a5050c6103
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>
64 lines
2.5 KiB
Plaintext
64 lines
2.5 KiB
Plaintext
Hyper-V network driver
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======================
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Compatibility
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=============
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This driver is compatible with Windows Server 2012 R2, 2016 and
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Windows 10.
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Features
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========
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Checksum offload
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----------------
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The netvsc driver supports checksum offload as long as the
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Hyper-V host version does. Windows Server 2016 and Azure
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support checksum offload for TCP and UDP for both IPv4 and
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IPv6. Windows Server 2012 only supports checksum offload for TCP.
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Receive Side Scaling
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--------------------
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Hyper-V supports receive side scaling. For TCP, packets are
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distributed among available queues based on IP address and port
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number. Current versions of Hyper-V host, only distribute UDP
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packets based on the IP source and destination address.
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The port number is not used as part of the hash value for UDP.
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Fragmented IP packets are not distributed between queues;
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all fragmented packets arrive on the first channel.
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Generic Receive Offload, aka GRO
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--------------------------------
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The driver supports GRO and it is enabled by default. GRO coalesces
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like packets and significantly reduces CPU usage under heavy Rx
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load.
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SR-IOV support
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--------------
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Hyper-V supports SR-IOV as a hardware acceleration option. If SR-IOV
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is enabled in both the vSwitch and the guest configuration, then the
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Virtual Function (VF) device is passed to the guest as a PCI
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device. In this case, both a synthetic (netvsc) and VF device are
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visible in the guest OS and both NIC's have the same MAC address.
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The VF is enslaved by netvsc device. The netvsc driver will transparently
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switch the data path to the VF when it is available and up.
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Network state (addresses, firewall, etc) should be applied only to the
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netvsc device; the slave device should not be accessed directly in
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most cases. The exceptions are if some special queue discipline or
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flow direction is desired, these should be applied directly to the
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VF slave device.
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Receive Buffer
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--------------
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Packets are received into a receive area which is created when device
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is probed. The receive area is broken into MTU sized chunks and each may
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contain one or more packets. The number of receive sections may be changed
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via ethtool Rx ring parameters.
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There is a similar send buffer which is used to aggregate packets for sending.
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The send area is broken into chunks of 6144 bytes, each of section may
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contain one or more packets. The send buffer is an optimization, the driver
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will use slower method to handle very large packets or if the send buffer
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area is exhausted.
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