IPoIB: Connected mode experimental support

The following patch adds experimental support for IPoIB connected
mode, as defined by the draft from the IETF ipoib working group.  The
idea is to increase performance by increasing the MTU from the maximum
of 2K (theoretically 4K) supported by IPoIB on top of UD.  With this
code, I'm able to get 800MByte/sec or more with netperf without
options on a Mellanox 4x back-to-back DDR system.

Some notes on code:
1. SRQ is used for scalability to large cluster sizes
2. Only RC connections are used (UC does not support SRQ now)
3. Retry count is set to 0 since spec draft warns against retries
4. Each connection is used for data transfers in only 1 direction, so
   each connection is either active(TX) or passive (RX).  2 sides that
   want to communicate create 2 connections.
5. Each active (TX) connection has a separate CQ for send completions -
   this keeps the code simple without CQ resize and other tricks
6. To detect stale passive side connections (where the remote side is
   down), we keep an LRU list of passive connections (updated once per
   second per connection) and destroy a connection after it has been
   unused for several seconds. The LRU rule makes it possible to avoid
   scanning connections that have recently been active.

Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 15 insertions, 1 deletions

diff --git a/drivers/infiniband/ulp/ipoib/Kconfig b/drivers/infiniband/ulp/ipoib/Kconfig
index c75322d820d4..af78ccc4ce71 100644
--- a/drivers/infiniband/ulp/ipoib/Kconfig
+++ b/drivers/infiniband/ulp/ipoib/Kconfig
@@ -1,6 +1,6 @@
 config INFINIBAND_IPOIB
         tristate "IP-over-InfiniBand"
-        depends on INFINIBAND && NETDEVICES && INET
+        depends on INFINIBAND && NETDEVICES && INET && (IPV6 || IPV6=n)
         ---help---
           Support for the IP-over-InfiniBand protocol (IPoIB). This
           transports IP packets over InfiniBand so you can use your IB
@@ -8,6 +8,20 @@ config INFINIBAND_IPOIB
 
           See Documentation/infiniband/ipoib.txt for more information
 
+config INFINIBAND_IPOIB_CM
+        bool "IP-over-InfiniBand Connected Mode support"
+        depends on INFINIBAND_IPOIB && EXPERIMENTAL
+        default n
+        ---help---
+          This option enables experimental support for IPoIB connected mode.
+          After enabling this option, you need to switch to connected mode through
+          /sys/class/net/ibXXX/mode to actually create connections, and then increase
+          the interface MTU with e.g. ifconfig ib0 mtu 65520.
+
+          WARNING: Enabling connected mode will trigger some
+          packet drops for multicast and UD mode traffic from this interface,
+          unless you limit mtu for these destinations to 2044.
+
 config INFINIBAND_IPOIB_DEBUG
         bool "IP-over-InfiniBand debugging" if EMBEDDED
         depends on INFINIBAND_IPOIB