Patent Application
20230096894
Embodiments of the present disclosure relate to multi-core neural networks, and more specifically, to flexible and energy-efficient 2-D router mesh.
According to embodiments of the present disclosure, a flexible and energy efficient router mesh is provided. An array of neural cores is provided. The array has at least two dimensions. Each of the neural cores comprises a plurality of ordered input wires, a plurality of ordered output wires, and a plurality of synapses, each of the synapses operatively coupled to one of the plurality of input wires and one of the plurality of output wires. A plurality of signal wires is provided. At least one of the plurality of signal wires is disposed along each dimension of the array of neural cores. Each of the plurality of signal wires is disposed along at least one dimension of the array. A plurality of routers is provided, each of which is operatively coupled to (i) one of the plurality of neural cores and (ii) at least two of the signal wires, one along each of the dimensions of the array of neural cores. Each of the plurality of routers is configured to selectively route a signal from one of its at least two coupled signal wires to its coupled neural core. Each of the plurality of routers is configured to selectively route a signal from its coupled neural core to one of its at least two coupled signal wires.
According to embodiments of the present disclosure, methods of operating an array of neural network cores is provided. Signals are received at a plurality of routers via a plurality of signal wires. Each of the plurality of routers selectively routes the signals from at least one signal wire to a neural core. The router selectively routes a signal from the neural core to the plurality of signal wires. The neural core comprises a plurality of ordered input wires, a plurality of ordered output wires, and a plurality of synapses, each of the synapses operatively coupled to one of the plurality of input wires and one of the plurality of output wires. At least one of the plurality of signal wires is disposed along each dimension of an array of neural cores comprising the neural core, the array having at least two dimensions. Each of the plurality of signal wires is disposed along at least one dimension of the array. Each of the plurality of routers is configured to selectively route a signal from one of its at least two coupled signal wires to its coupled neural core. Each of the plurality of routers is configured to selectively route a signal from its coupled neural core to one of its at least two coupled signal wires.
Artificial neural networks (ANNs) are distributed computing systems, which consist of a number of neurons interconnected through connection points called synapses. Each synapse encodes the strength of the connection between the output of one neuron and the input of another. The output of each neuron is determined by the aggregate input received from other neurons that are connected to it. Thus, the output of a given neuron is based on the outputs of connected neurons from the preceding layer and the strength of the connections as determined by the synaptic weights. An ANN is trained to solve a specific problem (e.g., pattern recognition) by adjusting the weights of the synapses such that a particular class of inputs produce a desired output.
ANNs may be implemented on various kinds of hardware, including crossbar arrays, also known as crosspoint arrays or crosswire arrays. A basic crossbar array configuration includes a set of conductive row wires and a set of conductive column wires formed to intersect the set of conductive row wires. The intersections between the two sets of wires are separated by crosspoint devices. Crosspoint devices function as the ANN's weighted connections between neurons.
In various embodiments, a nonvolatile memory-based crossbar array, or crossbar memory, is provided. A plurality of junctions are formed by row lines intersecting column lines. A resistive memory element, such as a non-volatile memory, is in series with a selector at each of the junctions coupling between one of the row lines and one of the column lines. The selector may be a volatile switch or a transistor, various types of which are known in the art. It will be appreciated that a variety of resistive memory elements are suitable for use as described herein, including memristors, phase-change memories, conductive-bridging RAMs, spin-transfer torque RAMs.
A fixed number of synapses may be provided on a core, and then multiple cores connected to provide a complete neural network. In such embodiments, interconnectivity between cores is provided to convey outputs of the neurons on one core to another core, for example, via a packet-switched or circuit-switched network. In a packet-switched network, greater flexibility of interconnection may be achieved, at a power and speed cost due to the need to transmit, read, and act on address bits. In a circuit-switched network, no address bits are required, and so flexibility and re-configurability must be achieved through other means.
