QEMU is a hosted virtual machine monitor : it emulates the machine's processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it to run a variety of guest operating systems. It also can be used with KVM to run virtual machines at near-native speed by taking advantage of hardware extensions such as Intel VT-x.

QEMU can also do emulation for user-level processes, allowing applications compiled for one architecture to run on another. QEMU has multiple operating modes: [5].

QEMU can save and restore the state of the virtual machine with all programs running. Guest operating systems do not need patching in order to run inside QEMU. The virtual machine can interface with many types of physical host hardware, including the user's hard disks, CD-ROM drives, network cards, audio interfaces, and USB devices. USB devices can be completely emulated, or the host's USB devices can be used, although this requires administrator privileges and does not work with all devices.

Virtual disk images can be stored in a special format qcow or qcow2 that only takes up as much disk space as the guest OS actually uses. The QCOW2 format also allows the creation of overlay images that record the difference from another unmodified base image file.

KVM / QEMU based Windows 10 VM - Step by Step

This provides the possibility for reverting the emulated disk's contents to an earlier state. For example, a base image could hold a fresh install of an operating system that is known to work, and the overlay images are used.

Should the guest system become unusable through virus attack, accidental system destruction, etc. QEMU can emulate network cards of different models which share the host system's connectivity by doing network address translation, effectively allowing the guest to use the same network as the host. QEMU integrates several services to allow the host and guest systems to communicate; for example, an integrated SMB server and network-port redirection to allow incoming connections to the virtual machine.

It can also boot Linux kernels without a bootloader. QEMU does not depend on the presence of graphical output methods on the host system. It can also use an emulated serial line, without any screen, with applicable operating systems.

QEMU does not require administrative rights to run unless additional kernel modules for improving speed like KQEMU are used or certain modes of its network connectivity model are utilized. The whole translation task thus consists of two parts: blocks of target code TBs being rewritten in TCG ops - a kind of machine-independent intermediate notation, and subsequently this notation being compiled for the host's architecture by TCG. Optional optimisation passes are performed between them. TCG requires dedicated code written to support every architecture it runs on.

It also requires that the target instruction translation be rewritten to take advantage of TCG ops, instead of the previously used dyngen ops. This worked by running user mode code and optionally some kernel code directly on the host computer's CPU, and by using processor and peripheral emulation only for kernel-mode and real-mode code.

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KQEMU was initially a closed-source product available free of charge, but starting from version 1. QEMU versions starting with 0. The developers of QVM86 ceased development in January, QEMU supports the following disk image formats: [13].Edit : I turned the cache off completly Set the cache mode to None because I once had an issue with an power outage which resulted in a non functioning windows VM.

You should enable virtualization e. Click on the upper left button to open the New VM window. The first thing you have to do is to select how you would like to install the operating system. In this case we use a Windows 10 ISO image. It shows the hosts ressources as little gray text under the input fields.

We are going to create a custom storage by clicking on Manage. A new window Choose Storage Volume will pop up. The window mainly consists of two parts - Storage pools on the left and the storage volumes on the left side. The first thing to do here is to create a new storage pool. To do so, click on the plus button on the bottom left. Here you can select all kinds of storage pool types. After the storage pool is created, select it on the left side of the window and klick on the plus button above the right table to create a new storage volume.

You should check the minimum requirements for the operating system you are going to install. For best performance choose the raw format. The qcow2 format offers some advanced features such as copy on write and live snapshots Source: proxmox. In addition you need to decide the capacity as well as how much of this capacity should be already allocated at the hosts system.

At the end give the storage a name, this name will be used as a filename. So in my case I would have a win Select Customize configuration before installbecause we need to tweak a few other things, before we start the installation process. If you selected the Customize configuration before install option in the last step, the customization window should have opened automatically.

If not, connect it by clicking connect and set the image location to the according windows We need them while installing windows, thus we need to mount them via a ISO file. This will open the Choose Storage Volume dialog. Optionally you can change the source mode by selecting a given host device.

