Run Linux kernel + process scheduling primitives and creation and termination

meiyao

Run Linux kernel + process scheduling primitives and creation and termination [Copy link]

Process scheduling is a core function in the operating system. It is responsible for selecting processes to execute according to certain strategies in a single-core or multi-core processor system. In a single-core system, since only one process can use the processor at the same time, process scheduling becomes particularly important. When a process is blocked due to waiting for I/O operations, resource allocation or other reasons, the scheduler will select another ready process to execute, thereby improving the utilization of the processor.

As a general-purpose operating system, Linux needs to handle multiple types of processes, each of which has its own specific behavioral characteristics. Interactive processes focus on user experience and require a short system response time, such as text editors and browsers. Batch processes focus on throughput and can run for a long time and occupy a large amount of system resources, such as compilation tasks and database queries. Real-time processes have very strict time requirements and must be completed within a specified time, such as audio and video processing and industrial control.

From the perspective of the processor, processes can be divided into CPU-consuming and I/O-consuming processes. CPU-consuming processes need to occupy the processor for a long time for calculation, such as scientific computing, image rendering, etc. I/O-consuming processes spend most of their time waiting for I/O operations to complete, such as network requests, file reading and writing, etc. The scheduler needs to reasonably allocate processor resources according to the system load and process type to balance system throughput and responsiveness.

The Linux kernel scheduler uses a variety of strategies and techniques to optimize system performance. For example, it selects the appropriate process to execute based on factors such as process priority, I/O behavior, and running time. In addition, the scheduler also uses mechanisms such as processor cache and task queues to reduce the overhead of context switching and improve the overall performance of the system.

In the POSIX standard, the operating system-level primitives for process creation and termination do play a vital role. These primitives provide the operating system with the basic mechanism to control and manage the life cycle of a process.

In terms of process creation, the fork() function is a core primitive that is used to create a child process that is almost identical to the current process. This child process will obtain a copy of the parent process, including the parent process's code, data, heap, stack, etc. However, it should be noted that these contents are copied on write, that is, before the child process modifies these contents, they are actually pointers to the same contents of the parent process. The advantage of this is that it can improve the efficiency of process creation because there is no need to copy all the contents immediately.

The execve() family of functions is used to execute a new program in an existing process. When execve() is called, the image of the current process is replaced by the new program, and then the new program starts executing. In this way, although the process ID has not changed, the content of the process is completely different.

In terms of process termination, functions such as wait() and waitpid() are used by the parent process to wait for the child process to terminate. This is very important because when a process ends, its resources need to be reclaimed by the operating system. If the parent process does not wait for the child process to end, the child process will become a zombie process, occupying system resources but not performing any operations. In addition, the kill() function can be used to send a signal to the process to achieve forced termination of the process. The exit() function family provides a mechanism for the normal termination of the process. It will return a status code for other processes or the operating system to understand the termination status of the process.

In order to improve efficiency, the Linux operating system has expanded the fork() primitive of the POSIX standard and introduced two primitives, vfork() and clone(). vfork() is similar to fork(), but after creating a child process, it does not copy the address space of the parent process, but directly shares it. This can further improve efficiency, but there are also some limitations and precautions. clone() provides more fine-grained control and can create child processes with different attributes or capabilities.

GCC is a commonly used compiler under Linux. It compiles source code into ELF (Executable and Linkable Format) files. When we run an ELF file in Shell, Shell will create a new process to execute the program. This process involves two steps: fork() to create a child process and execve() to execute the new program.

In the Linux kernel, these process creation and termination primitives are implemented through system calls, such as sys_fork(), sys_exec(), etc. These system calls provide the kernel with an interface for interacting with user space programs, so that user space programs can request the operating system to create new processes, execute new programs, or terminate processes.

Summarize:

Process scheduling and process creation and termination are crucial functions in an operating system. Together, they ensure that the system can efficiently manage the life cycle of processes and processor resources.

Process scheduling is one of the core functions of the operating system kernel. It is responsible for selecting processes to execute according to certain strategies in a single-core or multi-core processor system. In a single-core system, since only one process can use the processor at the same time, process scheduling becomes particularly important. The scheduler improves the utilization of the processor by selecting ready processes to execute. As a general-purpose operating system, the Linux system needs to handle multiple types of processes, including interactive processes, batch processes, and real-time processes. Each process has its own specific behavioral characteristics. The scheduler needs to reasonably allocate processor resources according to the system load and process type to balance the system throughput and responsiveness.

Process creation and termination are the basic mechanisms for the operating system to control and manage the life cycle of processes. In the POSIX standard, the fork() function is used to create a child process, and the execve() family of functions is used to execute a new program in an existing process. In terms of process termination, wait(), waitpid() and other functions are used by the parent process to wait for the child process to terminate to ensure the correct recycling of resources. In addition, the kill() function and exit() family of functions provide mechanisms for forcibly terminating a process and terminating a process normally, respectively. In order to improve efficiency, the Linux operating system has expanded the fork() primitive and introduced more efficient primitives such as vfork() and clone().