1 .. SPDX-License-Identifier: BSD-3-Clause
2 Copyright(c) Microsoft Corporation.
4 Netvsc poll mode driver
5 =======================
7 The Netvsc Poll Mode driver (PMD) provides support for the paravirtualized
8 network device for Microsoft Hyper-V. It can be used with
9 Window Server 2008/2012/2016, Windows 10.
10 The device offers multi-queue support (if kernel and host support it),
11 checksum and segmentation offloads.
14 Features and Limitations of Hyper-V PMD
15 ---------------------------------------
17 In this release, the hyper PMD driver provides the basic functionality of packet reception and transmission.
19 * It supports merge-able buffers per packet when receiving packets and scattered buffer per packet
20 when transmitting packets. The packet size supported is from 64 to 65536.
22 * The PMD supports multicast packets and promiscuous mode subject to restrictions on the host.
23 In order to this to work, the guest network configuration on Hyper-V must be configured to allow MAC address
26 * The device has only a single MAC address.
27 Hyper-V driver does not support MAC or VLAN filtering because the Hyper-V host does not support it.
29 * VLAN tags are always stripped and presented in mbuf tci field.
31 * The Hyper-V driver does not use or support interrupts. Link state change
32 callback is done via change events in the packet ring.
34 * The maximum number of queues is limited by the host (currently 64).
35 When used with 4.16 kernel only a single queue is available.
38 This driver is intended for use with **Hyper-V only** and is
39 not recommended for use on Azure because accelerated Networking
40 (SR-IOV) is not supported.
42 On Azure, use the :doc:`vdev_netvsc` which
43 automatically configures the necessary TAP and failsave drivers.
49 The Netvsc PMD is a standalone driver, similar to virtio and vmxnet3.
50 Using Netvsc PMD requires that the associated VMBUS device be bound to the userspace
51 I/O device driver for Hyper-V (uio_hv_generic). By default, all netvsc devices
52 will be bound to the Linux kernel driver; in order to use netvsc PMD the
53 device must first be overridden.
55 The first step is to identify the network device to override.
56 VMBUS uses Universal Unique Identifiers
57 (`UUID`_) to identify devices on the bus similar to how PCI uses Domain:Bus:Function.
58 The UUID associated with a Linux kernel network device can be determined
59 by looking at the sysfs information. To find the UUID for eth1 and
60 store it in a shell variable:
62 .. code-block:: console
64 DEV_UUID=$(basename $(readlink /sys/class/net/eth1/device))
67 .. _`UUID`: https://en.wikipedia.org/wiki/Universally_unique_identifier
69 There are several possible ways to assign the uio device driver for a device.
70 The easiest way (but only on 4.18 or later)
71 is to use the `driverctl Device Driver control utility`_ to override
72 the normal kernel device.
74 .. code-block:: console
76 driverctl -b vmbus set-override $DEV_UUID uio_hv_generic
78 .. _`driverctl Device Driver control utility`: https://gitlab.com/driverctl/driverctl
80 Any settings done with driverctl are by default persistent and will be reapplied
83 On older kernels, the same effect can be had by manual sysfs bind and unbind
86 .. code-block:: console
88 NET_UUID="f8615163-df3e-46c5-913f-f2d2f965ed0e"
89 modprobe uio_hv_generic
90 echo $NET_UUID > /sys/bus/vmbus/drivers/uio_hv_generic/new_id
91 echo $DEV_UUID > /sys/bus/vmbus/drivers/hv_netvsc/unbind
92 echo $DEV_UUID > /sys/bus/vmbus/drivers/uio_hv_generic/bind
96 The dpkd-devbind.py script can not be used since it only handles PCI devices.
102 The following prerequisites apply:
104 * Linux kernel support for UIO on vmbus is done with the uio_hv_generic driver.
105 Full support of multiple queues requires the 4.17 kernel. It is possible
106 to use the netvsc PMD with 4.16 kernel but it is limited to a single queue.
112 The user can specify below argument in devargs.
116 A netvsc device uses a mailbox page to indicate to the host that there
117 is something in the transmit queue. The host scans this page at a
118 periodic interval. This parameter allows adjusting the value that
119 is used by the host. Smaller values improve transmit latency, and larger
120 values save CPU cycles. This parameter is in microseconds.
121 If the value is too large or too small it will be
122 ignored by the host. (Default: 50)