In various exemplary networks, a plurality of cores is arranged in an array on a chip. In such embodiments, relative positions of cores may be referred to by the cardinal directions (north, south, east, west).
In the context of physical arrays of neural cores comprising analog memory elements, the present disclosure provides for flexible routing of signals between array cores of for the purpose of neuromorphic computation. In various embodiments, the data carried by these neural signals are encoded in the pulse-duration carried by each wire, using digital voltage levels suitable for buffering or other forms of digital signal restoration. In other embodiments, data can be directly time-multiplexed as binary pulses representing digital place-value bits, coordinated with edges on local or forwarded clock-signals used for latching the said digital place-value bits at the destination.
While a multiply-accumulate operation can be efficiently performed in a single step within such core arrays, there remains the problem of conveying that output data from the output peripheral circuitry at the edge of one core to the input peripheral circuitry at the edge of some other core. To implement flexible and reconfigurable hardware, the ability to support arbitrary routing paths from any one core to any other core(s) is desirable. While deep learning applications do not require the full flexibility offered by packet-switched networks, it is desirable to support both single-casting and multi-casting of the data from the output neurons of one core to the associated input neurons of multiple other array cores.
In various embodiments of the present disclosure, each neuron on the edge of each core is connectable to a dedicated routing fabric for that particular neuron. The routing fabric comprises a mesh of wires, buffers, and switches that are associated with that particular neuron within the overall data vector corresponding to all neurons at the core edge. While the routing fabric for a single neuron is described in various examples herein, it will be understood that all neurons (or elements of the data-vector) travel in parallel on their own dedicated routing lines. In various embodiments, one or more control lines control all or a substantial fraction of the parallel lines simultaneously. In other embodiments, a register of mask bits allows masked control of a subset of the parallel lines.
As described above, in some embodiments, routers on north, east, south and west edges of a tile are connected to the plus-sign-shaped wiring—two long wires stretching across the array, one horizontal and one vertical, connected by one or more vias at their crossing point. Thus, even when it is only necessary to send signals directly from south edge to north edge (or west and east), additional energy is incurred due to the larger capacitance of the plus-sign wiring.
To address this, in alternative embodiments, borderguard circuitry is provided that is capable of buffering and complex signal routing, together with three wire meshes. The meshes include one plus-sign mesh, one horizontal-only mesh, and one vertical-only mesh. The advantage of this approach is that overall energy usage is reduced when it is only necessary to send data vectors directly across tiles and compute cores. Other combinations of plus-sign and direct-linear meshes could be created by extending this methodology.
The borderguard circuit described here combines an A and B port on one side and an A′ and B′ port on the other. Incoming data from two mesh ports (e.g., A and B) can be buffered and send to the other pair of ports (A′ and B′). In keeping with the upstream/downstream concept described throughout, the same circuit is capable of treating A′ and B′ as the inputs, and A and B as the outputs. This provides the ability to choose to swap the exit roles (B input goes to A′ output, while A input goes to B′ output). This opens up the opportunity to steer data from one mesh to another when passing through each borderguard.
In various embodiments, there are the three wire meshes that sit above each tile or compute-core: one plus-sign mesh, one horizontal-only mesh, and one vertical-only mesh. The two latter meshes can be constructed by starting with two parallel plus-sign meshes, and then removing the connecting vias for one of the two meshes. Since every row and column has its own borderguard circuit and its own set of mesh wires, this creates a full parallel 2D data-mesh.
A borderguard sitting on the West edge of a tile can receive data on two horizontal input wires (coming from further West), buffer it and pass it on Eastward on two horizontal wires sitting over its tile. Since one of those horizontal wires is connected only to the East side of the tile, energy can be saved by using this wire when the data-transport scheme does not require transport of these data vectors to the north or south ports of the tile. Yet data can still be arbitrarily routed across the 2-D mesh to any destination, using the plus-sign mesh when multi-casting to more than one destination and/or switching from a horizontal path to a vertical path (or vice-versa).
