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Documentation / networking / netvsc.txt




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Based on kernel version 4.15. Page generated on 2018-01-29 10:00 EST.

1	Hyper-V network driver
2	======================
3	
4	Compatibility
5	=============
6	
7	This driver is compatible with Windows Server 2012 R2, 2016 and
8	Windows 10.
9	
10	Features
11	========
12	
13	  Checksum offload
14	  ----------------
15	  The netvsc driver supports checksum offload as long as the
16	  Hyper-V host version does. Windows Server 2016 and Azure
17	  support checksum offload for TCP and UDP for both IPv4 and
18	  IPv6. Windows Server 2012 only supports checksum offload for TCP.
19	
20	  Receive Side Scaling
21	  --------------------
22	  Hyper-V supports receive side scaling. For TCP & UDP, packets can
23	  be distributed among available queues based on IP address and port
24	  number.
25	
26	  For TCP & UDP, we can switch hash level between L3 and L4 by ethtool
27	  command. TCP/UDP over IPv4 and v6 can be set differently. The default
28	  hash level is L4. We currently only allow switching TX hash level
29	  from within the guests.
30	
31	  On Azure, fragmented UDP packets have high loss rate with L4
32	  hashing. Using L3 hashing is recommended in this case.
33	
34	  For example, for UDP over IPv4 on eth0:
35	  To include UDP port numbers in hashing:
36	        ethtool -N eth0 rx-flow-hash udp4 sdfn
37	  To exclude UDP port numbers in hashing:
38	        ethtool -N eth0 rx-flow-hash udp4 sd
39	  To show UDP hash level:
40	        ethtool -n eth0 rx-flow-hash udp4
41	
42	  Generic Receive Offload, aka GRO
43	  --------------------------------
44	  The driver supports GRO and it is enabled by default. GRO coalesces
45	  like packets and significantly reduces CPU usage under heavy Rx
46	  load.
47	
48	  SR-IOV support
49	  --------------
50	  Hyper-V supports SR-IOV as a hardware acceleration option. If SR-IOV
51	  is enabled in both the vSwitch and the guest configuration, then the
52	  Virtual Function (VF) device is passed to the guest as a PCI
53	  device. In this case, both a synthetic (netvsc) and VF device are
54	  visible in the guest OS and both NIC's have the same MAC address.
55	
56	  The VF is enslaved by netvsc device.  The netvsc driver will transparently
57	  switch the data path to the VF when it is available and up.
58	  Network state (addresses, firewall, etc) should be applied only to the
59	  netvsc device; the slave device should not be accessed directly in
60	  most cases.  The exceptions are if some special queue discipline or
61	  flow direction is desired, these should be applied directly to the
62	  VF slave device.
63	
64	  Receive Buffer
65	  --------------
66	  Packets are received into a receive area which is created when device
67	  is probed. The receive area is broken into MTU sized chunks and each may
68	  contain one or more packets. The number of receive sections may be changed
69	  via ethtool Rx ring parameters.
70	
71	  There is a similar send buffer which is used to aggregate packets for sending.
72	  The send area is broken into chunks of 6144 bytes, each of section may
73	  contain one or more packets. The send buffer is an optimization, the driver
74	  will use slower method to handle very large packets or if the send buffer
75	  area is exhausted.
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