IBM’s VM BY ANIRUDDHA MARATHE (CS-550/SECTION 1)

INTRODUCTION IBM’sVM (Virtual Machine) has long been recognized as a robust computing platform, spanning the entire family of S/390 and zSeries servers. Virtual Machine operating system (VM for short) is used around the world by over nine million people. For example It is also used at MIT to run some of their "mission critical" applications. The latest version of this technology is known as z/VM and supports virtual machines on IBM's z Series 900 platform (formerly known as S/390).

INTRODUCTION VM is a modern time-sharing system running at a no.of sites around the world. It is based on the concept of Virtual Machines; each VM user works in an environment which simulates (hence the term 'virtual'), and provides the full power of a System 390/VM ((hence the term 'machine' ). VM users also have powerful advanced software development tools available, such as the ReXX scripting language, the CMS Pipes facility, and the DB2/VM database system. Like most other operating systems, IBM's VM operating system offers a virtual machine to each user process. The difference between IBM's VM system and the vast majority of its competitors is that the virtual machine.

Memory management concept VM offers to a user process that has identical semantics to the machine on which VM runs, except, of course, that it is a bit slower and has fewer resources. In order to offer this, VM relies on a memory management unit in order to virtualize memory, and it relies on the fact that a program's access to non-memory resources outside the CPU is through privileged instructions, such that attempts to use these in user mode cause a trap.

Virtual Machine Monitor (VMM): Virtual Machine Monitor (VMM): software that manages the machine’s real resource among VMs. APPLCATIONS O/S VIRTUAL MACHINE O/S VIRTUAL MACHINE VMM PHYSICAL MACHINE Non- privileged instruction Protection/isol ation Privileged instruction

VMM In typical mainframe, VMM runs on top of h/w in privileged mode, and VMs runs in user mode If OS/VM issues a non-privileged instruction, they are passed down directly If OS/VM issues a privileged inst, it will cause a trap or interrupt or exception. “sensitive” inst: affect other OS/VM, so they cannot be executed by OS directly. Ex: PushF, PopF, SIDT, SLDT. To be “fully” virtualized, all sensitive and privileged instructions must be able to trapped. Intel Pentium CPU has 17 sensitive and non-privileged instructions.

The Process Model Virtual time: The time used by just this processes. Generally Virtual time progresses at a rate independent of other processes. Actually, this is false, the virtual time is typically incremented a little during systems calls used for process switching; so if there are more other processors more ``overhead'' virtual time occurs. Virtual memory: The memory as viewed by the process. Each process typically believes it has a contiguous chunk of memory starting at location zero. Of course this can't be true of all processes (or they would be using the same memory) and in modern systems it is actually true of no processes (the memory assigned is not contiguous and does not include location zero). Virtual time and virtual memory are examples of abstractions provided by the operating system to the user processes.

Advantages. Some advantages of using virtual machines include:  Portability  Added Security  Useful for developing O/S and  Reliability  System development can be done on the virtual machine, instead of on a physical machine  A perfect vehicle for operating-systems research and development

Disadvantages Difficult to implement due to the effort required to provide an exact duplicate to the underlying machine The isolation, however, permits no direct sharing of resources The main disadvantage of this approach is reduced efficiency. provides complete protection of system resources since each virtual machine is isolated from all other virtual machines.

JVM Compiled Java programs are platform-neutral bytecodes executed by a Java Virtual Machine (JVM). JVM consists of - class loader - class verifier - runtime interpreter Just-In-Time(JIT) compilers increase performance.

Reasons for Linux to run on VM Running the Linux operating system as a guest of z/VM or VM/ESA is a smart choice. Consider the following benefits VM offers a Linux guest environment: Resources can be shared among multiple Linux images running on the same VM system. These resources include: CPU cycles, memory, storage devices, and network adapters. Server hardware consolidation -- running tens or hundreds of Linux systems on a single zSeries offers customers savings in space and personnel required to manage real hardware. Virtualization -- the virtual machine environment is highly flexible and adaptable. New Linux guests can be added to a VM system quickly and easily without requiring dedicated resources. This is useful for replicating servers in addition to giving users a highly flexible test environment.

Continued Running Linux on VM means the Linux guest(s) can transparently take advantage of VM support for zSeries hardware architecture and RAS features. VM/ESA provides high-performance communication among virtual machines running Linux and other operating systems on the same processor. The underlying technologies enabling high-speed TCP/IP connections are virtual channel-to-channel (CTC) adapter support and VM IUCV (Inter-User Communication Vehicle). Linux on zSeries includes a minidisk device driver that can access all DASD types supported by z/VM and VM/ESA. Data-in-memory performance boosts are offered by VM exploitation of the z/Architecture. Debugging -- VM offers a functionally rich debug environment that is particularly valuable for diagnosing problems in the Linux kernel and device drivers.

Backups and Cache Backups cease to be an issue; because VM is managing all the disks for the virtual machines, all their data is backed up with the VM backup. The same with data integrity; for that kind of cash, you get well-implemented hot-swappable RAID. VM has an extremely efficient cache. Frequently accessed disk blocks will be held in the cache and requests never go to the drives at all. This is a huge win if you either share disks among machines, or if you're running a server form.