Referring now to
It will be appreciated that during operation as a classifier, the array of cores may be trained using a variety of methods known in the art. Certain algorithms may be suitable for specific tasks such as image recognition, speech recognition, or language processing. Training algorithms lead to a pattern of synaptic weights that, during the learning process, converges toward an optimal solution of the given problem. Backpropagation is one suitable algorithm for supervised learning, in which a known correct output is available during the learning process. The goal of such learning is to obtain a system that generalizes to data that were not available during training.
In general, during backpropagation, the output of the network is compared to the known correct output. An error value is calculated for each of the neurons in the output layer. The error values are propagated backwards, starting from the output layer, to determine an error value associated with each neuron. The error values correspond to each neuron's contribution to the network output. The error values are then used to update the weights. By incremental correction in this way, the network output is adjusted to conform to the training data. During backpropagation, the vectors of data may be travelling between cores in the opposite direction to that used during forward propagation. Accordingly, if data-vectors were passed from the south side of, e.g., core 3 to the west-side of, e.g., core 4 during forward-propagation, during back-propagation, data-vectors may need to be passed in reverse: from the west side of core 4 to the south side of core 3.
When applying backpropagation, an ANN rapidly attains high accuracy on most of the examples in a training-set. The vast majority of training time is spent trying to further increase this test accuracy. During this time, a large number of the training data examples lead to little correction, since the system has already learned to recognize those examples. While in general, ANN performance tends to improve with the size of the data set, this can be explained by the fact that larger data-sets contain more borderline examples between the different classes on which the ANN is being trained.
Accordingly, during training, array 100 may be provided with example data and example labels. Inferred classifications may be provided as output. Based on the inferred classifications, weight overrides may be provided to the array of cores. In turn, updated weights may be read from the array.
With reference now to
Lines 201 . . . 204 provide connectivity between cores in the array and correspond to lines 102 in
Transmission gates 209, 210 (labelled ROW_connect and COLUMN_connect) are provided at the entrance to the ROW 211 and COLUMN 212 neuron circuitry of each core. Each neuron circuit can thereby be connected to (or isolated from) an associated router wire through a transmission gate. In some embodiments, transmission gates are implemented as PFET and NFET connected source to source and drain to drain, with complementary drive signals. In exemplary embodiments, the entrance to columns correspond to the south side of the core and the entrance to rows correspond to the west side of the core.
Transmission gates 213 . . . 216 surround buffer 217. By correctly configuring transmission gates 205 . . . 208 between the cores (labelled WEST, EAST, SOUTH, NORTH); transmission gates 209, 210 at the entrance to each neuron circuit (labelled ROW_connect and COLUMN_connect); and transmission gates 213 . . . 216 surrounding the buffers (labelled DOWN_in, UP_in, DOWN_out, and UP_out), this router can be used to provide circuit-switched routing for each neuron from a neuron circuit on any edge of one array-core, to neuron circuits on the edge of any other array-cores.
In a multi-core environment, the router wire (e.g., 201 . . . 204, which are individual elements of lines 102) passes in the vicinity of each neuron circuitry (e.g., 211, 212, which are individual elements of array 111), and connects via transmission gates (e.g., 205 . . . 208) to the router wire in the next core (to the north, south, east, or west) and to buffer circuitry (e.g., 217) located at each core.
In various embodiments, for simplicity, the router wiring for NORTH and WEST are hard-wired to each other, and the router wiring for SOUTH and EAST are hard-wired to each other. In such embodiments, the buffer circuitry can be used to boost the signal either downstream (NORTH/WEST to SOUTH/EAST) or upstream (vice versa).
Referring to
As pictured, in some embodiments, buffer circuitry can be organized so that its location is coordinated to either the row position of the associated neuron circuitry or the column position, and not both.
Accordingly, durations or binary data generated in the periphery (encoding data) are placed, by borderguard circuitry onto wiring that runs across the core array. These signals can be buffered or blocked at other borderguard circuits until they arrive at the target core.
