About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / mic / mic_overview.txt




Custom Search

Based on kernel version 4.8. Page generated on 2016-10-06 23:18 EST.

1	An Intel MIC X100 device is a PCIe form factor add-in coprocessor
2	card based on the Intel Many Integrated Core (MIC) architecture
3	that runs a Linux OS. It is a PCIe endpoint in a platform and therefore
4	implements the three required standard address spaces i.e. configuration,
5	memory and I/O. The host OS loads a device driver as is typical for
6	PCIe devices. The card itself runs a bootstrap after reset that
7	transfers control to the card OS downloaded from the host driver. The
8	host driver supports OSPM suspend and resume operations. It shuts down
9	the card during suspend and reboots the card OS during resume.
10	The card OS as shipped by Intel is a Linux kernel with modifications
11	for the X100 devices.
12	
13	Since it is a PCIe card, it does not have the ability to host hardware
14	devices for networking, storage and console. We provide these devices
15	on X100 coprocessors thus enabling a self-bootable equivalent
16	environment for applications. A key benefit of our solution is that it
17	leverages the standard virtio framework for network, disk and console
18	devices, though in our case the virtio framework is used across a PCIe
19	bus. A Virtio Over PCIe (VOP) driver allows creating user space
20	backends or devices on the host which are used to probe virtio drivers
21	for these devices on the MIC card. The existing VRINGH infrastructure
22	in the kernel is used to access virtio rings from the host. The card
23	VOP driver allows card virtio drivers to communicate with their user
24	space backends on the host via a device page. Ring 3 apps on the host
25	can add, remove and configure virtio devices. A thin MIC specific
26	virtio_config_ops is implemented which is borrowed heavily from
27	previous similar implementations in lguest and s390.
28	
29	MIC PCIe card has a dma controller with 8 channels. These channels are
30	shared between the host s/w and the card s/w. 0 to 3 are used by host
31	and 4 to 7 by card. As the dma device doesn't show up as PCIe device,
32	a virtual bus called mic bus is created and virtual dma devices are
33	created on it by the host/card drivers. On host the channels are private
34	and used only by the host driver to transfer data for the virtio devices.
35	
36	The Symmetric Communication Interface (SCIF (pronounced as skiff)) is a
37	low level communications API across PCIe currently implemented for MIC.
38	More details are available at scif_overview.txt.
39	
40	The Coprocessor State Management (COSM) driver on the host allows for
41	boot, shutdown and reset of Intel MIC devices. It communicates with a COSM
42	"client" driver on the MIC cards over SCIF to perform these functions.
43	
44	Here is a block diagram of the various components described above. The
45	virtio backends are situated on the host rather than the card given better
46	single threaded performance for the host compared to MIC, the ability of
47	the host to initiate DMA's to/from the card using the MIC DMA engine and
48	the fact that the virtio block storage backend can only be on the host.
49	
50	               +----------+           |             +----------+
51	               | Card OS  |           |             | Host OS  |
52	               +----------+           |             +----------+
53	                                      |
54	        +-------+ +--------+ +------+ | +---------+  +--------+ +--------+
55	        | Virtio| |Virtio  | |Virtio| | |Virtio   |  |Virtio  | |Virtio  |
56	        | Net   | |Console | |Block | | |Net      |  |Console | |Block   |
57	        | Driver| |Driver  | |Driver| | |backend  |  |backend | |backend |
58	        +---+---+ +---+----+ +--+---+ | +---------+  +----+---+ +--------+
59	            |         |         |     |      |            |         |
60	            |         |         |     |User  |            |         |
61	            |         |         |     |------|------------|--+------|-------
62	            +---------+---------+     |Kernel                |
63	                      |               |                      |
64	  +---------+     +---+----+ +------+ | +------+ +------+ +--+---+  +-------+
65	  |MIC DMA  |     |  VOP   | | SCIF | | | SCIF | | COSM | | VOP  |  |MIC DMA|
66	  +---+-----+     +---+----+ +--+---+ | +--+---+ +--+---+ +------+  +----+--+
67	      |               |         |     |    |        |                    |
68	  +---+-----+     +---+----+ +--+---+ | +--+---+ +--+---+ +------+  +----+--+
69	  |MIC      |     |  VOP   | |SCIF  | | |SCIF  | | COSM | | VOP  |  | MIC   |
70	  |HW Bus   |     |  HW Bus| |HW Bus| | |HW Bus| | Bus  | |HW Bus|  |HW Bus |
71	  +---------+     +--------+ +--+---+ | +--+---+ +------+ +------+  +-------+
72	      |               |         |     |       |     |                    |
73	      |   +-----------+--+      |     |       |    +---------------+     |
74	      |   |Intel MIC     |      |     |       |    |Intel MIC      |     |
75	      |   |Card Driver   |      |     |       |    |Host Driver    |     |
76	      +---+--------------+------+     |       +----+---------------+-----+
77	                 |                    |                   |
78	             +-------------------------------------------------------------+
79	             |                                                             |
80	             |                    PCIe Bus                                 |
81	             +-------------------------------------------------------------+
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.