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Mechanism: Address Translation CPU: limited direct execution (LDE) In virtualizing memory, we will pursue efficiency and control. CRUX: How to efficiently and flexibly virtualize memory? Technique: hardware-based address translation / address translation, changing the virtual address provided by the instruction to a physical address. Interposition is powerful: On of the usual benefits of such an approach is transparency. Dynamic (Hardware-based) Relocation base and bounds / dynamic relocation: ...

Interlude: Memory API CRUX: How to allocate and manage memory in UNIX/C programs? Types of Memory stack memory: allocations and deallocations are managed implicitly by the compiler. For this reason it is sometimes called automatic memory. Declaring memory on the stack in C is easy. For example, let’s say you need some space in function func() for an integer, called x. To declare such a piece of memory, you just do something like this: 123void func() { int x;} The compiler does the res ...

The Abstraction: Address Spaces Early Systems From the perspective of memory, early machine didn’t provide much of an abstraction to users. The OS was a set of routines (a library, really) that sat in memory (starting at physical address 0, for example), and there would be one running program (a process) that currently sat in physical memory and used the rest of memory. Multiprogramming and Time Sharing multiprogramming: multiple processes were ready to run at a given time, and the OS would swit ...

Operating Systems: Three Easy Pieces We will examine a different type of scheduler known as a proportional-share scheduler, also sometimes referred to as a fair-share scheduler. An early example of proportional-share scheduling is known as lottery scheduling. The crux is how can we design a scheduler to share the CPU in a proportional manner? Basic Concept: Tickets Represent Your Share tickets: used to represent the share of a resource that a process (or user) should receive. Lottery allocate ...

Scheduling: Introduction Workload Assumptions A number of simplifying simplifying assumptions about the process running in the system, sometimes collectively called the workload. We will make the following assumptions about the processes, sometimes called jobs, that are running in the system: Each job runs for the same amount of time. All jobs arrive at the same time. Once started, each job runs to completion. All jobs only use the CPU. The run-time of each job is known. Scheduling Metrics Tur ...

Mechanism: Limited Direct Execution A few challenges: Performance Control Basic Technique: Limited Direct Execution OS: Create entry for process list. Allocate memory for program. Load program into memory. Set up stack with argc/argv. Clear registers. Execute call main(). Program: Run main(). Execute return from main. OS: Free memory of process. Remove from process list. Problem #1: Restricted Operations What if the process wishes to perform some kind of restricted operation, such a ...

Interlude: Process API The fork System Call 123456789101112131415161718192021#include <stdio.h>#include <stdlib.h>#include <unistd.h>int main(int argc, char *argvp[]) { printf("hello world (pid:%d)\n", (int) getpid()); int rc = fork(); if (rc < 0) { // fork failed fprintf(stderr, "fork failed\n"); exit(1); } else if (rc == 0) { // child (new process) printf("hello, I am child (pid:%d)", (int) getpid());  ...

Operating Systems: Three Easy Pieces The Abstraction: The Process One of the most fundamental abstractions that the OS provides to users: the process (a running program). The OS creates the illusion of nearly-endless supply of CPUs by virtualizing the CPU. The basic technique, known as time sharing （分时） of the CPU, allows users to run many concurrent processes. To implement virtualization of the CPU, and to implement it well, the OS will need both some low-level machinery and some high-level i ...

Introduction Computer Systems: Three Easy Pieces Virtualization: the OS takes a physical resource and transforms it into a more general, powerful, and easy-to-use virtual form of itself. Thus, the OS is sometimes referred to as a virtual machine. A typical OS exports a few hundred system calls that are available to applications. The OS provides a standard library to applications. The OS is sometimes known as a resource manager for CPU, memory, and disk. Virtualizing 123456789101112131415161718 ...

Seeing is believing. It used to be such a universally acknowledged viewpoint that almost all languages, eastern or western, possess similar expressions. Throughout history, this common idea has guided us and encouraged our ancestors to seek the truth, and, to some extent, it also leads to the advent of experimental science and other branches of scientific knowledge. With a deeper understanding of the world we live, people begin to doubt and challenge this proverb. Given the interest in, debate o ...