Vhost vs virtio

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Vhost vs virtio

The virtio-vhost-user device lets guests act as vhost device backends so that virtual network switches and storage appliance VMs can provide virtio devices to other guests.

In cloud environments everything is a guest. It is not possible for users to run vhost-user processes on the host. This precludes high-performance vhost-user appliances from running in cloud environments. Once the vhost-user session has been established all vring activity can be performed by poll mode drivers in shared memory. This eliminates vmexits in the data path so that the highest possible VM-to-VM communication performance can be achieved.

Even when interrupts are necessary, virtio-vhost-user can use lightweight vmexits thanks to ioeventfd instead of exiting to host userspace. Virtio devices were originally emulated inside the QEMU host userspace process. Later on, vhost allowed a subset of a virtio device, called the vhost device backendto be implement inside the host kernel.

It works by tunneling the vhost-user protocol over a new virtio device type called virtio-vhost-user. VM2 sees a regular virtio-net device. VM2's QEMU uses the existing vhost-user feature as if it were talking to a host userspace vhost-user backend. It is possible to reuse existing vhost-user backend software with virtio-vhost-user since they use the same vhost-user protocol messages.

The driver can be implemented in a guest userspace process using Linux vfio-pci but guest kernel driver implementation would also be also possible. The vhost device backend vrings are accessed through shared memory and do not require vhost-user message exchanges in the data path. No vmexits are taken when poll mode drivers are used.

Even when interrupts are used, QEMU is not involved in the data path because ioeventfd lightweight vmexits are taken. 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 6 Februaryat About QEMU.Jump to navigation.

It was written with network admin users in mind who want to use the vHost-user multiqueue configuration for increased bandwidth to VM vHost-user port types in their Open vSwitch with DPDK server deployment. If using Open vSwitch 2. You can also use the OvS master branchwhich can be downloaded here if you want to have access to the latest development features. Figure 1 shows a standard single queue configuration of vHost-user.

vhost vs virtio

Figure 1: vHost-user default configuration. Hardware: a network interface card NIC configured with one queue Q0 by default; a queue consists of a reception rx and transmission tx path. It also has a single Poll Mode Driver thread PMD 0 by default that is responsible for executing transmit and receive actions on both ports.

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Guest: A VM. This is a problem as a single queue can be a bottleneck; all traffic sent and received from the VM can only pass through this single queue. This provides a method to scale out performance when using vHost-user ports. Figure 2 describes the setup required for two queues to be configured in the VNIC with vHost-user multiqueue. Figure 2: vHost-user multiqueue configuration with two queues.

Figure 3: Test environment.

Under the Hood with Nova, Libvirt, and KVM

This article covers two use cases in which vHost-user multiqueue will be configured and verified within this guide. DPDK The traffic generator is external and connected to the vSwitch via a NIC. There is no specific traffic generator recommended for these tests; traffic generated via software or hardware can be used. However to confirm vHost-user multiqueue functionality, multiple flows are required a minimum of two flows. Below are examples of three flows that can be configured and should cause traffic to be distributed between the multiple queues.

Notice that the destination IP varies. When using a NIC with vHost-multiqueue this is a required property for ingress traffic. All other fields can remain the same for testing purposes.

The NIC is connected to the traffic generator.

5.2. Virtio and vhost_net

Rx queues for the NIC are configured at the vSwitch level. Set the PMD thread configuration to two threads to run on the host. In this example core 2 and core 3 on the host are used. The following sections deal with the specific commands required for each use case.

Launch the VM with the following sample command:.

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Note that the Pre-set maximum for combined channels is 2, but the current hardware settings combined channels is 1. The number of combined channels must be set to 2 in order to use multiqueue.Forums New posts Search forums. What's new New posts Latest activity. Members Current visitors New profile posts Search profile posts. Log in. Search Everywhere Threads This forum This thread. Search titles only. Search Advanced search….

vhost vs virtio

Everywhere Threads This forum This thread. Search Advanced…. New posts. Search forums. JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding. Jan 9, 16 0 1 Hattingen, Germany. Hi all, iam installed Proxmox. Now i would like create a new VM. IDE is "normal" or? Is a driver need at the guest? Windows Server ?? Thanks for help. Aug 29, 14, Container becomes more and more popular for strengths, like low overhead, fast boot-up time, and easy to deploy, etc.

How to use DPDK to accelerate container networking becomes a common question for users. The virtual device, virtio-user, with unmodified vhost-user backend, is designed for high performance user space container networking or inter-process communication IPC. The overview of accelerating container networking by virtio-user is shown in Fig. How is memory shared? So only those virtual memory regions aka, hugepages initialized in DPDK are sent to backend.

It restricts that only addresses in these areas can be used to transmit or receive packets. Data Plane Development Kit Flow Bifurcation How-to Guide 4. Generic flow API - examples 5. PVP reference benchmark setup using testpmd 6. VF daemon VFd 7. Overview 7. Sample Usage 7. Limitations 8. Overview The virtual device, virtio-user, with unmodified vhost-user backend, is designed for high performance user space container networking or inter-process communication IPC.

Sample Usage Here we use Docker as container engine. It also applies to LXC, Rocket with some minor changes. Compile DPDK. Limitations We have below limitations in this solution: Cannot work with —huge-unlink option. As we need to reopen the hugepage file to share with vhost backend. Cannot work with —no-huge option.

Currently, DPDK uses anonymous mapping under this option which cannot be reopened to share with vhost backend. If you have more regions especially when 2MB hugepages are usedthe option, —single-file-segments, can help to reduce the number of shared files. That will bring confusion when sharing hugepage files with backend by name.

