The devices are real hardware devices which are directly assigned to a VM. These are major reasons for better performance than emulated device.
#Lspci on windows drivers
Hypercall has less oeverheads than VM_Exit as we mentioned above.Īnother important thing is, PV drivers are purpose built for virtualization, and they are fully optimized to avoid unnecessary hypercalls. When PV drivers operate the synthetic devices, it uses the hypercall to cooperate with hypervisor. The synthetic devices usually have better performance than emulated devices because virtual drivers in guest can cooperate with hypervisor to avoid lots of overheads than device emulations.
#Lspci on windows driver
The virtual bus driver must provide an OS independent standardrized protocols to probe the devices on the bus. There are no ways to probe the Synthetic Devices without a virtual bus driver in a guest OS. Instead, the devices are created by Hyper-V,Īnd only can be driven by PV drivers in guest OS. The devices are not emulated devices, and there are no such kind of hardware devices in real world. When physical drivers access the emulated device registers, it will result a VM_Exit to call into the hypervisor device emulation code.īecause VM_Exit overhead is bigger than a hypercall, and unmodified physical drivers never avoid such overheads, the emulated devices performance never can be better than other two device types. The emulated devices usually have worst performance than other two types of devices, as the hardware emulation introduce lots of performance overheads in data path. It will be detected by lspci command in Linux guest OS. For example, If a hardware is emulated as a PCI device, The emulated devices could be probed or detected by low level tools and firmware which are based on well known hardware/bus standards. That means drivers in guest OS just drive the hardware devices as same as they do for physical devices.Ī legacy OS without any Hyper-V knowledge wouldn’t work if emulated devices were not supported. The devices are emulated by Hyper-V and acting as the real hardware. Hyper-V actually supports 3 type of devices in a guest VM, In order to get better IO performance, it supports a set of PV(Para Virtualization) Drivers to optimize the data path.
#Lspci on windows full
For major kernel part, it leverages Hardware-assisted Virtualization which is still called Full Virtualization.Today, the major performance overheads in Full Virtualization VMs are caused by IO bound workloads.įor this reason, most of guest OS uses a Hybrid way to get better performance, The Full Virtualization VM could perform better than Para Virtualization VM while running the CPU or memory bound workload. However, after Intel/AMD introduced the Hardware-assisted Virtualization extensions, such as The mechanism that allows guest OS to cooperate with hypervisor is called by a special terminology: hypercall.Īt early phases, Para Virtualization usually provides the better performance than Full Virtualization on x86 platform. When a VM is working under this mode, the OS must have the virtualization knowledge, which means the OS is modified for cooperating with underlying hypervisors.
With this virtualization type, application running over legacy OS like old Linux, Windows, and DOS could be easily migrated to a VM. If a VM is working under this mode, OS without any virtualization knowledge can run over VM very well, just like running over the bare-metal hardware. Today, most of hypervisors provide two virtualization types, In order to have better understandings of the specification, there are some key concepts need to be clarified.
#Lspci on windows windows
For Hyper-V,Įmulated and synthetic hardware specification for Windows Server 2012 Hyper-V is a such kind of specification. The contents here are limited to Hyper-V, but some basic virtualization concepts might be similar or same with other hypervisors.Įvery hypervisor actually defines a clear specification for a virtual hardware inventory provisioned for a guest VM. This article tries to give an overview about the virtual platform provided by Hyper-V, and how Linux OS works in a guest VM.
Similar with other virtualization technologies， Hyper-V creates a virtual platform for its virtual machine. The content reuse need include the original link: Home list tags talk user link rss Hyper-V Virtual Devices
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