Book Image

Mastering KVM Virtualization - Second Edition

By : Vedran Dakic, Humble Devassy Chirammal, Prasad Mukhedkar, Anil Vettathu
Book Image

Mastering KVM Virtualization - Second Edition

By: Vedran Dakic, Humble Devassy Chirammal, Prasad Mukhedkar, Anil Vettathu

Overview of this book

Kernel-based Virtual Machine (KVM) enables you to virtualize your data center by transforming your Linux operating system into a powerful hypervisor that allows you to manage multiple operating systems with minimal fuss. With this book, you'll gain insights into configuring, troubleshooting, and fixing bugs in KVM virtualization and related software. This second edition of Mastering KVM Virtualization is updated to cover the latest developments in the core KVM components - libvirt and QEMU. Starting with the basics of Linux virtualization, you'll explore VM lifecycle management and migration techniques. You’ll then learn how to use SPICE and VNC protocols while creating VMs and discover best practices for using snapshots. As you progress, you'll integrate third-party tools with Ansible for automation and orchestration. You’ll also learn to scale out and monitor your environments, and will cover oVirt, OpenStack, Eucalyptus, AWS, and ELK stack. Throughout the book, you’ll find out more about tools such as Cloud-Init and Cloudbase-Init. Finally, you'll be taken through the performance tuning and troubleshooting guidelines for KVM-based virtual machines and a hypervisor. By the end of this book, you'll be well-versed with KVM virtualization and the tools and technologies needed to build and manage diverse virtualization environments.
Table of Contents (22 chapters)
1
Section 1: KVM Virtualization Basics
4
Section 2: libvirt and ovirt for Virtual Machine Management
11
Section 3: Automation, Customization, and Orchestration for KVM VMs
15
Section 4: Scalability, Monitoring, Performance Tuning, and Troubleshooting

Execution flow of vCPU

Finally, we are into the vCPU execution flow, which helps us put everything together and understand what happens under the hood.

I hope you didn't forget that the QEMU creates a POSIX thread for a vCPU of the guest and ioctl(), which is responsible for running a CPU and has KVM_RUN arg (#define KVM_RUN _IO(KVMIO, 0x80)). The vCPU thread executes ioctl(.., KVM_RUN, ...) to run the guest code. As these are POSIX threads, the Linux kernel can schedule these threads as with any other process/thread in the system.

Let's see how it all works:

Qemu-kvm User Space:
kvm_init_vcpu ()
    kvm_arch_init_vcpu()
       qemu_init_vcpu()
          qemu_kvm_start_vcpu()
             qemu_kvm_cpu_thread_fn()
    while (1) {
        ...