Update the documentation to include connected mode, stateless offloads and interrupt moderation.
Signed-off-by: Or Gerlitz <[email protected]> Index: linus-linux-2.6/Documentation/infiniband/ipoib.txt =================================================================== --- linus-linux-2.6.orig/Documentation/infiniband/ipoib.txt +++ linus-linux-2.6/Documentation/infiniband/ipoib.txt @@ -24,6 +24,46 @@ Partitions and P_Keys The P_Key for any interface is given by the "pkey" file, and the main interface for a subinterface is in "parent." +Datagram vs Connected modes + + The driver supports two modes of operation - datagram and connected. + The mode is set/read through the /sys/class/net/ibXXX/mode device entry. + + For datagram mode, the IB UD (Unrelaible Datagram) transport is used + and as such the device MTU has very close proximity to the IB L2 MTU + which is typically 2k (larger MTU of 4K supported by the code). + + For connected mode, the IB RC (Reliable Connection) transport is used. + The main reasoning behind connected mode is to take advantage of the + connected nature of the IB transport and use MTUs up to the maximal + IP packet size of 64K - which reduces the number of IP packets needed for + handling large UDP datagrams, TCP segments, etc and increases the performance. + + Under connected mode, the device UD QP is still used for multicast and + communication with peers who don't support connected mode. In this case, + RX emulation of ICMP PMTU packets is used for having the stack use + the smaller UD MTU for these neighbours. + +Stateless offloads + + In case the underlying IB HW supports that, IPoIB advertizes TCP checksum + and/or Large Send (LSO) offloading capability to the network stack. This + is done by the device setting the relevant bits on its features bitmask. + + Large Receive (LRO) offloading is also implemented and may be turned on/off + using ethtool calls, for the time being its supported only for checksum + offload capable devices. + + Offloads are supported only under datagram mode. + +Interrupt moderation + + In case the underlying IB device supports CQ event moderation, one can + have run time control on the rate of interrupt being generated and thus + reduce the overhead incurred by handling interrupts. For the most case + IPoIB doesn't use events for TX completion signaling and as such, only + RX moderation is supported. + Debugging Information By compiling the IPoIB driver with CONFIG_INFINIBAND_IPOIB_DEBUG set @@ -55,3 +95,5 @@ References http://ietf.org/rfc/rfc4391.txt IP over InfiniBand (IPoIB) Architecture (RFC 4392) http://ietf.org/rfc/rfc4392.txt + IP over InfiniBand: Connected Mode (RFC 4755) + http://ietf.org/rfc/rfc4755.txt _______________________________________________ general mailing list [email protected] http://lists.openfabrics.org/cgi-bin/mailman/listinfo/general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
