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authorOr Gerlitz <ogerlitz@voltaire.com>2009-04-08 16:52:01 -0400
committerRoland Dreier <rolandd@cisco.com>2009-04-08 16:52:01 -0400
commit6a3335b43342b42dd6c69b4bbbde15d622cb49ca (patch)
treec2ec24376c3f3bac9b76c09373444bcea64a5062 /Documentation/infiniband/ipoib.txt
parentedb5abb1e2a84fd8802a3577d95eac84fe1405ab (diff)
IPoIB: Document newish features
Update the documentation to include connected mode, stateless offloads and interrupt moderation, and add a reference to the connected mode RFC. Signed-off-by: Or Gerlitz <ogerlitz@voltaire.com> Signed-off-by: Roland Dreier <rolandd@cisco.com>
Diffstat (limited to 'Documentation/infiniband/ipoib.txt')
-rw-r--r--Documentation/infiniband/ipoib.txt45
1 files changed, 45 insertions, 0 deletions
diff --git a/Documentation/infiniband/ipoib.txt b/Documentation/infiniband/ipoib.txt
index 864ff3283780..6d40f00b358c 100644
--- a/Documentation/infiniband/ipoib.txt
+++ b/Documentation/infiniband/ipoib.txt
@@ -24,6 +24,49 @@ Partitions and P_Keys
24 The P_Key for any interface is given by the "pkey" file, and the 24 The P_Key for any interface is given by the "pkey" file, and the
25 main interface for a subinterface is in "parent." 25 main interface for a subinterface is in "parent."
26 26
27Datagram vs Connected modes
28
29 The IPoIB driver supports two modes of operation: datagram and
30 connected. The mode is set and read through an interface's
31 /sys/class/net/<intf name>/mode file.
32
33 In datagram mode, the IB UD (Unreliable Datagram) transport is used
34 and so the interface MTU has is equal to the IB L2 MTU minus the
35 IPoIB encapsulation header (4 bytes). For example, in a typical IB
36 fabric with a 2K MTU, the IPoIB MTU will be 2048 - 4 = 2044 bytes.
37
38 In connected mode, the IB RC (Reliable Connected) transport is used.
39 Connected mode is to takes advantage of the connected nature of the
40 IB transport and allows an MTU up to the maximal IP packet size of
41 64K, which reduces the number of IP packets needed for handling
42 large UDP datagrams, TCP segments, etc and increases the performance
43 for large messages.
44
45 In connected mode, the interface's UD QP is still used for multicast
46 and communication with peers that don't support connected mode. In
47 this case, RX emulation of ICMP PMTU packets is used to cause the
48 networking stack to use the smaller UD MTU for these neighbours.
49
50Stateless offloads
51
52 If the IB HW supports IPoIB stateless offloads, IPoIB advertises
53 TCP/IP checksum and/or Large Send (LSO) offloading capability to the
54 network stack.
55
56 Large Receive (LRO) offloading is also implemented and may be turned
57 on/off using ethtool calls. Currently LRO is supported only for
58 checksum offload capable devices.
59
60 Stateless offloads are supported only in datagram mode.
61
62Interrupt moderation
63
64 If the underlying IB device supports CQ event moderation, one can
65 use ethtool to set interrupt mitigation parameters and thus reduce
66 the overhead incurred by handling interrupts. The main code path of
67 IPoIB doesn't use events for TX completion signaling so only RX
68 moderation is supported.
69
27Debugging Information 70Debugging Information
28 71
29 By compiling the IPoIB driver with CONFIG_INFINIBAND_IPOIB_DEBUG set 72 By compiling the IPoIB driver with CONFIG_INFINIBAND_IPOIB_DEBUG set
@@ -55,3 +98,5 @@ References
55 http://ietf.org/rfc/rfc4391.txt 98 http://ietf.org/rfc/rfc4391.txt
56 IP over InfiniBand (IPoIB) Architecture (RFC 4392) 99 IP over InfiniBand (IPoIB) Architecture (RFC 4392)
57 http://ietf.org/rfc/rfc4392.txt 100 http://ietf.org/rfc/rfc4392.txt
101 IP over InfiniBand: Connected Mode (RFC 4755)
102 http://ietf.org/rfc/rfc4755.txt