KR0164139B1 - Method of nanagement of ready queue for enhancing o.s real-time - Google Patents

Abstract

The present invention relates to a method of managing a ready queue for improving real-time of an operating system, and more particularly, to a method applicable to a ready queue management of an operating system having a priority-based scheduling scheme. will be. Therefore, the context switching time, which greatly affects the performance of the operating system, is performed more efficiently and within a fixed time, so that the operation scheduler of the operating system finds the task having the highest priority in connection cost ◎ (1). This is very useful because the operating system can be applied to the management of various resources by improving the real-time performance of the operating system.

Description

Ready Queue Management Method to Enhance Real Time of Operating System

1 is a schematic diagram showing the type of a general ready queue management method.

(a) is a schematic diagram showing the type of the task with priority p connected to the pth ready queue element,

(b) is a schematic diagram showing the types of tasks connected in order of priority to a single queue element.

2 is a flowchart illustrating a method of managing a ready queue for improving real time of an operating system of the present invention.

(a) is a flowchart showing the case of insertion,

(b) is a flowchart showing a case of finding,

(c) is a flowchart showing the case of deletion.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for managing a ready queue for improving real-time performance of an operating system. In particular, the present invention is a method applicable to a ready queue management of an operating system having a priority-based scheduling scheme.

Therefore, Context Switching time, which greatly affects the performance of the operating system, can be performed more efficiently and within a fixed time, and it is very useful because it can be applied to management of various resources managed by the operating system.

As is known, in the operating system, a scheduler divides the available time of processors in each process, thereby creating a process for a task to be executed and preparing the ready state. It allocates one processor's allocation time to prevent one processor from monopolizing the system.

A queue is also a group or queue of things waiting to be processed by the processor. It is usually contained in main memory and connected to each other by address assignment.

On the other hand, the existing operating system ready queue management method having priority-based scheduling method is largely divided into two types.

Referring to the drawings, a schematic diagram showing the type of a general ready queue management method can be shown as shown in FIG.

In the case of (a), the task corresponding to each priority address (queue element) can input and output information to L ready queues from low priority 0 to high priority (L-1). It is organically connected.

A task with priority p is always connected to the pth ready queue element. Since the tasks connected to each queue element are managed in First In First Out (FIFO), the connection cost is (1). When a task that is currently running is removed from a ready queue by an event, it must find the queue element to which the first task is connected, starting with the L-1th queue element. That is, the cost of ((L) is consumed to find the task having the highest priority.

Unlike the method of (a), (b) manages a queue element differently from the method of (a). Since the tasks connected to this queue are connected in order of priority, the highest priority task is located at the front of the queue. You can find this task at the cost of (1). However, in the case of concatenation, since the sort operation is necessary, if the total number of tasks in the current system is N, in the worst case, there is a disadvantage that a consolidation cost of (N) is required.

Each task having the above characteristics is represented by '◎', and each task priority is indicated at the top of the corresponding?.

In addition, as shown in (b), the priority relationship of tasks means that p1≥p2≥p3.

The present invention is characterized in that it is possible to implement both the cost of connecting the task to the ready-to-ready and the cost of finding the highest priority task at the cost of (1) in order to solve the conventional problems as described above.

That is, a function essential to the operation sequence of the present invention is called sylos_log2 (x), and this function sylos_log2 (x) is defined as follows.

For non-negative 32-bit integer x,

In this definition, (int) is the casting of the programming language.

A software implementation of this function is shown below.

The array log2_tbl [] is a pre-calculated and stored sylos_log2 value for 256 integers from 0 to 255 for fast calculation of the function sylos_log for non-zero 32-bit integers. In other words, if the integer x is one of 0 to 255, the value of log2_tbl [x] is equal to sylos_log2 (x).

For example, the 32-bit integer x

It can be expressed as x = A * ₂₂₄ + B * 2 ₁₆ + C * 2 ₈ + D (0≤A, B, C, D256).

In other words, it is (ABCD) _{256 in} 256 digits. In this case, sylos_log2 (x) is an operation that finds the position of the most significant non-zero bit, so if A is not 0

In the form as described above, first, find the non-zero highest number among A, B, C, and D.

That is, if the non-zero most significant number is A,

Since A, B, C, and D are 8 bits, the values of sylos_log2 from 0 to 256 are calculated in advance and a data value table (table) is created and referenced.

When the position of the most significant bit (MSB) of the 32 bits is 31 and the position of the least significant bit (LSB) is 0, for the 32-bit positive integer x, sylos_log2 (x) is the most significant bit having the value of 1 out of 32 bits. Calculate the location.

For example,

sylos_log2 (Oxdeadbeef) = 31. (Where deadbeef is a hexadecimal number each), where sylos_log2 is only applicable to non-negative 32-bit integers.

This restriction can be extended to 1024 bits using an additional 32-bit metabit map. The same extension method can support more bits, but in actual applications, since 1024 is a sufficient number, the present invention contemplates limiting the maximum number of bits to 1024. 1024 bits and meta bitmap in C language,

The pth bit of the 1024 bits corresponds to the p% 32 bit (the remainder of p divided by 32) of bitmap [(int) (p / 32) .If the xth bit of the metabitmap is 0, bitmap [x] is 0 indicates that bitmap [x] is a positive integer Under this assumption, if there is at least one non-zero bit, the following calculation calculates the position p of the most significant bit of 1024 bits: You can get it.

