Virtualize of IO Devices .docx
- 1. 3.6 VIRTUALIZATION OF CPU, MEMORY, AND I/O DEVICES 1. Hardware Virtualization 2. CPU Virtualization 3. Memory Virtualization 4. I/O Virtualization 5. Multi-Core ProcessorsVirtualization 1. Hardware Virtualization Modern operating systems and processors permit multiple processesto run simultaneously. If there is no protection mechanismin a processor, all instructions from different processes will access the hardware directly and cause a system crash. Therefore, all processors have at least two modes, user mode and supervisor mode, to ensure controlled accessof critical hardware. Instructions running in supervisor mode are called privileged instructions. Other instructions are unprivileged instructions. -User mode In a virtualized environment, it is more difficult to make OSes and applications run correctly. The VMware Workstationis a VM software suite for x86 and x86-64 computers. This software suiteallows users to set up multiple(x86 and x86-64 virtual computers, and to use) one or more of these VMs simultaneously. KVM can support hardware-assisted virtualization and paravirtualization by using the Intel VT-x or AMD-v respectively. 2. CPU Virtualization
- 2. Unprivileged instructionsof VMs run directly on the host machinefor higher efficiency. Critical instructionsshould be handled carefully for correctness and stability. The critical instructions are divided into three categories o privileged instructions- instructions execute in a privileged modeand will be trapped if executed outside this mode. o control-sensitive instructions - attempt to change the configuration of resources used. o behavior-sensitive instructions - have different behaviors depending on the configuration of resources, A CPU architecture is virtualizable, the ability to run the VM’s privileged and unprivileged instructions. VMM acts as a unified mediator RISC- CPU architectures can be naturally virtualized Best-Reduced Set Computer Instructions 3. Memory Virtualization Virtual memory virtualization is similar to the virtual memory support provided by modern operating systems. In a traditional execution environment, the operating system maintains mappings of virtual memory to machine memory using page tables, which is a one-stage mapping from virtual memory to machine memory. All modern x86 CPUs include a memory management unit (MMU) and a translation lookaside buffer (TLB) to optimize virtual memory performance. In avirtual memory virtualization involves sharing the physical system memory in RAM and dynamically allocating it to the physical memory of the VMs.
- 3. Two-stage mapping process should be maintained by the guest OS and the VMM, respectively: virtual memory to physical memory and physical memory to machine memory. 4. I/O Virtualization I/O virtualization involves managing the routing of I/O requestsbetween virtual devices and the shared physical hardware. At the time of this writing, there are three ways to implement I/O virtualization: full device emulation, para-virtualization, and direct I/O. Full device emulation is the first approach for I/O virtualization. Generally, this approach emulates well-known, real-world devices. 5. Virtualization in Multi-Core Processors(windows/Linux)
- 4. Virtualizing a multi-core processor is relatively more complicated than virtualizing a uni-core processor. multicore processors are claimed to have higher performance by integrating multiple processor cores in a single chip, muti-core virtualiuzation has raised some new challenges to computer architects, compiler constructors, system designers, and application programmers. first challenge, new programming models, languages, and libraries are needed to make parallel programming easier. second challenge has spawned research involving scheduling algorithms and resource management policies. The dynamic heterogeneity of hardware infrastructure mainly comes from less reliable transistors and increased complexity in using the transistors.