Patent Publication Number: US-2023155919-A1

Title: Quality metrics for optimization tasks in generation of a network

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of and claims benefit to U.S. Non-provisional application Ser. No. 17/129,950 filed on Dec. 22, 2020 by Moez CHERIF et al. and titled SYSTEM AND METHOD FOR GENERATION OF QUALITY METRICS FOR OPTIMIZATION TASKS IN TOPOLOGY SYNTHESIS OF A NETWORK, the entire disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The invention is in the field of network design and, more specifically, related to generating and using quality metrics in topology synthesis of a network-on-chip (NoC). 
     BACKGROUND 
     Multiprocessor systems have been implemented in systems-on-chips (SoCs) that communicate through network-on-chips (NoCs). The SoCs include instances of master (initiators) intellectual properties (IPs) and slave (targets) IPs. Transactions, in the form of packets, are sent from a master to one or more slaves using industry-standard protocols. The master, connected to the NoC, sends a request transaction to a slave, using an address to select the slave. The NoC decodes the address and transports the request from the master to the slave. The slave handles the transaction and sends a response transaction, which is transported back by the NoC to the master. 
     For a given set of performance requirements, such as connectivity and latency between source and destination, frequency of the various elements, maximum area available for the NoC logic, minimum throughput between sources and destinations, position on the floorplan of elements attached to the NoC, it is a complex task to create an optimal NoC that fulfills all the requirements with a minimum amount of logic and wires. This is typically the job of the chip architect or chip designer to create this optimal NoC, and this is a difficult and time-consuming task. In addition to this being a difficult task, the design of the NoC is revised every time one of the requirement changes, such as modifications of the chip floorplan or modification of the expected performance. As a result, this task needs to be redone frequently over the design time of the chip. This process is time consuming, which results in production delays. 
     As indicated, it is a complex task to create an optimal NoC that fulfills all the requirements in term of performance and a minimized the amount of logic and wires used. This is a difficult and time-consuming task. Also, the design of the NoC is revised every time one of the requirements changes. As a result, optimization of the NoC is redone frequently over the design time. Various processes are contemplated to automatically create a NoC, when given a set of constraints. Regardless of the process used to create automatically a NoC, the results produced by the automated process need to be assessed to determine the quality of the result or output. Therefore, what is needed is a system and method to analyze a NoC and produces quality metrics for a given generated solution for the NoC. 
     SUMMARY 
     In accordance with various embodiments and aspects of the invention, systems and methods are disclosed that analyze a network-on-chip (NoC) and produce quality metrics for a given generated solution for the NoC. The system and method disclosed include a process that implements optimization strategies to maximize the quality of the result, which allows the designer to understand if the result produced is a good, an average or a bad solution. The advantage of the invention includes simplification of the design process and the work of the designer by using quality metrics generated for the network. Various quality metrics are determined. These quality metrics provide an approach for quality evaluation. The quality metrics can determine the quality of the optimization of a generated network. The quality metrics include analyzing paths and edges in the network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to understand the invention more fully, reference is made to the accompanying drawings. The invention is described in accordance with the aspects and embodiments in the following description with reference to the drawings or figures (FIG.), in which like numbers represent the same or similar elements. Understanding that these drawings are not to be considered limitations in the scope of the invention, the presently described aspects and embodiments and the presently understood best mode of the invention are described with additional detail through use of the accompanying drawings. 
         FIG.  1 A  shows a logic view of a network-on-chip (NoC) that includes various elements that create the NoC. 
         FIG.  1 B  shows a NoC including elements placed on a floorplan of a network. 
         FIG.  2    shows a process for determining actual vs optimal distances between a source (R) and sink (S) pair of endpoints in accordance with the aspects and embodiments of the invention. 
         FIG.  3 A  shows a block diagram of a floorplan with a fly path and the shortest path in accordance with the aspects and embodiments of the invention. 