I usually use the bridged mode, which enables me to assign a own IP address to the VM and make it accessible via the network. Additionally the Cache mode should be set to writeback for best performance None for best stability. With this cache mode you may loose data on power outage.Basically, you can make the most of your hardware to accelerate QEMU virtual machines on Windows: starting with its 2. On Windows, you can achieve a similar speed-up with -accel hax or -enable-haxafter completing a one-time setup process.

If there is also a setting for Execute Disable Bit, make sure that one is enabled as well. In most cases, both settings are enabled by default. After that, if you are on Windows 8 or later, make sure Hyper-V is disabled.

This is especially important for Windows 10, which enables Hyper-V by default. There are a number of ways to disable Hyper-V; one of them is to bring up the Start menu, type Windows Features and Enter, uncheck Hyper-V in the resulting dialog, and click on OK to confirm.

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I recommend getting the latest stable release from here. At the time of this writing, the latest stable release is 2. To boot it, open a new command prompt window, switch to your QEMU installation directory e. VMs like this are hardly usable without hardware acceleration. You may run into issues at some point, because there are, inevitably, bugs in HAXM e. Please create an issue on GitHub if you have a question, bug report or feature request.

Intel CPUs that do not support the said feature are almost extinct now. Windows 7 or later. HAXM works on both bit and bit versions of Windows. If your system is protected against changes to BIOS, e. Note that changing the Hyper-V setting could also trigger the alarm of the tamper protection mechanism e.

BitLocker that may be enabled on your system.

Linux PCI Passthrough VFIO - Performance - Gaming with Windows on Linux

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qemu performance

It only takes a minute to sign up. Intended use is to distribute the VM to customers who might not have "elevated" or "admin" rights on the Windows machine.

The system should be portable, i. Because of this restriction, we ended up with QEMU which does not require special Windows rights to run. You need local Administrator rights to enable it, but once enabled, you can give your users the rights to create and run virtual machines without the need to be full administrators, by placing them in the "Hyper-V Administrators" local group.

The performance are really good, because the virtualization technology is exactly the same used on Hyper-V servers it actually runs under the main OS, although it looks like an application sitting on top of it. VirtualBox might be a better answer to your situation. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered.

Ask Question. Asked 5 years, 7 months ago. Active 1 year, 3 months ago. Viewed 18k times. Additionally, it seems to be end-of-life and 64bit support is experimental. The WinKVM project also seems to be no longer actively developed, and probably also requires admin rights on the Windows host. Martin Heide Martin Heide 61 1 1 gold badge 1 1 silver badge 2 2 bronze badges. That's the only way.

qemu performance

If you really must have Windows, then you virtualize with something else. Unfortunately our customers are mostly Windows users. Do you know a solution that does not require "elevated" or "administrator" rights on the Windows host?

Any specific reason that you cannot have a bootable Linux USB drive? Yes: Our users are mostly Windows users, and they want to work with other software at the same time, e. MS office or CAD programs. Using a bootable USB drive would totally switch context and they would have to find suitable Linux programs for their tasks.

Our customers are not IT experts, so forcing them to use another OS is generally not a good solution.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

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Super User is a question and answer site for computer enthusiasts and power users. It only takes a minute to sign up. I've noticed several articles that have claimed that QEMU is slower than VirtualBox without hardware assistance but several are years old, and the newest seemed to be from last year.

qemu performance

Some of my host systems do not have hardware virtualization support so I'm especially interested in performance tips that work without the kernel module. If you're talking about x86 virtualization on an x86 host, be advised that kqemu the old acceleration kernel module for qemu is deprecated.

The guest can be whatever OS you want as long as it's x86 architecture. It's all emulated in software. So for x86 to x86 virtualization, "raw" qemu is slow, but KVM which uses qemu is fast. Quite fast. But I'd definitely recommend that you check out kvm if you dealing with a server.

Edit: For your hosts that don't have any hardware acceleration, you're going to suffer from a pretty large overhead regardless of which virt solution you use. Emulating hardware things in software is hard, and expensive.