In various embodiments, the buffer circuitry and its transmission gates are placed within the array at periodic positions within the array, at positions that are correlated with the column position and independent of the row (or vice-versa, as needed). The transmission gates between arrays sit at the exterior edges of neuron circuitry, while the transmission gates at the entrance of the neuron circuitry can be included at the appropriate part of the neuron circuitry. As shown in
Referring to
The gates in this example are configured for multicast routing. The output of a COLUMN neuron on the SOUTH side of core 401 is routed to the ROW neurons on the WEST side of cores that are both close and distant neighbors to this core. Transmission gates that will be CLOSED to enforce this routing network are shown in light gray—open transmission gates remain in their original color. Note that signals are buffered as they pass over any array core in the UPSTREAM/DOWNSTREAM direction, but signals that are passed by the hard-coded connections (e.g., from NORTH to WEST or vice-versa, or from SOUTH to EAST or vice-versa) do not get buffered. Closed transmission gates are shown in grey.
Here the column neurons on the south side of core 401 are driving the router fabric. Open transmission gates within core 404 allow transmission and buffering of this vector of signals as they pass over core 404 but are ignored by row and column neurons of core 404. However, the open transmission gates between cores 404 and 405, between 405 and 402, and between 402 and 403 allow the vector of signals to arrive at the row neurons on the west edge of core 403. Simultaneously, the vector of signals is buffered by the buffers situated within core 405 and the open transmission gates at the borderguard circuit (described further below) between cores 405 and 406, allowing the same vector of signals to arrive at the row neurons on the west edge of core 406. As a result, the data-vector has been multicast from the south side of core 401 to the west sides of both cores 403 and 406, with two buffering stages along the way.
Referring to
In this example, the borderguard circuitry contains the necessary transmission gates and buffers. Accordingly, additional circuitry is not placed within the core itself. While such an embodiment requires slightly larger area because of the need for four inverters instead of two, it provides advantages in terms of buffering at every edge. In addition, this configuration allows row or column neurons at the edge of a core to receive input through the CONNECT_TO_OUT switch from the router fabric over a neighboring core, while a different signal is simultaneously passing over that array core. In such a condition, by closing the transmission gates INSIDE and CONNECT_TO_IN, the row or column neuron can receive data from either the inside-the-array-core portion of the router mesh, or from the outside-the-array-core portion of the router mesh, or neither, without disrupting the transmission of neuron data either downstream (using the PASS_IN transmission gate) or upstream (through the PASS_OUT transmission gate).
Core 501 includes shared circuitry 502 that performs the function of a borderguard, allowing signals in and out of the corresponding edge of the core. At pitch, higher-level wiring 503 is provided to interconnect the cores (corresponding, e.g., to leads 102). The borderguard shared circuitry allows signals in and out of the west and south edges of core 501.
Referring to
Referring to
It will be appreciated that the routing pictured in
Referring to
This routing exemplified in
Referring now to
Encoder register bits en<0:4,9> provide logical control over these input and output options, as well as over the enablement of tri-state buffers for driving the large-capacitance wires (en<5:8>).
Note that care must be taken to avoid control options that are nonsensible, such as actively driving the same wire being used for input, or by enabling two input paths which could potentially lead to logical OR operations between the duration signals or digital data signals encoded onto those wires.
Referring to Table 1, control masks are provided for the circuit of
In this exemplary circuit, it will be appreciated that the following routings are not supported. However, it will be appreciated that alternative embodiments enable such routing.
NW<0>->NW<1>
NW<1>->NW<0>
SE<0>->SE<1>
SE<1>->SE<0>
DB_out->DB_in
In an exemplary reference implementation utilizing a 14 nm FinFet technology node, a layout with 28 gates has a total width of 8.832 μm and a height of 1.26 μm.