         FIG.  3 B  shows a block diagram of a floorplan with an actual path and a fly path in accordance with the aspects and embodiments of the invention. 
         FIG.  4    shows a process for clustering or merging edges in a NoC in accordance with the various aspects and embodiments of the invention. 
         FIG.  5 A  shows a block diagram pre-clustering of edges in a NoC in accordance with various aspects and embodiments of the invention. 
         FIG.  5 B  shows a block diagram of clustered edges in a NoC in accordance with various aspects and embodiments of the invention. 
         FIG.  6    shows a floorplan including connection mapping in accordance with the various aspects and embodiments of the invention. 
         FIG.  7    shows the floorplan of  FIG.  6    including logical edges and switches in accordance with the various aspects and embodiments of the invention. 
         FIG.  8    shows the floorplan of  FIG.  7    including segment paths in accordance with the various aspects and embodiments of the invention. 
         FIG.  9    shows the floorplan of  FIG.  8    including an optimal path and an actual path in accordance with the various aspects and embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes various examples of the present technology that illustrate various aspects and embodiments of the invention. Generally, examples can use the described aspects in any combination. All statements herein reciting principles, aspects, and embodiments as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of the structure. 
     It is noted that, as used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Reference throughout this specification to “one aspect,” “an aspect,” “certain aspects,” “various aspects,” or similar language means that a particular aspect, feature, structure, or characteristic described in connection with any embodiment is included in at least one embodiment of the invention. 
     Appearances of the phrases “in one embodiment,” “in at least one embodiment,” “in an embodiment,” “in certain embodiments,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment or similar embodiments. Furthermore, aspects and embodiments of the invention described herein are merely exemplary, and should not be construed as limiting of the scope or spirit of the invention as appreciated by those of ordinary skill in the art. The disclosed invention is effectively made or used in any embodiment that includes any novel aspect described herein. All statements herein reciting principles, aspects, and embodiments of the invention are intended to encompass both structural and functional equivalents thereof. It is intended that such equivalents include both currently known equivalents and equivalents developed in the future. 
     As used herein, a “source, a “master,” and an “initiator” refer to intellectual property (IP) blocks, units, or modules. The terms “source,” “master,” and “initiator” are used interchangeably within the scope and embodiments of the invention. As used herein, a “sink,” a “destination,” a “slave,” and a “target” refer to IP blocks; the terms are used interchangeably within the scope and embodiments of the invention. As used herein, a “transaction” is either a request transaction or a response transaction. Examples of request transactions include write request and read request. 
     Transactions travel from source to destination using a route or communication path that passes through a Network-on-Chip (NoC), which includes various links and switches (a type of node). The terms “path” and “route” are used interchangeable herein. Paths includes and are made up of any combination of nodes and edges (also referred to herein as links), along which data travels form source to destination. In accordance with the various aspects and embodiments of the invention, performing edge clustering minimizes long edges. Many long edges traversing a narrow corridor between 2 or more forbidden regions (blocked areas), which leads to wire congestion. Minimizing the wiring of long edges contributes to lowering congestion. In accordance with the various aspects and embodiments of the invention, the length of an edge (link) is measured as the length of the routed wires between the edge&#39;s end points. 
     As used herein, a node is defined as a distribution point or a communication endpoint that is capable of creating, receiving, and/or transmitting information over a communication path or channel. A node may refer to any one of the following: switches, splitters, mergers, buffers, and adapters. As used herein, splitters and mergers are switches; not all switches are splitters or mergers. As used herein and in accordance with the various aspects and embodiments of the invention, the term “splitter” describes a switch that has a single ingress port and multiple egress ports. As used herein and in accordance with the various aspects and embodiments of the invention, the term “merger” describes a switch that has a single egress port and multiple ingress ports. 
