ProcessA process is an instance of an application. Each process has its own independent execution context and resources, such as a virtual address space. Practical operating systems provide the execution context as a separate concept called a "thread". For simplicity, in this book we'll treat each process as having a single thread.   Process control block The following process structure defines ..

4.2 Process StateEvery process in the system is assigned a unique identifier termed the process identifier (PID). PIDs are the common mechanism used by applications and by the kernel to reference processes. PIDs are used by applications when the latter send a signal to a process and when receiving the exit status from a deceased process. Two PIDs are of special importance to each process: the PI..

Part II: ProcessesChapter 4.1 Introduction to Process ManagementA process is a program in execution. (프로세스의 정의. 정확하게 따지자면, 프로그램과는 구분된다.)A process has an address space containing a mapping of its program’s object code and global variables. It also has a set of kernel resources that it can name and on which it can operate using system calls. These resources include its credentials, signal state, a..

3.6 Timing ServicesThe kernel provides several different timing services to processes. These services include timers that run in real time and timers that run only while a process is executing.   Real TimeThe system’s time offset since January 1, 1970, Universal Coordinated Time (UTC), also known as the Epoch, is returned by the system call gettimeofday. (협정 세계시) Most modern processors (includin..

3.4 Clock InterruptsThe system is driven by a clock that interrupts at regular intervals. Each interrupt is referred to as a tick. On the PC, the clock ticks 1000 times per second. At each tick, the system updates the current time of day as well as user-process and system timers.  Handling 1000 interrupts per second can be time consuming. To reduce the interrupt load, the kernel computes the num..

3.2 System CallsThe most frequent trap into the kernel (after clock processing) is a request to do a system call. System performance requires that the kernel minimize the overhead in fielding and dispatching a system call. The system-call handler must do the following work:Verify that the parameters to the system call are located at a valid user address, and copy them from the user’s address spa..

2.5 Security The FreeBSD security model has been developed over 40 years of evolving application needs. The key insight is that security must be part of system design; it cannot be successfully added later. The model addresses many different goals:Support authenticated local and remote access by multiple users, as well as integration with distributed authentication and directory servicesAllow us..

Kernel Services The boundary between the kernel- and user-level code is enforced by hardware-protection facilities provided by the underlying hardware. The kernel operates in a separate address space that is inaccessible to user processes. Privileged operations—such as starting I/O and halting the central processing unit (CPU)—are available to only the kernel. Applications request services from ..

8. Transport layer 1 - 3계층이 컴퓨터는 찾았고, 4계층은 destination software를 찾는 과정 (process to process) - 한 프로세스에서 다른 프로세스로 packet을 전달하기 위하여 - 가장 유명한 것은 클라이언트 / 서버 구조 / 컴퓨터 2대의 통신 - 본인이 요청할 때, 내가 local host / 상대편이 remote host + 컴퓨터 안의 소프트웨어, process를 지칭하게 됨 -> local process & remote process - Port number – 호스트 운영체제 위에서 돌아가는 다양한 프로세스, 프로그램을 식별하는 번호 (16 bit int) + 많이 사용하는 표준 SW 프로그램은 미리 1024개 지정 -> 이외의 값은 임의로..

CFS Completely Fair Process Scheduling in Linux