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authorJonathan Neuschäfer <j.neuschaefer@gmx.net>2020-03-09 00:14:43 +0300
committerJonathan Corbet <corbet@lwn.net>2020-03-10 20:12:34 +0300
commit19796c348ab62287fc6434f296ae279d7b97e39f (patch)
treec7912efe1f5cfbd0ddc00471b8371cec2bc86e8d /Documentation/mic/scif_overview.rst
parent0150aedda00efe2df9156c57de63f4dea8568e8e (diff)
downloadlinux-19796c348ab62287fc6434f296ae279d7b97e39f.tar.xz
docs: Move Intel Many Integrated Core documentation (mic) under misc-devices
It doesn't need to be a top-level chapter. This patch also updates MAINTAINERS and makes sure the F: lines are properly sorted. Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com> Link: https://lore.kernel.org/r/20200308211519.8414-1-j.neuschaefer@gmx.net Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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-========================================
-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(..)