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Diffstat (limited to 'Documentation/networking/device_drivers/microsoft/netvsc.txt')
| -rw-r--r-- | Documentation/networking/device_drivers/microsoft/netvsc.txt | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/Documentation/networking/device_drivers/microsoft/netvsc.txt b/Documentation/networking/device_drivers/microsoft/netvsc.txt new file mode 100644 index 000000000000..3bfa635bbbd5 --- /dev/null +++ b/Documentation/networking/device_drivers/microsoft/netvsc.txt @@ -0,0 +1,84 @@ +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. + + Large Receive Offload (LRO), or Receive Side Coalescing (RSC) + ------------------------------------------------------------- + The driver supports LRO/RSC in the vSwitch feature. It reduces the per packet + processing overhead by coalescing multiple TCP segments when possible. The + feature is enabled by default on VMs running on Windows Server 2019 and + later. It may be changed by ethtool command: + ethtool -K eth0 lro on + ethtool -K eth0 lro off + + 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. |