Redhat and Fedora has virtio driver ISO CD ROM images for windows and Linux in their websites. Virtio is the iommu access driver and method name to disks, NICs (ethernet) and video. Qemu-nbd is also a CLI tool which allows raw I/O access to virtual disk through network via nbd. Qemu-img is a cli tool which creates, converts, snapshots disk images. Virt-manager is VMware player like GUI as an alternative to virsh and it uses libvirt. Virsh is a toolkit which works in terminal to monitor and configure virtual machine settings. Libvirt is a library, allowing you to use python and other programming languages to configure virtual machines. SR-IOV is a chipset feature which allows splitting one PCI device to many virtual ones without performance drop via parallelized direct IO access.
#QEMU VGA SETTINGS SOFTWARE#
IOMMU is a mechanism which is part software in kernel and part hardware in chipsets, featured as VT-D (vmx) AMD-VI (svm). It also allows passing through PCI devices via vfio-pci kernel module.Īll these passthrough functionality are possible via IOMMU (Input output memory mapping unit), which maps real DMA addresses to virtualized addresses so direct access becomes possible and it brings bare-metal (native) performance. KVM is a kernel module which allows passing through CPU cores via host-passthrough without virtualizing them. Qemu is a processor emulating virtualization software with many virtual devices support (such as HDD,RAM,sound,ethernet,USB,VGA, etc.)
#QEMU VGA SETTINGS CODE#
The concurrency-if you have enough real cores-or scheduling-if not-is managed by the normal Linux scheduler, keeping code small and surprises limited.
If you want a VM with 2 or 4 cores, kvm-qemu creates 2 or 4 threads, each of them calls the KVM kernel module to start executing. One of the nice things of this architecture is that the guest code is emulated in a posix thread which you can manage with normal Linux tools. On a privileged instruction, it switches back to the KVM kernel module, which, if necessary, signals the Qemu thread to handle most of the hardware emulation. The thread calls the KVM kernel module to switch to guest mode and proceeds to execute the VM code.
The kvm-qemu executable works like normal Qemu: allocates RAM, loads the code, and instead of recompiling it, or calling KQemu, it spawns a thread (this is important). But for the foreseeable future, the Qemu team focuses on hardware emulation and portability, while KVM folks focus on the kernel module (sometimes moving small parts of the emulation there, if it improves performance), and interfacing with the rest of the userspace code. Eventually, the goal is that Qemu should work anywhere, and if a KVM kernel module is available, it could be automatically used. Both teams work actively to keep differences at a minimum, and there are advances in reducing it. Second, KVM is a fork of the Qemu executable. Since it is a new processor mode of execution, the code doesn't have to be modified in any way.Īpart from the processor state switching, the kernel module also handles a few low-level parts of the emulation like the MMU registers (used to handle VM) and some parts of the PCI emulated hardware. The guest state has its own set of ring states, but privileged ring0 instructions fall back to the hypervisor code. KVM is a couple of things: first it is a Linux kernel module-now included in mainline-that switches the processor into a new 'guest' state. This is a lot faster than plain Qemu because most code is unchanged, but still has to transform ring0 code (most of the code in the VM's kernel), so performance still suffers. All the peripheral hardware emulation is done in Qemu. The difference is that instead of recompiling the code, it calls KQemu to scan/patch/execute it. In that case, userspace Qemu still allocates all the RAM for the emulated machine, and loads the code. To make it as efficient as possible on x86 Linux, there's a kernel module called KQemu that handles this.īeing a kernel module, KQemu is able to execute most code unchanged, replacing only the lowest-level ring0-only instructions. In the specific case where both source and target are the same architecture (like the common case of x86 on x86), it still has to parse the code to remove any 'privileged instructions' and replace them with context switches. To emulate more than just the processor, Qemu includes a long list of peripheral emulators: disk, network, VGA, PCI, USB, serial/parallel ports, etc. Mainly it works by a special 'recompiler' that transforms binary code written for a given processor into another one (say, to run MIPS code on a PPC mac, or ARM in an x86 PC).
You use it to emulate machines, it is very flexible and portable. QEmu is a complete and standalone software of its own.
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