Root privilege is a must.Skip to content. Existing virtio net code is used in the guest without modification. There's similarity with vringfd, with some differences and reduced scope - uses eventfd for signalling - structures can be moved around in memory at any time good for migration, bug work-arounds in userspace - write logging is supported good for migration - support memory table and not just an offset needed for kvm common virtio related code has been put in a separate file vhost.

I used Rusty's lguest. What it is not: vhost net is not a bus, and not a generic new system call. No assumptions are made on how guest performs hypercalls.

Userspace hypervisors are supported as well as kvm. How it works: Basically, we connect virtio frontend configured by userspace to a backend. The backend could be a network device, or a tap device. Status: This works for me, and I haven't see any crashes. Compared to userspace, people reported improved latency as I save up to 4 system calls per packetas well as better bandwidth and CPU utilization.

Features that I plan to look at in the future: - mergeable buffers - zero copy - scalability tuning: figure out the best threading model to use Note on RCU usage this is also documented in vhost. Paul's ack below is for this RCU usage. Loading branch information. Unified Split. Showing 14 changed files with 2, additions and 0 deletions.

Oops, something went wrong. You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. M: "Michael S.

49. Poll Mode Driver for Emulated Virtio NIC

L: kvm vger. L: virtualization lists.

vhost vs virtio

L: netdev vger. S: Maintained. If unsure, say N. OK, it's a little counter-intuitive to do this, but it puts it neatly under. This kernel module can be loaded in host kernel to accelerate.

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To compile this driver as a module, choose M here: the module will.This document is intended to provide an overview of how Vhost works behind the scenes. Code snippets used in this document might have been simplified for the sake of readability and should not be used as an API or implementation reference. Reading from the Virtio specification :. Virtio devices use virtqueues to transport data efficiently.

Vhost is a protocol for devices accessible via inter-process communication.

7. Virtio_user for Container Networking

It uses the same virtqueue layout as Virtio to allow Vhost devices to be mapped directly to Virtio devices. See also SPDK optimizations. The initial vhost implementation is a part of the Linux kernel and uses ioctl interface to communicate with userspace applications.

The Vhost-user specification describes the protocol as follows:. SPDK vhost is a Vhost-user slave server. It exposes Unix domain sockets and allows external applications to connect. All initialization and management information is exchanged using Vhost-user messages. The connection always starts with the feature negotiation. Both the Master and the Slave exposes a list of their implemented features and upon negotiation they choose a common set of those.

Most of these features are implementation-related, but also regard e. After the negotiation, the Vhost-user driver shares its memory, so that the vhost device SPDK can access it directly. The memory can be fragmented into multiple physically-discontiguous regions and Vhost-user specification puts a limit on their number - currently 8. The driver sends a single message for each region with the following data:.

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The previous mappings will be removed. Drivers may also request a device config, consisting of e. Afterwards, the driver requests the number of maximum supported queues and starts sending virtqueue data, which consists of:.

If multiqueue feature has been negotiated, the driver has to send a specific ENABLE message for each extra queue it wants to be polled. Other queues are polled as soon as they're initialized. Legacy Virtio implementations used the name vring alongside virtqueue, and the name vring is still used in virtio data structures inside the code.

vhost vs virtio

The device after polling this descriptor chain needs to translate and transform it back into the original request struct. SPDK enforces the request and response data to be contained within a single memory region. There are multiple interrupt coalescing features involved, but they are not be discussed in this document.

Reading from the Virtio specification : The purpose of virtio and [virtio] specification is that virtual environments.Vhost is a kernel acceleration module for virtio qemu backend. With this enhancement, virtio could achieve quite promising performance. In this chapter, we will demonstrate usage of virtio PMD driver with two backends, standard qemu vhost back end and vhost kni back end. In Tx, packets described by the used descriptors in vring are available for virtio to clean.

Virtio will enqueue to be transmitted packets into vring, make them available to the device, and then notify the host back end if necessary. In this release, the virtio PMD driver provides the basic functionality of packet reception and transmission. Other basic DPDK preparations like hugepage enabling, uio port binding are not listed here. This command generates one network device vEth0 for physical port.

If specify more physical ports, the generated network device will be vEth1, vEth2, and so on.

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For each physical port, kni creates two user threads. One thread loops to fetch packets from the physical NIC port into the kni receive queue. The other user thread loops to send packets in the kni transmit queue. Enable the kni raw socket functionality for the specified physical NIC port, get the generated file descriptor and set it in the qemu command line parameter.

In the above example, virtio port 0 in the guest VM will be associated with vEth0, which in turns corresponds to a physical port, which means received packets come from vEth0, and transmitted packets is sent to vEth0. Example of using the vector version of the virtio poll mode driver in testpmd :. There are three kinds of interrupts from a virtio device over PCI bus: config interrupt, Rx interrupts, and Tx interrupts. Config interrupt is used for notification of device configuration changes, especially link status lsc.

Virtio PMD already has support for receiving lsc from qemu when the link status changes, especially when vhost user disconnects.

However, it fails to do that if the VM is created by qemu 2. Enable multi-queue when starting VM, and specify msix vectors in qemu cmdline. A virtio device could also be driven by vDPA vhost data path acceleration driver, and works as a HW vhost backend. This argument is used to specify a virtio device needs to work in vDPA mode.

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Default: 0 disabled. Logically virtio-PMD has 9 paths based on the combination of virtio features Rx mergeable, In-order, Packed virtqueuebelow is an introduction of these features:. If packed virtqueue is not negotiated, below split virtqueue paths will be selected according to below configuration:.

If packed virtqueue is negotiated, below packed virtqueue paths will be selected according to below configuration:. Rx callbacks and Tx callbacks for each virtio path are shown in below table:. If you meet performance drop or some other issues after upgrading the driver or configuration, below steps can help you identify which path you selected and root cause faster.

Data Plane Development Kit Overview of Networking Drivers 2.


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