     Referring now to  FIG.  1 A , a network-on-chip (NoC)  100  is shown in accordance with various aspects and embodiments of the invention. NoCs are a special type of network (or interconnect) that are used to handle communication between units of a system on chip (SoC). As discussed below, switches route flows of traffic between sources and destinations and perform arbitration. Adapters deal with various conversions between data width, clock, and power domains. Buffers are used to insert pipelining elements to span long distances, or to store packets to deal with rate adaptation between fast senders and slow receivers or vice-versa. The number and precise functions of each network elements depend on the network on chip technology employed. The NoC elements are implemented on a chip as logic functions using digital logic. 
     The NoC  100  is one example of a network. In accordance with various aspects and embodiments of the invention, a network includes a set of nodes and set of edges, each of these has a model and can be used at the heart of the topology synthesis process to perform and implement transformation over the network and converge to the best solution fitting the specified requirements. The NoC  100  includes nodes and endpoints and uses elementary network functions that are assembled, such as: network interface units (NIUs)  102 , 104 , 106 , 108 ,  110 ,  112 ,  130 ,  132 , and  134 ; nodes/switches  114 ,  116 ,  118 , 120 , and  122 ; buffers, such as buffer  124 ; and adapters, such as adapter  126 . The NoC&#39;s elementary functions (which are represented by components that implement the functions) use an internal NoC transport protocol to communicate with each other, based on the transmission of packets. NIUs convert the protocol used by the attached SoC unit (IP bloc), into the transport protocol used inside the NoC. The NoC elementary network functions use an internal transport protocol, which is specific to the NoC  100 , to communicate with each other, typically based on the transmission of packets. The NIUs convert the protocol used by the attached system-on-chip (SoC) unit (not shown), into the transport protocol used inside the NoC  100 . The switches route flows of traffic between source and destinations. The buffer  124  is used to insert pipelining elements to span long distances, or to store packets to deal with rate adaptation between fast senders and slow receivers or vice-versa. The adapter  126  handles various conversions between data width, clock and power domains. 
     Referring now to  FIG.  1 B , a NoC  150  is shown with various elements, such as NIUs, switches, and blockage areas in the floorplan. The NoC  150  includes various connectivity elements through various switches. In accordance with one aspect of the invention, a set of constraints are used as input to the tool, which is discussed in greater detail below. In accordance with some aspects of the invention, the tool executes a set of sub-steps and produces the description (topology synthesis) of a resulting NoC, such as the NoC  150 , with its configured elements and the position of each element on the floorplan. The generated description is used to actually implement the NoC hardware, using the physical information produced to provide guidance to the back-end implementation flow 
     Referring now to  FIG.  2   , disclosed is a process for determining one NoC quality metric (quantitative network quality metric) in accordance with the various aspects and embodiments of the invention. At step  210 , a network description and constraints for the network, such as a NoC, is loaded in memory. The description of the NoC can be loaded from any source, such as a disk or transmitted from a remote location. The format encoding the data can be any format and the scope of the invention is not limited thereby. At step  212 , the process selects one source and sink pair (R, S). At step  214 , the route information between (R, S) is retrieved for analysis. The route information includes the sequence of switches through which the route travels. At step  216 , the shorted path (or wire length) for an optimal path is determine or computed. The length of the shortest path for the pair (R, S) is identified as LO. At step  218 , the actual path or wire length for the pair (R, S) is computed when traveling from the source to the destination or sink through the NoC. This is determined by adding all the successive paths along the route between successive nodes that the route traverses. The total actual wire length or path length is determined and is identified as L 1 . This is discussed in greater detail with respect to  FIG.  3 A  and  FIG.  3 B . 
     Thus, for each source (connected to the example network, a NoC) in communication with a destination, a minimum distance (shortest path) is computed. In accordance with one aspect of the invention, the minimum distance algorithm, which determines the distance from the source to the destination, considers blocked areas of the floorplan that cannot have logic and wires. The minimum distance algorithm can use of any of the well-known routing algorithms such as Djikstra, A*, etc. and the scope of the invention is not limited thereby. Once a minimum distance is determined, this is used as a reference. 