Referring to
Referring to
Referring to
Inward vertical express lanes 1113 . . . 1116 extend between the northern borderguards and the southern borderguards Inward horizontal express lanes 1117 . . . 1120 extend between the western and eastern borderguards. Inward local crosspoint lanes likewise extend between opposed borderguards and define crosspoints 1121 . . . 1124.
In this embodiment, the data receiving points 1125 . . . 1128 (local_out and local_in) are located in the borderguard circuits 1129. Accordingly, in such embodiments, data is transferred between the edge borderguards and internally placed circuits.
Referring to
Referring to
Referring to
Referring now to
In computing node 10 there is a computer system/server 12, which is operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well-known computing systems, environments, and/or configurations that may be suitable for use with computer system/server 12 include, but are not limited to, personal computer systems, server computer systems, thin clients, thick clients, handheld or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputer systems, mainframe computer systems, and distributed cloud computing environments that include any of the above systems or devices, and the like.
Computer system/server 12 may be described in the general context of computer system-executable instructions, such as program modules, being executed by a computer system. Generally, program modules may include routines, programs, objects, components, logic, data structures, and so on that perform particular tasks or implement particular abstract data types. Computer system/server 12 may be practiced in distributed cloud computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed cloud computing environment, program modules may be located in both local and remote computer system storage media including memory storage devices.
As shown in
Bus 18 represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, Peripheral Component Interconnect (PCI) bus, Peripheral Component Interconnect Express (PCIe), and Advanced Microcontroller Bus Architecture (AMBA).
Computer system/server 12 typically includes a variety of computer system readable media. Such media may be any available media that is accessible by computer system/server 12, and it includes both volatile and non-volatile media, removable and non-removable media.
System memory 28 can include computer system readable media in the form of volatile memory, such as random access memory (RAM) 30 and/or cache memory 32. Computer system/server 12 may further include other removable/non-removable, volatile/non-volatile computer system storage media. By way of example only, storage system 34 can be provided for reading from and writing to a non-removable, non-volatile magnetic media (not shown and typically called a “hard drive”). Although not shown, a magnetic disk drive for reading from and writing to a removable, non-volatile magnetic disk (e.g., a “floppy disk”), and an optical disk drive for reading from or writing to a removable, non-volatile optical disk such as a CD-ROM, DVD-ROM or other optical media can be provided. In such instances, each can be connected to bus 18 by one or more data media interfaces. As will be further depicted and described below, memory 28 may include at least one program product having a set (e.g., at least one) of program modules that are configured to carry out the functions of embodiments of the disclosure.
Program/utility 40, having a set (at least one) of program modules 42, may be stored in memory 28 by way of example, and not limitation, as well as an operating system, one or more application programs, other program modules, and program data. Each of the operating system, one or more application programs, other program modules, and program data or some combination thereof, may include an implementation of a networking environment. Program modules 42 generally carry out the functions and/or methodologies of embodiments as described herein.
Computer system/server 12 may also communicate with one or more external devices 14 such as a keyboard, a pointing device, a display 24, etc.; one or more devices that enable a user to interact with computer system/server 12; and/or any devices (e.g., network card, modem, etc.) that enable computer system/server 12 to communicate with one or more other computing devices. Such communication can occur via Input/Output (I/O) interfaces 22. Still yet, computer system/server 12 can communicate with one or more networks such as a local area network (LAN), a general wide area network (WAN), and/or a public network (e.g., the Internet) via network adapter 20. As depicted, network adapter 20 communicates with the other components of computer system/server 12 via bus 18. It should be understood that although not shown, other hardware and/or software components could be used in conjunction with computer system/server 12. Examples, include, but are not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data archival storage systems, etc.
The present disclosure may be embodied as a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present disclosure.
The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.
Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device.
Computer readable program instructions for carrying out operations of the present disclosure may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present disclosure.
Aspects of the present disclosure are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.
These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks.
The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks.
The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.
The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
