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Documentation / infiniband / ipoib.txt




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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:03 EST.

1	IP OVER INFINIBAND
2	
3	  The ib_ipoib driver is an implementation of the IP over InfiniBand
4	  protocol as specified by RFC 4391 and 4392, issued by the IETF ipoib
5	  working group.  It is a "native" implementation in the sense of
6	  setting the interface type to ARPHRD_INFINIBAND and the hardware
7	  address length to 20 (earlier proprietary implementations
8	  masqueraded to the kernel as ethernet interfaces).
9	
10	Partitions and P_Keys
11	
12	  When the IPoIB driver is loaded, it creates one interface for each
13	  port using the P_Key at index 0.  To create an interface with a
14	  different P_Key, write the desired P_Key into the main interface's
15	  /sys/class/net/<intf name>/create_child file.  For example:
16	
17	    echo 0x8001 > /sys/class/net/ib0/create_child
18	
19	  This will create an interface named ib0.8001 with P_Key 0x8001.  To
20	  remove a subinterface, use the "delete_child" file:
21	
22	    echo 0x8001 > /sys/class/net/ib0/delete_child
23	
24	  The P_Key for any interface is given by the "pkey" file, and the
25	  main interface for a subinterface is in "parent."
26	
27	  Child interface create/delete can also be done using IPoIB's
28	  rtnl_link_ops, where childs created using either way behave the same.
29	
30	Datagram vs Connected modes
31	
32	  The IPoIB driver supports two modes of operation: datagram and
33	  connected.  The mode is set and read through an interface's
34	  /sys/class/net/<intf name>/mode file.
35	
36	  In datagram mode, the IB UD (Unreliable Datagram) transport is used
37	  and so the interface MTU has is equal to the IB L2 MTU minus the
38	  IPoIB encapsulation header (4 bytes).  For example, in a typical IB
39	  fabric with a 2K MTU, the IPoIB MTU will be 2048 - 4 = 2044 bytes.
40	
41	  In connected mode, the IB RC (Reliable Connected) transport is used.
42	  Connected mode takes advantage of the connected nature of the IB
43	  transport and allows an MTU up to the maximal IP packet size of 64K,
44	  which reduces the number of IP packets needed for handling large UDP
45	  datagrams, TCP segments, etc and increases the performance for large
46	  messages.
47	
48	  In connected mode, the interface's UD QP is still used for multicast
49	  and communication with peers that don't support connected mode. In
50	  this case, RX emulation of ICMP PMTU packets is used to cause the
51	  networking stack to use the smaller UD MTU for these neighbours.
52	
53	Stateless offloads
54	
55	  If the IB HW supports IPoIB stateless offloads, IPoIB advertises
56	  TCP/IP checksum and/or Large Send (LSO) offloading capability to the
57	  network stack.
58	
59	  Large Receive (LRO) offloading is also implemented and may be turned
60	  on/off using ethtool calls.  Currently LRO is supported only for
61	  checksum offload capable devices.
62	
63	  Stateless offloads are supported only in datagram mode.  
64	
65	Interrupt moderation
66	
67	  If the underlying IB device supports CQ event moderation, one can
68	  use ethtool to set interrupt mitigation parameters and thus reduce
69	  the overhead incurred by handling interrupts.  The main code path of
70	  IPoIB doesn't use events for TX completion signaling so only RX
71	  moderation is supported.
72	
73	Debugging Information
74	
75	  By compiling the IPoIB driver with CONFIG_INFINIBAND_IPOIB_DEBUG set
76	  to 'y', tracing messages are compiled into the driver.  They are
77	  turned on by setting the module parameters debug_level and
78	  mcast_debug_level to 1.  These parameters can be controlled at
79	  runtime through files in /sys/module/ib_ipoib/.
80	
81	  CONFIG_INFINIBAND_IPOIB_DEBUG also enables files in the debugfs
82	  virtual filesystem.  By mounting this filesystem, for example with
83	
84	    mount -t debugfs none /sys/kernel/debug
85	
86	  it is possible to get statistics about multicast groups from the
87	  files /sys/kernel/debug/ipoib/ib0_mcg and so on.
88	
89	  The performance impact of this option is negligible, so it
90	  is safe to enable this option with debug_level set to 0 for normal
91	  operation.
92	
93	  CONFIG_INFINIBAND_IPOIB_DEBUG_DATA enables even more debug output in
94	  the data path when data_debug_level is set to 1.  However, even with
95	  the output disabled, enabling this configuration option will affect
96	  performance, because it adds tests to the fast path.
97	
98	References
99	
100	  Transmission of IP over InfiniBand (IPoIB) (RFC 4391)
101	    http://ietf.org/rfc/rfc4391.txt 
102	  IP over InfiniBand (IPoIB) Architecture (RFC 4392)
103	    http://ietf.org/rfc/rfc4392.txt 
104	  IP over InfiniBand: Connected Mode (RFC 4755)
105	    http://ietf.org/rfc/rfc4755.txt
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