The technical reasons for Qemu being slow with 2D youtube, spreadsheet, games and 3D emulation are obscure to me.

qemu performance

However, I can make a guess that the "video drivers" simply aren't good enough - the graphics hardware in the hardware is not used in an optimal way. Actually it is a few years old and seems reasonably mature.

QEMU Disk IO performance comparison: Native or threads?

The video-performance benefits of running with the QXL video driver are huge in my experience 2D web-development. I don't know how well it compares to Virtualbox, but it's definitely an improvement. This is solely my opinion and It should be noted that I have never even tried to run any 3D or video playback in the guest.

Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Ask Question. Asked 7 years, 9 months ago. Active 3 years, 8 months ago. Viewed 29k times.The TCG works by translating each guest instruction into a sequence of host instructions. As a result there will be a level of inefficiency which means TCG code will not be as fast as running native code. However with a reasonable host system you can get a pretty good experience, especially when emulating older and slower chips.

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Depending on your requirements you can tailor you use of QEMU. If all you want to do is run and debug user space programs then you should use QEMU's user space emulation solution linux-user or bsd-user. Here the guest architecture program is translated to run host instructions up until the point the program makes a system call into the kernel. The system call is then routed to the host kernel to be executed. This is efficient because you don't need to translated a kernel and more importantly you don't need to do a full emulation of the systems address translation subsystem.

You should disable ASLR address space layout randomisation. This is a kernel security feature to make it harder for malicious code to guess memory addresses while trying to execute exploits. However for TCG is means code translations that could otherwise be shared end up being re-translated multiple times. See developer documentation for internal details about how the TCG works. Navigation menu Personal tools Log in.

Namespaces Page Discussion. Views Read View source View history. Get Download License. Learn Documentation Links. This page was last edited on 10 Julyat About QEMU.Modern processors come with a wide variety of performance enhancing features such as streaming instructions sets sse and other performance-enhancing instructions. These features vary from processor to processor. QEMU and KVM default to a compatible subset of cpu features, so that if you change your host processor, or perform a live migration, the guest will see its cpu features unchanged.

This is great for compatibility but comes at a performance cost. If all your hosts have these features, compatibility is retained:. To see the difference between the capabilities of the host CPU versus the guest, just compare the output of the following commands on each system:. For example, the default setting on a 64 bit host machine is "-cpu qemu64". This includes the following flags:.

QEMU defaults to user-mode networking slirpwhich is available without prior setup and without administrative privileges on the host. It is also unfortunately very slow. To get high performance networking, switch to a bridged setup via the -net tap command line switches.

Again this card is compatible with most guests, but does not offer the best performance. If your guest supports it, switch to the virtio model:. QEMU supports a wide variety for storage formats and back-ends. Easiest to use are the raw and qcow2 formats, but for the best performance it is best to use a raw partition. You can create either a logical volume or a partition and assign it to the guest:. QEMU also supports a wide variety of caching modes. If you're using raw volumes or partitions, it is best to avoid the cache completely, which reduces data copies and bus traffic:.

As with networking, QEMU supports several storage interfaces. The default, IDE, is highly supported by guests but may be slow, especially with disk arrays.

If your guest supports it, use the virtio interface:. Don't use the linux filesystem btrfs on the host for the image files. It will result in low IO performance. The kvm guest may even freeze when high IO traffic is done on the guest. Create account Log in. Toggle navigation. Discussion View source History.

Jump to: navigationsearch. CPU Performance Modern processors come with a wide variety of performance enhancing features such as streaming instructions sets sse and other performance-enhancing instructions.

To pass all available host processor features to the guest, use the command line switch qemu -cpu host if you wish to retain compatibility, you can expose selected features to your guest. This includes the following flags: fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx lm up pni hypervisor The host itself might support other flags like cx16, mmxext, and so on.

Networking QEMU defaults to user-mode networking slirpwhich is available without prior setup and without administrative privileges on the host. Storage QEMU supports a wide variety for storage formats and back-ends.


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