Update Linux to v5.4.2
Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/Documentation/mic/scif_overview.rst b/Documentation/mic/scif_overview.rst
new file mode 100644
index 0000000..4c8ad9e
--- /dev/null
+++ b/Documentation/mic/scif_overview.rst
@@ -0,0 +1,108 @@
+========================================
+Symmetric Communication Interface (SCIF)
+========================================
+
+The Symmetric Communication Interface (SCIF (pronounced as skiff)) is a low
+level communications API across PCIe currently implemented for MIC. Currently
+SCIF provides inter-node communication within a single host platform, where a
+node is a MIC Coprocessor or Xeon based host. SCIF abstracts the details of
+communicating over the PCIe bus while providing an API that is symmetric
+across all the nodes in the PCIe network. An important design objective for SCIF
+is to deliver the maximum possible performance given the communication
+abilities of the hardware. SCIF has been used to implement an offload compiler
+runtime and OFED support for MPI implementations for MIC coprocessors.
+
+SCIF API Components
+===================
+
+The SCIF API has the following parts:
+
+1. Connection establishment using a client server model
+2. Byte stream messaging intended for short messages
+3. Node enumeration to determine online nodes
+4. Poll semantics for detection of incoming connections and messages
+5. Memory registration to pin down pages
+6. Remote memory mapping for low latency CPU accesses via mmap
+7. Remote DMA (RDMA) for high bandwidth DMA transfers
+8. Fence APIs for RDMA synchronization
+
+SCIF exposes the notion of a connection which can be used by peer processes on
+nodes in a SCIF PCIe "network" to share memory "windows" and to communicate. A
+process in a SCIF node initiates a SCIF connection to a peer process on a
+different node via a SCIF "endpoint". SCIF endpoints support messaging APIs
+which are similar to connection oriented socket APIs. Connected SCIF endpoints
+can also register local memory which is followed by data transfer using either
+DMA, CPU copies or remote memory mapping via mmap. SCIF supports both user and
+kernel mode clients which are functionally equivalent.
+
+SCIF Performance for MIC
+========================
+
+DMA bandwidth comparison between the TCP (over ethernet over PCIe) stack versus
+SCIF shows the performance advantages of SCIF for HPC applications and
+runtimes::
+
+ Comparison of TCP and SCIF based BW
+
+ Throughput (GB/sec)
+ 8 + PCIe Bandwidth ******
+ + TCP ######
+ 7 + ************************************** SCIF %%%%%%
+ | %%%%%%%%%%%%%%%%%%%
+ 6 + %%%%
+ | %%
+ | %%%
+ 5 + %%
+ | %%
+ 4 + %%
+ | %%
+ 3 + %%
+ | %
+ 2 + %%
+ | %%
+ | %
+ 1 +
+ + ######################################
+ 0 +++---+++--+--+-+--+--+-++-+--+-++-+--+-++-+-
+ 1 10 100 1000 10000 100000
+ Transfer Size (KBytes)
+
+SCIF allows memory sharing via mmap(..) between processes on different PCIe
+nodes and thus provides bare-metal PCIe latency. The round trip SCIF mmap
+latency from the host to an x100 MIC for an 8 byte message is 0.44 usecs.
+
+SCIF has a user space library which is a thin IOCTL wrapper providing a user
+space API similar to the kernel API in scif.h. The SCIF user space library
+is distributed @ https://software.intel.com/en-us/mic-developer
+
+Here is some pseudo code for an example of how two applications on two PCIe
+nodes would typically use the SCIF API::
+
+ Process A (on node A) Process B (on node B)
+
+ /* get online node information */
+ scif_get_node_ids(..) scif_get_node_ids(..)
+ scif_open(..) scif_open(..)
+ scif_bind(..) scif_bind(..)
+ scif_listen(..)
+ scif_accept(..) scif_connect(..)
+ /* SCIF connection established */
+
+ /* Send and receive short messages */
+ scif_send(..)/scif_recv(..) scif_send(..)/scif_recv(..)
+
+ /* Register memory */
+ scif_register(..) scif_register(..)
+
+ /* RDMA */
+ scif_readfrom(..)/scif_writeto(..) scif_readfrom(..)/scif_writeto(..)
+
+ /* Fence DMAs */
+ scif_fence_signal(..) scif_fence_signal(..)
+
+ mmap(..) mmap(..)
+
+ /* Access remote registered memory */
+
+ /* Close the endpoints */
+ scif_close(..) scif_close(..)