O8).

Next, the operation of this embodiment will be explained using the processing flowcharts of FIGS. 3 and 4.

First, FIG. 3 is a flowchart showing task status monitoring processing.

The task schedule status monitoring unit 3 is activated at regular intervals, and in the case of normal priority control, counts the unscheduled status holding counter of the lowest priority task among the tasks in the ready status, or the last task in the task ready queue. If the task has a lower priority than the task currently occupying the CPU, the process advances to step 160 (steps 100 to 1).
1o).

When the value of the unscheduled state holding counter exceeds the value of the task schedule state change upper limit counter]3, the task schedule state monitoring section 3 controls the task schedule state monitoring section 3 from the priority control scheduling section 1 to the two-stage priority control scheduling section 5.
transfer control to

On the other hand, if the value of the unscheduled state holding counter is less than or equal to the value of the task schedule state change upper limit counter 13, the process advances to step 160 (step 120).

When shifting to two-step priority control, the task schedule state monitoring unit 3 sets the state monitored task pointer 15 of table 9 to the last task in the task ready queue, and sets the low priority task group pointer 17 to the task ready queue. Set it to the first task. In addition, the task schedule status monitoring unit 3 displays a flag 1 of the task schedule status.
1 indicating two-step priority control, for example, set it to "1" and proceed to step 160 (steps 130 to 15o). When proceeding to step 160, the task schedule status monitoring H3 enters the execution waiting state and is activated again after a certain period. Then, the process returns to step 100 (step 160).

Next, task scheduling processing and recovery processing from two-stage priority control will be explained using the flowchart of FIG.

First, the task schedule status monitoring unit 3 selects the table 9.
The task scheduling status flag 11 of the CPU is checked, and in normal priority control, the priority of the task currently occupying the CPU is compared with the priority of the task at the head of the ready queue. When the priority of the task in the ready queue is high by comparison, the priority control schedule linking unit 11 schedules the task, connects the current task waiting for the right to use the CPU to the ready queue, and then assigns the right to use the CPU to the task. Perform scheduling. On the other hand, when the priority of the task occupying the CPU is high, the priority control scheduling unit 1 performs task scheduling for the task that has the right to use the CPU (steps 200 to 240).
).

When the task schedule status flag 11 in Table 9 indicates two-step priority control, the task schedule status monitoring unit 3 registers the task that has occupied the CPU up to now in the task ready queue.

After registration, the task schedule status monitoring unit 3 proceeds to step 340 when the task schedule status flag 11 indicates a high priority group, and proceeds to step 270 when it indicates a low priority group (steps 250 to 260).

Proceeding to step 270, when scheduling a task in a low priority group, the two-stage priority control scheduling unit 5 determines whether the task is the last task in the task ready queue, that is, whether all tasks in the ready state have been scheduled. Find out.

If the above-mentioned task is not the last task in the task ready queue, the two-step priority control scheduling unit 5 moves the low priority group pointer 17 to the next task in the ready queue, thereby controlling the high priority group and the low priority group. to ensure the execution of the next low priority group task. Furthermore, the two-stage priority control scheduling unit 5 changes the task schedule status flag 11 to the high priority group in order to perform the next scheduling in the high priority group (steps 270 to 300).

On the other hand, in the case of the last task in the task ready queue, the two-stage priority control scheduling unit 5 uses the wave condition monitoring pointer 15. The low priority group pointer 17 and the ready task control pointer 19 are each initialized, and control of the task schedule is transferred to the original priority control (steps 310 to 330).

When the task schedule status flag 11 indicates a high priority group (Step 340), the two-stage priority control scheduling unit 5 schedules the first high priority task and proceeds to Step 300 (Step 340).

As a result, even if a high priority task occupies the CPU, the system throughput can be improved by scheduling a low priority task.

It will also be possible to back up systems during Depack's work.

[Effects of the Invention] As explained above, according to the present invention, high-priority tasks and low-priority tasks are scheduled alternately, so even if a high-priority task continues to occupy the CPU, By allocating low-priority tasks to the CPU, system throughput can be improved and system performance can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the task scheduling method of the present invention, FIG. 2 is a diagram showing a task scheduling control table, and FIGS. 3 and 4 are flowcharts showing the operation of the present invention. 1...Priority control scheduling unit 3...Task schedule status monitoring unit 5...Two-step priority control scheduling unit 7...
Task schedule recovery unit 9...Task schedule control table]1...Task schedule status flag 13...Task schedule status change upper limit counter 17...Low priority group pointer

Claims (1)

[Claims] In a task scheduling method in which a plurality of tasks are provided and the plurality of tasks use the CPU in a time-sharing manner, the waiting time of the task with the lowest priority in a CPU allocation waiting state among the plurality of tasks is provided. A scheduling monitoring means to monitor; and classifying tasks in a CPU allocation waiting state of the scheduling monitoring means into a high priority task group and a low priority task group, and classify the high priority tasks and low priority tasks. two-stage priority control means that alternately schedules the two-stage priority control means; two-stage priority control transfer means that transfers control to the two-stage priority control means when the waiting time by the scheduling monitoring means exceeds a specified value; When the priority control transfer means schedules the lowest priority task among the low priority task group, the two-stage priority control means schedules the tasks starting from the tasks with higher priority. A task scheduling method that uses