Linux virtualization features

Article Title: describes the features of Linux virtualization. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

Virtualization has rich meanings and is widely used. ServerVirtualizationIs currently a major virtualization technology, that is, multiple independent operating systems are provided on a host computer. This article will explore the ideas behind virtualization and discuss some technologies for virtualization. We will also understand other existing Virtualization Technologies, suchLinuxVirtualization on the operating system.

Virtualization is to present something in another form. To virtualize a computer is to present the computer in the form of multiple computers or a completely different computer.

Virtualization can also combine multiple computers into one computer. This is usually called server aggregation or grid computing.

Next, let's first look at the origin of virtualization.

Virtualization history

Virtualization is not a new theme. In fact, it has been around for more than 40 years. The earliest use of virtualization technology includes the Compatible Time Sharing System developed by IBM and MIT on IBM 704) and the University of Manchester's Atlas project, one of the world's first supercomputers, are pioneers in request page scheduling and regulatory process calling.

Hardware Virtualization

IBM recognized the importance of virtualization when developing the System/Model 67 mainframe in 1960s. Model 67 virtualizes all hardware interfaces through Virtual Machine Monitor. In early computing, the operating system is called a supervisor. The operating system that can run on other operating systems is called hypervisor (this term was introduced in 1970s ).

VMM can run directly on the underlying hardware and allow multiple virtual machines (VMS) to run ). Each VM can run an instance of its own private operating System, which was called CMS (or Conversational Monitor System) earlier ). After that, the VM continues to develop. Now you can go to System z9? VM is found on the mainframe. This provides good backward compatibility, and even compatibility with the System/360 product line.

ProcessorVirtualization

Another early use of Virtualization (in this example, the simulation of the processor) is a P-code (or pseudo code) machine. P-code is a machine language that runs on virtual machines rather than hardware. As early as 1970s, P-code was well known in the Pascal System of the University of California, San Diego (UCSD). It compiled the Pascal program into P-code, then run on a P-code virtual machine. This makes the P-code program highly portable, and the P-code program can run as long as there is an available P-code virtual machine.

In 1960s, the design of BCPL (Basic Combined Programming Language) also adopted the same concept. The C Language was developed by BCPL. In this usage, the compiler will compile BCPL code into intermediate machine code called O-code. The second step is to compile the O-code into the original language of the target machine. The model used by modern compilers provides great flexibility for porting the compiler to the new target architecture (separating the frontend and backend using an intermediate language ).

Instruction Set Virtualization

The latest development in virtualization is Instruction Set virtualization or binary conversion. In this model, the virtual instruction set is converted to the Physical Instruction Set of the underlying hardware, which is usually dynamic. When the code is executed, a segment of the Code is converted. If a branch occurs, a new code set is imported and converted. This makes it very similar to the cache operation. The latter moves the instruction block from the memory to the local cache for execution.

This model was recently used in the Crusoe Central Processing Unit (CPU) designed by Transmeta. Binary Conversion is implemented by the patented Code Morphing technology. A similar example is the full virtualization solution that uses runtime code scanning to find and redirect privileged commands (to solve some problems with specific processor instruction sets ).

Virtualization type

There are more than one way to achieve virtualization. In fact, there are several methods that can achieve the same result through different levels of abstraction. This section describesLinuxCommon three virtualization methods and their advantages and disadvantages. The Industry sometimes uses different terms to describe the same virtualization method. This document uses the most common terms and provides other terms for your reference.

Hardware simulation

Undoubtedly, the most complexVirtualizationThe implementation technology is hardware simulation. In this method, you can create a hardware VM on the host system to simulate the desired hardware, as shown in 1.

Figure 1. hardware simulation VM is used to simulate the required hardware

As you can foresee, the main problem with hardware simulation is that the speed will be very slow. Since each command must be simulated on the underlying hardware, it is not uncommon to slow down the speed by 100 times. To achieve high fidelity simulation, including the cyclic precision, the simulated CPU pipeline, and cache behavior, the actual speed gap may even reach 1000 times.

Hardware simulation also has its own advantages. For example, with hardware simulation, can you run PowerPC on an arm processor host? Designed operating system without any modifications. You can even run multiple virtual machines. Each Virtual Machine simulates a different processor.

 

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