76 lines
2.9 KiB
Plaintext
76 lines
2.9 KiB
Plaintext
|
Hyper-V network driver
|
||
|
|
======================
|
||
|
|
|
||
|
|
Compatibility
|
||
|
|
=============
|
||
|
|
|
||
|
|
This driver is compatible with Windows Server 2012 R2, 2016 and
|
||
|
|
Windows 10.
|
||
|
|
|
||
|
|
Features
|
||
|
|
========
|
||
|
|
|
||
|
|
Checksum offload
|
||
|
|
----------------
|
||
|
|
The netvsc driver supports checksum offload as long as the
|
||
|
|
Hyper-V host version does. Windows Server 2016 and Azure
|
||
|
|
support checksum offload for TCP and UDP for both IPv4 and
|
||
|
|
IPv6. Windows Server 2012 only supports checksum offload for TCP.
|
||
|
|
|
||
|
|
Receive Side Scaling
|
||
|
|
--------------------
|
||
|
|
Hyper-V supports receive side scaling. For TCP & UDP, packets can
|
||
|
|
be distributed among available queues based on IP address and port
|
||
|
|
number.
|
||
|
|
|
||
|
|
For TCP & UDP, we can switch hash level between L3 and L4 by ethtool
|
||
|
|
command. TCP/UDP over IPv4 and v6 can be set differently. The default
|
||
|
|
hash level is L4. We currently only allow switching TX hash level
|
||
|
|
from within the guests.
|
||
|
|
|
||
|
|
On Azure, fragmented UDP packets have high loss rate with L4
|
||
|
|
hashing. Using L3 hashing is recommended in this case.
|
||
|
|
|
||
|
|
For example, for UDP over IPv4 on eth0:
|
||
|
|
To include UDP port numbers in hashing:
|
||
|
|
ethtool -N eth0 rx-flow-hash udp4 sdfn
|
||
|
|
To exclude UDP port numbers in hashing:
|
||
|
|
ethtool -N eth0 rx-flow-hash udp4 sd
|
||
|
|
To show UDP hash level:
|
||
|
|
ethtool -n eth0 rx-flow-hash udp4
|
||
|
|
|
||
|
|
Generic Receive Offload, aka GRO
|
||
|
|
--------------------------------
|
||
|
|
The driver supports GRO and it is enabled by default. GRO coalesces
|
||
|
|
like packets and significantly reduces CPU usage under heavy Rx
|
||
|
|
load.
|
||
|
|
|
||
|
|
SR-IOV support
|
||
|
|
--------------
|
||
|
|
Hyper-V supports SR-IOV as a hardware acceleration option. If SR-IOV
|
||
|
|
is enabled in both the vSwitch and the guest configuration, then the
|
||
|
|
Virtual Function (VF) device is passed to the guest as a PCI
|
||
|
|
device. In this case, both a synthetic (netvsc) and VF device are
|
||
|
|
visible in the guest OS and both NIC's have the same MAC address.
|
||
|
|
|
||
|
|
The VF is enslaved by netvsc device. The netvsc driver will transparently
|
||
|
|
switch the data path to the VF when it is available and up.
|
||
|
|
Network state (addresses, firewall, etc) should be applied only to the
|
||
|
|
netvsc device; the slave device should not be accessed directly in
|
||
|
|
most cases. The exceptions are if some special queue discipline or
|
||
|
|
flow direction is desired, these should be applied directly to the
|
||
|
|
VF slave device.
|
||
|
|
|
||
|
|
Receive Buffer
|
||
|
|
--------------
|
||
|
|
Packets are received into a receive area which is created when device
|
||
|
|
is probed. The receive area is broken into MTU sized chunks and each may
|
||
|
|
contain one or more packets. The number of receive sections may be changed
|
||
|
|
via ethtool Rx ring parameters.
|
||
|
|
|
||
|
|
There is a similar send buffer which is used to aggregate packets for sending.
|
||
|
|
The send area is broken into chunks of 6144 bytes, each of section may
|
||
|
|
contain one or more packets. The send buffer is an optimization, the driver
|
||
|
|
will use slower method to handle very large packets or if the send buffer
|
||
|
|
area is exhausted.
|