Analysis of Linux process priority scheduling mechanism

Title: Analysis of Linux Process Priority Scheduling Mechanism

The Linux operating system is an open source operating system with powerful multi-tasking capabilities. In Linux systems, process scheduling is very important, which affects the performance and response speed of the system. In order to better process scheduling, the Linux system implements a process priority scheduling mechanism.

1. Process priority

In the Linux system, each process has a priority, which is used to determine the scheduling order of the process in the system. The value range of priority is usually 0~139, where 0 represents the highest priority and 139 represents the lowest priority. The priority of the process can be set by the nice value. The range of the nice value is -20~19. The smaller the value, the higher the priority.

2. Process Scheduling Strategy

Linux system adopts a variety of different process scheduling strategies. There are two common ones: real-time scheduling strategy and non-real-time scheduling strategy. Real-time scheduling strategies include FIFO scheduling and Round-Robin scheduling, and non-real-time scheduling strategies include fair scheduling and priority scheduling.

3. Process scheduling implementation

The CFS (Completely Fair Scheduler) scheduler is used in Linux systems to schedule processes. The CFS scheduler decides which process to run next based on the process's priority and VRuntime (virtual run time). Processes with smaller VRuntime will be preferred for scheduling.

4. Code Example

The following is a simple C program example that shows how to create a new process and set its priority:

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>

int main() {
    pid_t pid;
    int nice_val = 0;

    pid = fork();

    if (pid < 0) {
        perror("fork failed");
        exit(1);
    } else if (pid == 0) {
        nice_val = 5;
        printf("Child process nice value before set: %d
", nice_val);
        nice(nice_val);
        printf("Child process nice value after set: %d
", nice_val);
        printf("Child process pid: %d
", getpid());
    } else {
        nice_val = 10;
        printf("Parent process nice value before set: %d
", nice_val);
        nice(nice_val);
        printf("Parent process nice value after set: %d
", nice_val);
        printf("Parent process pid: %d
", getpid());
    }

    return 0;
}

In the above code , by calling the nice function, you can set the nice value of the process, thereby affecting the priority of the process. Different nice values ​​are set for the child process and the parent process to show the difference in process priorities.

Conclusion

Through the above analysis and code examples, we have a deeper understanding of the Linux process priority scheduling mechanism. The process priority scheduling mechanism plays a vital role in system performance and resource allocation. Understanding and mastering this mechanism is very important for system administrators and developers.

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