     In accordance with some aspects and embodiments of the invention, L 0  and L 1  are stored in memory. At step  220 , the difference between the actual path (L 1 ) and the ideal path (L 0 ) is determined to produce the deviation for the route of the pair (R, S). The deviation is stored in memory and mapped for the pair (R, S). At step  230 , the process determined if all possible pairs (R, S) have been processed. If not, the at step  232 , another pair (R 1 , S 1 ) is selected and the process returns to step  214 . This repeated until all pairs (R n , S n ) have been processed. State another way, the path length taken (through the NoC) to go from the source to the destination is calculated. Also, the minimum distance for the same pair of (source, destination) points is calculated. The length of the actual path taken and the length of the minimum distance are compared to determine a difference for the pair of (source, destination) points. This difference represents the difference path measurement. This is performed for all the pairs (source, destination) and a set of differences is produced. Once all pairs have been processed, as determined at step  230 , then at step  240  the process uses all the stored difference for all the pairs (R n , S n ) to generate a histogram presentation of the computed differences and to compute an average difference value. 
     In accordance with one aspect of the invention, this set of differences is used to generate a report using an average difference. In addition and in accordance with various aspects and embodiments of the invention, this set of differences can be reported as a list of differences shown as a sorted list or as a histogram. The result of the differences is also used to generate an average of the differences. This produces one type of quality metric. 
     The quality metric is a representation of an average of the differences between theoretical minimum distance on the floorplan and actual distances taken by the signal traveling from source to destination through the NoC or the network. The quality metric is an indication of how good (or how bad) the latencies will be through the NoC. The latency through the NoC measures how long it takes for a message to traverse or cross the NoC from source to destination. Latency is impacting the performance of components attached to the NoC, such as a CPU. Therefore, the smaller the difference between the actual and minimum distance, the better the performance of the NoC; state another way, the lower the latency. 
     Referring now to  FIG.  3 A  and  FIG.  3 B , in accordance with one example of an aspect and embodiment of the invention, a network&#39;s floorplan  300  is shown with blocked areas  310 , a source or initiator  320  (R) that communicates with a destination or target  330  (S) through a route that traverses switches  322  in the network or NoC. The route is represented by a fly path  340  (broken line). The fly path  340  is a visual representation of the connection between the initiator  320  and the target  300 . The fly path  340  is represented by a minimum distance path  350 . The minimum distance path  350  is compared to an actual path  352 , and is determined by a minimum distance finding algorithm (A* in this non-limiting example). In accordance with some aspects and embodiments of the invention, the algorithm is a combination of such minimum distance algorithm and other heuristics, such as the ones used to create a roadmap. 
     In accordance with one aspect and embodiment of the invention, the actual path  352  includes four segments of length l 0 , l 1 , l 2 , and l 3  that are connected via switches  322 . The actual total paths length is L 1 , which is determined as follows: 
     
       
      
       L 
       1 
       =l 
       0 
       +l 
       1 
       +l 
       2 
       ,+l 
       3  
      
     
     The segments of length l 0 , l 1 , l 2 , and l 3  are Manhattan paths, which are routed using vertical and horizontal segments. The difference between the length L 1  (of the actual path  352 ) and the minimum distance path L 0  (the minimum or optimal path  350 ) is the difference between the aggregated length of the segments of the actual paths and the aggregated lengths of the optimal network paths. The process uses these path length calculation in the process of  FIG.  2   . 
     Referring now to  FIG.  4   , a process is show in accordance with the various aspects and embodiments of the invention for determining another NoC quality metric or quantitative network quality metric. At step  410 , segments, also called edges, of the NoC or network are stored in memory with the NoC constraints. The format encoding the NoC description does not limit the scope of the invention. As indicated herein, at step  410  the sets of segments (for a pair of source, sink (R, S)) are stored in memory. The sets of stored segments are examined for clustering of the links or edges. 