When the priority of a task has a value from 0 to L-1 (L is higher than 0 and longer or smaller than 1024), (1) The ready queue management is first performed in the same form as in (a) of FIG. Configure and additionally set the following data structure:

The pth bit of the L bits has a value of 0 if the pth cue element is empty and 1 if one or more tasks are connected. The xth bit of meta_ready_map has the value 0 if ready-map [x] is 0, and 1 if it is not 0. And when the new task is connected to the ready queue or the task which is connected is removed from the queue, the above condition must be maintained.

In the above situation, the queue element to which the task with the highest priority is connected can be found through the following calculation.

In other words, the first task of the pth queue element is selected as the next task. Operating systems with priority scheduling schemes have the lowest priority, and simply create tasks that round infinite loops and make them ready, so sylos_log2 is unlikely to yield -1.

Reddy queue management using the sylos_log2 function includes three operations: insertion, top priority task finding, and deletion, which will be described using a flowchart.

FIG. 2 is a flowchart illustrating a method of managing a ready queue for improving real time of an operating system of the present invention, and FIG. 2A is a flowchart illustrating a case of insertion.

If you try to attach a task with priority p to the ready queue (step S1), then it is determined whether the pth ready queue is empty (step S2), and if it is not empty, the ready queue is FIFO ordered to the p ready queue. (Step S5), if empty, the quotient of p divided by 32 is x and the remainder of p divided by 32 is y (step S3), meta_ready_map to meta_ready_map, respectively. Compute and replace (0 × 1Lx), and perform step (step S4) of calculating and replacing ready_map [x]; (0x1Ly) in ready_map [x] sequentially and finally performing step S5. The operator has the same meaning as the operator used in C language programming. The mathematical meaning of 0 × 1x is the same as 2 ^x . Is the operator used in C language programming Has the same meaning as ready_map [x] (0 × 1Ly) means to perform OR operation on ready_map [x] and (0 × 1Ly). 'Means' logical ora.)

(b) is a flowchart showing the case of finding.

Let sylos_log2 (meta_ready_map) be x (step F1) and sylos_log2 (ready_map [x]) be y (step F2) to obtain the highest priority p we want to find by 32 * x + y (step F3), The CPU is allocated to the first task of the pth red queue (step F4).

(c) is a flowchart which shows the case of DELETION.

The priority of the task to be removed from the ready queue is called p (step D1), and the task is removed from the ready queue (step D2). At this time, it is determined whether the pth ready queue is empty (step D3). Otherwise, the operation is considered complete and the end of the operation. If empty, the quotient of p divided by 32 is x, the remainder of p divided by 32 is set to y (step D4), and the yth bit of ready_map [x] is set. Make it 0 (step D5), again determine if ready_map [x] is 0 (step D6), terminate the operation if it is not 0, and set the x-th bit of meta_ready_map to 0 (step D7) if it is 0 Perform.

That is, by using the sylos_log2 function and the metabit map in the above-described order, it is possible to manage the cost of the ready queue which has a great influence on the performance of the operating system.

On the other hand, the operating system must manage various hardware or software resources held by the system. Therefore, using the algorithm described in the present invention, resource management is also possible at a low memory speed.

When there are L resources of the same type (assuming L≤1024 for the sake of discussion), assign 0 to L-1 numbers to each resource and indicate the value of the allocated resource as a bit with 0. Unallocated resources are marked with a bit of value 1. The metabit map is then set to the value of each bit in the same manner as the metabit map associated with the ready queue.

If the sylos_log2 value of the meta bitmap is -1, it means that there is no free resource. If the value of sylos_log2 is 0, the free resource can be found at the cost of (1) by using the same method as in the case of ready queue. This method has the advantage of better memory efficiency than the resource management method using the existing linked list.

As described above, the present invention improves the real-time performance of the operating system by enabling the scheduler of the operating system to find the task having the highest priority at the connection cost (1).

Claims (4)

In the Ready Queue management method for improving the real-time performance of the operating system, the task is connected to the Ready Queue (insertion, deletion, finding the highest priority task). Function sylos_log2 (x) to implement the connection cost as ◎ (1) is a Ready Queue management method for improving the real-time performance of the operating system, characterized by the following equation. For non-negative 32-bit integer x, (However, (int) serves as a cast for the C programming language.) The method of claim 1, wherein the INSERT method attempts to connect a task having priority p to the heady queue (step S1), and determines whether or not the p-th ready queue is empty (step S2). If not empty, connect the ready queue to the pth ready queue in FIFO order (step S5), if empty, the quotient of p divided by 32 is x and the remainder of p divided by 32 is y (step S3), respectively. meta_ready_map Compute and replace (0x1Lx), and ready_map [x] for ready_map [x] After calculating and replacing (0x1Ly) (step S4), step S5 can be carried out sequentially to implement a ready queue (Ready Queue) management method for improving the real-time characteristics of the operating system. The method of claim 1, wherein the method of finding (FINDING) is called sylos_log2 (meta_ready_map) x (step F1), and sylos_log2 (ready_map [x]) is y (step F2), and 32 * x + y. Ready queue management method for improving the real-time of the operating system, characterized in that it can be implemented by performing the step (step F3) to obtain the task p to find. The method of claim 1, wherein the method of deleting is called priority of a task to be removed from the ready queue (step D1), and the corresponding task is removed from the ready queue (step D2). Determine if the queue is empty (step D3); if not empty, consider the deletion to be complete, end the operation; if empty, divide the p divided by 32 with x, then divide p with 32 and y After releasing (step D4), set the yth bit of ready_map [x] to 0 (step D5), again determine if ready_map [x] is 0 (step D6), if not 0, end the operation, and if it is meta_ready_map Ready queue management method for improving the real-time performance of the operating system, characterized in that it can be implemented by sequentially performing the step (step D7) to make the x-th bit of the (0).