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authorJonathan Neuschäfer <j.neuschaefer@gmx.net>2020-03-08 22:14:43 +0100
committerJonathan Corbet <corbet@lwn.net>2020-03-10 11:12:34 -0600
commit19796c348ab62287fc6434f296ae279d7b97e39f (patch)
treec7912efe1f5cfbd0ddc00471b8371cec2bc86e8d /Documentation/misc-devices
parent0150aedda00efe2df9156c57de63f4dea8568e8e (diff)
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>
Diffstat (limited to 'Documentation/misc-devices')
-rw-r--r--Documentation/misc-devices/index.rst1
-rw-r--r--Documentation/misc-devices/mic/index.rst16
-rw-r--r--Documentation/misc-devices/mic/mic_overview.rst85
-rw-r--r--Documentation/misc-devices/mic/scif_overview.rst108
4 files changed, 210 insertions, 0 deletions
diff --git a/Documentation/misc-devices/index.rst b/Documentation/misc-devices/index.rst
index f11c5daeada5..c1dcd2628911 100644
--- a/Documentation/misc-devices/index.rst
+++ b/Documentation/misc-devices/index.rst
@@ -20,4 +20,5 @@ fit into other categories.
isl29003
lis3lv02d
max6875
+ mic/index
xilinx_sdfec
diff --git a/Documentation/misc-devices/mic/index.rst b/Documentation/misc-devices/mic/index.rst
new file mode 100644
index 000000000000..3a8d06367ef1
--- /dev/null
+++ b/Documentation/misc-devices/mic/index.rst
@@ -0,0 +1,16 @@
+=============================================
+Intel Many Integrated Core (MIC) architecture
+=============================================
+
+.. toctree::
+ :maxdepth: 1
+
+ mic_overview
+ scif_overview
+
+.. only:: subproject and html
+
+ Indices
+ =======
+
+ * :ref:`genindex`
diff --git a/Documentation/misc-devices/mic/mic_overview.rst b/Documentation/misc-devices/mic/mic_overview.rst
new file mode 100644
index 000000000000..17d956bdaf7c
--- /dev/null
+++ b/Documentation/misc-devices/mic/mic_overview.rst
@@ -0,0 +1,85 @@
+======================================================
+Intel Many Integrated Core (MIC) architecture overview
+======================================================
+
+An Intel MIC X100 device is a PCIe form factor add-in coprocessor
+card based on the Intel Many Integrated Core (MIC) architecture
+that runs a Linux OS. It is a PCIe endpoint in a platform and therefore
+implements the three required standard address spaces i.e. configuration,
+memory and I/O. The host OS loads a device driver as is typical for
+PCIe devices. The card itself runs a bootstrap after reset that
+transfers control to the card OS downloaded from the host driver. The
+host driver supports OSPM suspend and resume operations. It shuts down
+the card during suspend and reboots the card OS during resume.
+The card OS as shipped by Intel is a Linux kernel with modifications
+for the X100 devices.
+
+Since it is a PCIe card, it does not have the ability to host hardware
+devices for networking, storage and console. We provide these devices
+on X100 coprocessors thus enabling a self-bootable equivalent
+environment for applications. A key benefit of our solution is that it
+leverages the standard virtio framework for network, disk and console
+devices, though in our case the virtio framework is used across a PCIe
+bus. A Virtio Over PCIe (VOP) driver allows creating user space
+backends or devices on the host which are used to probe virtio drivers
+for these devices on the MIC card. The existing VRINGH infrastructure
+in the kernel is used to access virtio rings from the host. The card
+VOP driver allows card virtio drivers to communicate with their user
+space backends on the host via a device page. Ring 3 apps on the host
+can add, remove and configure virtio devices. A thin MIC specific
+virtio_config_ops is implemented which is borrowed heavily from
+previous similar implementations in lguest and s390.
+
+MIC PCIe card has a dma controller with 8 channels. These channels are
+shared between the host s/w and the card s/w. 0 to 3 are used by host
+and 4 to 7 by card. As the dma device doesn't show up as PCIe device,
+a virtual bus called mic bus is created and virtual dma devices are
+created on it by the host/card drivers. On host the channels are private
+and used only by the host driver to transfer data for the virtio devices.
+
+The Symmetric Communication Interface (SCIF (pronounced as skiff)) is a
+low level communications API across PCIe currently implemented for MIC.
+More details are available at scif_overview.txt.
+
+The Coprocessor State Management (COSM) driver on the host allows for
+boot, shutdown and reset of Intel MIC devices. It communicates with a COSM
+"client" driver on the MIC cards over SCIF to perform these functions.
+
+Here is a block diagram of the various components described above. The
+virtio backends are situated on the host rather than the card given better
+single threaded performance for the host compared to MIC, the ability of
+the host to initiate DMA's to/from the card using the MIC DMA engine and
+the fact that the virtio block storage backend can only be on the host::
+
+ +----------+ | +----------+
+ | Card OS | | | Host OS |
+ +----------+ | +----------+
+ |
+ +-------+ +--------+ +------+ | +---------+ +--------+ +--------+
+ | Virtio| |Virtio | |Virtio| | |Virtio | |Virtio | |Virtio |
+ | Net | |Console | |Block | | |Net | |Console | |Block |
+ | Driver| |Driver | |Driver| | |backend | |backend | |backend |
+ +---+---+ +---+----+ +--+---+ | +---------+ +----+---+ +--------+
+ | | | | | | |
+ | | | |User | | |
+ | | | |------|------------|--+------|-------
+ +---------+---------+ |Kernel |
+ | | |
+ +---------+ +---+----+ +------+ | +------+ +------+ +--+---+ +-------+
+ |MIC DMA | | VOP | | SCIF | | | SCIF | | COSM | | VOP | |MIC DMA|
+ +---+-----+ +---+----+ +--+---+ | +--+---+ +--+---+ +------+ +----+--+
+ | | | | | | |
+ +---+-----+ +---+----+ +--+---+ | +--+---+ +--+---+ +------+ +----+--+
+ |MIC | | VOP | |SCIF | | |SCIF | | COSM | | VOP | | MIC |
+ |HW Bus | | HW Bus| |HW Bus| | |HW Bus| | Bus | |HW Bus| |HW Bus |
+ +---------+ +--------+ +--+---+ | +--+---+ +------+ +------+ +-------+
+ | | | | | | |
+ | +-----------+--+ | | | +---------------+ |
+ | |Intel MIC | | | | |Intel MIC | |
+ | |Card Driver | | | | |Host Driver | |
+ +---+--------------+------+ | +----+---------------+-----+
+ | | |
+ +-------------------------------------------------------------+
+ | |
+ | PCIe Bus |
+ +-------------------------------------------------------------+
diff --git a/Documentation/misc-devices/mic/scif_overview.rst b/Documentation/misc-devices/mic/scif_overview.rst
new file mode 100644
index 000000000000..4c8ad9e43706
--- /dev/null
+++ b/Documentation/misc-devices/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(..)