     In accordance with one aspect and embodiment of the invention, at step  420  merging of edges (segments) or clustering of edges is performed. Edge clustering aims to minimize resources and enhancing performance goals through proper algorithms and techniques. In accordance with some aspects of the invention, edge clustering is applied in conjunction and in cooperation with node clustering. Edge clustering and node clustering can be used in combination by mixing, by being applied concurrently, or by being applied in sequence. The advantage and goal is to expand the spectrum of topology synthesis and span a larger solution space for the network. 
     The process of clustering uses proximity and direction of the flow of transported packets: when two segments (edges) are close enough in proximity, and are carrying packets in the same direction, one is removed and only the other is kept. If two segments S1 and S2 are close, in the same direction, and of very different length, the longest segment (e.g. S2) is split into two or three sub-segments (e.g. S2.1, S2.2, S2.3), so that one of the sub-segments (e.g. S2.2) is of the same length as the other segment (e.g. S1) to which the merge is to be attempted. Then clustering is attempted. The clustering is based on an assimilation scheme (merging) between sets of edges that are either horizontal or vertical, and transport packets in the same direction, for instance left to right, right to left, up to down or down to up. 
     In accordance with one embodiment and aspect of the invention, the clustering algorithm considers other requirements, such as performances or avoidance of deadlocks, to decide when to assimilate two segments and cluster the segments. The clustering algorithm attempts to pair as many segments as possible. The clustering mechanism continues until no more segments are left close to another. 
     At step  430 , the difference between actual path length and merged path length is computed. The aggregated length of the set of segments, which is left after clustering, represent a “minimum” network in term of used wires; thus, it gives an idea of the amount of wires the NoC is using compared to a theoretical minimum. More wires result in more logic gates and more area needed. Hence, the closer to the minimum network used wires is to the theoretical minimum, the better the NoC is. 
     At step  440 , the average difference (between actual network aggregated length and theoretical minimum network aggregated length) is computed and presented, in accordance with one aspect and embodiment of the invention. The information is used to generate a report based on an average difference. In addition and in accordance with various aspects and embodiments of the invention, this set of differences can be reported as a list of differences shown as a sorted list, or as a histogram. The result is an average of the differences that represents the quality metric based on wire length derived from merged edges. 
     Referring now to  FIG.  5 A  and  FIG.  5 B , a block diagram of a floorplan  500  is shown for implementing the process of determining the quality metric in accordance with the various aspects and embodiments of the invention. The floorplan  500  includes blocked areas  510 . Two sources  520  are in communication with two targets  530  using edges  550  and  540 . The process merges edges  540  to produce edge  542 . The process merges edges  550  to produce edge  552 . 
     Referring now to  FIG.  6    through  FIG.  9   , the process for merging or collapsing edges is shown in various stages and in accordance with the various aspects and embodiments of the invention. Initiators are in communication with multiple targets, as shown. The fly paths are shown in broken lines and not labelled for clarity. Looking specifically at an example of a route or communication path between one initiator (INIT 1 ) and one target (TARG 3 ), the connection map is shown in  FIG.  6    using just fly paths or routes.  FIG.  7    shows the logical edges (shown as fly paths with broken lines) of the network along with switches connecting the edges. As shown, INIT 1  communicates with TARG 3  using a direct fly path as one option. Also shown, INIT 1  communicates with TARG 3  using the logical route that traverses three segments connected by two switches. Any number of paths and switch are considered for connecting INIT 1  and TARG 3 , all of which are within the scope of the various aspects and embodiments of the invention.  FIG.  8    shows the detailed segments that represent the possible edges connecting INIT 1  and TARG 3 .  FIG.  9    shows optimal path P 13  connecting INIT 1  and TARG 3 . P 13  represents the wirelength of the optimal collision-free path that directly connects INIT 1  and TARG 3 . In addition to the optimal collision-free path, there is a route p 1 -p 2 -p 3  from INIT 1  to TARG 3  that travels through switches sw 1  and sw 2 . The route is the actual route through the NoC. The sum of the wirelength for the route p 1 -p 2 -p 3  is the sum of the wirelengths of all the collision-free paths along the route from INIT 1  to sw 1  to sw 2  to TARG 3 . The routes implement the connectivity. In accordance with the aspects of the invention, a route is an ordered list of network elements, one for each pair of (initiator, target) and one for each pair of (target, initiator). The route represents how traffic between the pairs will flow and through which elements. 
