Lecture on High Performance Processor Architecture CS 05162

Lecture on High Performance Processor Architecture (CS 05162) Introduction to Virtual Machines An Hong han@ustc. edu. cn Fall 2007 University of Science and Technology of China Department of Computer Science and Technology CS of USTC AN Hong

Outline n System Layers, Interfaces, and VM classes n Motivations for using VMs n Virtualization n Taxonomy summary n Process VMs n System VMs n Summary n Course Introduction 2022/1/20 CS of USTC AN Hong 2

Standard System Layers n ISA − 提供硬件与软件的接口 − e. g. : Intel IA-32, MIPS, Alpha, SPARC n OS − 提供系统调用接口 − e. g. MS Windows, Linux, Solaris n Benefits − decoupled design tasks − software reuse across varying hardware configurations and generations n Starting point for all virtual machines in this course 2022/1/20 CS of USTC AN Hong 3

Disadvantages and Limitations ? n Application SW still depends on ISA and OS interfaces n OS still depends on ISA n Suboptimal performance across interfaces, get locked into interface 2022/1/20 CS of USTC AN Hong 4

Motivations for using VMs n VMs for Flexibility − Software perspective: want ability to run on all machines l reach more customers l move code between networked computers − Hardware perspective: want ability to run all programs l server consolidation(整合) l legacy applications l cross-platform software development 2022/1/20 CS of USTC AN Hong 5

Motivations for using VMs n VMs for Performance − Optimize just in time l The more you know, the more you can optimize − Isolate faults and security risks l Many server images more stable than single server − Increase utilization of resources l adjust allocations dynamically l reduce fragmentation n VMs for Multicore? 2022/1/20 CS of USTC AN Hong 6

Examples 2022/1/20 CS of USTC AN Hong 7

VM is a Computer Architecture in a broad sense 2022/1/20 CS of USTC AN Hong 8

ISA and ABI n Interface at the top − ABI (Application Binary Interface，应用二进制代码接口) − ISA (Instruction Set Architecture，指令集体系结构) − C. P. API(Application Program Interface，应用程序接口) n ISA separates hardware from rest n ABI separates processes from rest 2022/1/20 CS of USTC AN Hong 10

Taxonomy Overview n Same/different ISA at top and bottom 2022/1/20 CS of USTC AN Hong 11

Process VMs vs. System VMs n Process level VMs provide ABI to application n System VMs provide ISA to OS and applications 2022/1/20 CS of USTC AN Hong 12

VM Puzzles n (a) Emulating one instruction set with another n (b) Replicating a virtual machine so that multiple operating systems can be supported simultaneously n (c) Composing virtual machine software to form a more complex, flexible system 2022/1/20 CS of USTC AN Hong 13

Process VMs (1) n Multiprogramming − same ISA, same OS − replicates ABI so that each process thinks it has its own machine − standard in “modern” OS − can argue whether to call this a VM n Note: replication can go both ways − multiprocessor appears as single environment − clusters, grid computing 2022/1/20 CS of USTC AN Hong 14

Process VMs (2) n “Emulation” and “Dynamic Binary Translation” − OS is same, ISA is different − better known as “interpretation” and “compilation” − E. g. Digital FX!32 n Dynamic Optimizers − same OS and ISA − performance is purpose − E. g. HP Dynamo 2022/1/20 CS of USTC AN Hong 15

Process VMs (3) n High-level VMs − Use synthetic ISA l P-code l Java bytecode − Maximal platform independence l what about OS calls? − High performance penalty? l what about just-in-time compilation? 2022/1/20 CS of USTC AN Hong 16

Process VMs (4) n This combination is left out by taxonomy: − OS is different, ISA is same − for example, run Windows x 86 applications in a Linux x 86 environment (e. g. WINE) − Don’t know specific term for this VM type ? ? 2022/1/20 CS of USTC AN Hong 17

System VMs (3) n Whole System VMs − ISA is different − no ‘native’ execution possible. Complete emulation/translation required. − Usually done as a hosted VM 2022/1/20 CS of USTC AN Hong 21

System VMs (4) n Co-Designed VMs − use synthetic custom ISA at bottom − goal: reconcile diverging requirements between ISA and microarchitecture − no ‘native’ execution possible − Emulation/translation l can be joint effort by hardware and software l can be made completely transparent − E. g. Transmeta Crusoe 2022/1/20 CS of USTC AN Hong 22

Finally: VMs on top of VMs 进程虚拟机 （IA-32 ISA） 系统虚拟机 （IA-32 ISA） 协同设计虚拟机： Transmeta 的code morphing软件 2022/1/20 CS of USTC AN Hong 23

Discussion questions n Is this taxonomy good? − too broad or too narrow? − too simple or too complicated? n What VM types are most relevant? n How to implement a VM n Would a proliferation of VMs change − ABI’s? − ISA’s? − OS’s? 2022/1/20 CS of USTC AN Hong 24

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