Update README with information about uGNI and vader BTLs. Also remove references to the csum pml.

cmr=v1.7.3:reviewer=jsquyres

This commit was SVN r28911.

README

@@ -484,10 +484,10 @@ Collectives
 Network Support
 ---------------
 
-- There are three MPI network models available: "ob1", "csum", and
-  "cm".  "ob1" and "csum" use BTL ("Byte Transfer Layer") components
-  for each supported network.  "cm" uses MTL ("Matching Tranport
-  Layer") components for each supported network.
+- There are three MPI network models available: "ob1", and "cm". "ob1"
+  uses BTL ("Byte Transfer Layer") components for each supported network.
+  "cm" uses MTL ("Matching Tranport Layer") components for each supported
+  network.
 
   - "ob1" supports a variety of networks that can be used in
     combination with each other (per OS constraints; e.g., there are
@@ -503,12 +503,8 @@ Network Support
     - SCTP
     - uDAPL
     - Cisco usNIC
-
-  - "csum" is exactly the same as "ob1", except that it performs
-    additional data integrity checks to ensure that the received data
-    is intact (vs. trusting the underlying network to deliver the data
-    correctly).  csum supports all the same networks as ob1, but there
-    is a performance penalty for the additional integrity checks.
+    - uGNI (Cray Gemini, Ares)
+    - vader (xpmem)
 
   - "cm" supports a smaller number of networks (and they cannot be
     used together), but may provide better better overall MPI
@@ -521,14 +517,12 @@ Network Support
 
     Open MPI will, by default, choose to use "cm" when the InfiniPath
     PSM or the Mellanox MXM MTL can be used.  Otherwise, "ob1" will be
-    used and the corresponding BTLs will be selected.  "csum" will never
-    be selected by default.  Users can force the use of ob1 or cm if
-    desired by setting the "pml" MCA parameter at run-time:
+    used and the corresponding BTLs will be selected. Users can force
+    the use of ob1 or cm if desired by setting the "pml" MCA parameter
+    at run-time:
 
       shell$ mpirun --mca pml ob1 ...
       or
-      shell$ mpirun --mca pml csum ...
-      or
       shell$ mpirun --mca pml cm ...
 
 - MXM is a MellanoX Messaging library utilizing full range of IB
@@ -546,6 +540,9 @@ Network Support
   Although the usNIC is accessed via the OpenFabrics / Verbs API
   stack, this BTL is specific to the Cisco usNIC device.
 
+- uGNI is a Cray library for communicating over the Gemini and Ares
+  interconnects.
+
 - The OpenFabrics Enterprise Distribution (OFED) software package v1.0
   will not work properly with Open MPI v1.2 (and later) due to how its
   Mellanox InfiniBand plugin driver is created.  The problem is fixed
@@ -598,7 +595,7 @@ Network Support
   resulting in lower performances in case of non-contiguous
   data-types.
 
-  The "ob1" and "csum" PMLs and BTL components use Open MPI's internal
+  The "ob1" PML and BTL components use Open MPI's internal
   on-node shared memory and process loopback devices for high
   performance.  The BTL interface allows multiple devices to be used
   simultaneously.  For the MX BTL it is recommended that the first
@@ -624,6 +621,11 @@ Network Support
 
   See http://runtime.bordeaux.inria.fr/knem/ for details on Knem.
 
+- XPMEM is used by the vader shared-memory BTL when the XPMEM
+  libraries are installed. XPMEM allows Open MPI to map pages from
+  other processes into the current process' memory space. This
+  allows single-copy semantics for shared memory without the need
+  for a system call.
 
 Open MPI Extensions
 -------------------