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authorstephen hemminger <stephen@networkplumber.org>2017-08-02 05:58:54 +0300
committerDavid S. Miller <davem@davemloft.net>2017-08-03 02:55:33 +0300
commita5050c61036859e6fd7924f25cc6a97e7462039d (patch)
treeb7e14544e35b842e1e1ced836a5c3ad72ef13534 /Documentation/networking
parent0c195567a8f6e82ea5535cd9f1d54a1626dd233e (diff)
downloadlinux-a5050c61036859e6fd7924f25cc6a97e7462039d.tar.xz
netvsc: add documentation
Add some background documentation on netvsc device options and limitations. Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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+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, packets are
+ distributed among available queues based on IP address and port
+ number. Current versions of Hyper-V host, only distribute UDP
+ packets based on the IP source and destination address.
+ The port number is not used as part of the hash value for UDP.
+ Fragmented IP packets are not distributed between queues;
+ all fragmented packets arrive on the first channel.
+
+ 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.