     Thus, the total wirelength from INIT 1  to TARG 3  is represent as follows: 
         WL (INIT1, TARG3)= WL ( p 1)+ WL ( p 2)+ WL ( p 3) 
     The total optimal WL from INIT 1  to TARG 3  is represented as follows: 
       Optimal  WL=WL ( P 13) 
     In accordance with the various aspects and embodiments of the invention, the same process is applied to all the pairs of initiator-target that are represented by a connection in the connection map to determine the quality metric. 
     Certain methods according to the various aspects of the invention may be performed by instructions that are stored upon a non-transitory computer readable medium. The non-transitory computer readable medium stores code including instructions that, if executed by one or more processors, would cause a system or computer to perform steps of the method described herein. The non-transitory computer readable medium includes: a rotating magnetic disk, a rotating optical disk, a flash random access memory (RAM) chip, and other mechanically moving or solid-state storage media. Any type of computer-readable medium is appropriate for storing code comprising instructions according to various example. 
     Certain examples have been described herein and it will be noted that different combinations of different components from different examples may be possible. Salient features are presented to better explain examples; however, it is clear that certain features may be added, modified and/or omitted without modifying the functional aspects of these examples as described. 
     Various examples are methods that use the behavior of either or a combination of machines. Method examples are complete wherever in the world most constituent steps occur. For example and in accordance with the various aspects and embodiments of the invention, IP elements or units include: processors (e.g., CPUs or GPUs), random-access memory (RAM—e.g., off-chip dynamic RAM or DRAM), a network interface for wired or wireless connections such as ethernet, WiFi, 3G, 4G long-term evolution (LTE), 5G, and other wireless interface standard radios. The IP may also include various I/O interface devices, as needed for different peripheral devices such as touch screen sensors, geolocation receivers, microphones, speakers, Bluetooth peripherals, and USB devices, such as keyboards and mice, among others. By executing instructions stored in RAM devices processors perform steps of methods as described herein. 
     Some examples are one or more non-transitory computer readable media arranged to store such instructions for methods described herein. Whatever machine holds non-transitory computer readable media comprising any of the necessary code may implement an example. Some examples may be implemented as: physical devices such as semiconductor chips; hardware description language representations of the logical or functional behavior of such devices; and one or more non-transitory computer readable media arranged to store such hardware description language representations. Descriptions herein reciting principles, aspects, and embodiments encompass both structural and functional equivalents thereof. Elements described herein as coupled have an effectual relationship realizable by a direct connection or indirectly with one or more other intervening elements. 
     Practitioners skilled in the art will recognize many modifications and variations. The modifications and variations include any relevant combination of the disclosed features. Descriptions herein reciting principles, aspects, and embodiments encompass both structural and functional equivalents thereof. Elements described herein as “coupled” or “communicatively coupled” have an effectual relationship realizable by a direct connection or indirect connection, which uses one or more other intervening elements. Embodiments described herein as “communicating” or “in communication with” another device, module, or elements include any form of communication or link and include an effectual relationship. For example, a communication link may be established using a wired connection, wireless protocols, near-filed protocols, or RFID. 
     To the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a similar manner to the term “comprising.” 
     The scope of the invention, therefore, is not intended to be limited to the exemplary embodiments shown and described herein. Rather, the scope and spirit of present invention is embodied by the appended claims.