Communication abstraction is the main interface between the programming model and the system implementation. With the advancement of hardware capacity, the demand for a well-performing application also increased, which in turn placed a demand on the development of the computer architecture. 28. In wormhole routing, the transmission from the source node to the destination node is done through a sequence of routers. and engineering applications (like reservoir modeling, airflow analysis, combustion efficiency, etc.). A receive operation does not in itself motivate data to be communicated, but rather copies data from an incoming buffer into the application address space. Despite the fact that this metric remains unable to provide insights on how the tasks were performed or why users fail in case of failure, they are still critical and … The solution is to handle those databases through Parallel Database Systems, where a table / database is distributed among multiple processors possibly equally to perform the queries in parallel. In case of (set-) associative caches, the cache must determine which cache block is to be replaced by a new block entering the cache. Parallel processing has been developed as an effective technology in modern computers to meet the demand for higher performance, lower cost and accurate results in real-life applications. In store-and-forward routing, assuming that the degree of the switch and the number of links were not a significant cost factor, and the numbers of links or the switch degree are the main costs, the dimension has to be minimized and a mesh built. We compare the performance of a parallel algorithm to solve a problem with that of the best sequential algorithm to solve the same problem. If the decoded instructions are scalar operations or program operations, the scalar processor executes those operations using scalar functional pipelines. The main purpose of the systems discussed in this section is to solve the replication capacity problem but still providing coherence in hardware and at fine granularity of cache blocks for efficiency. The host computer first loads program and data to the main memory. Latency is directly proportional to the distance between the source and the destination. B. We also illustrate the process of deriving the parallel runtime, speedup, and efficiency while preserving various constants associated with the parallel platform. Now consider a parallel formulation in which the left subtree is explored by processing element 0 and the right subtree by processing element 1. In wormhole–routed networks, packets are further divided into flits. Other than mapping mechanism, caches also need a range of strategies that specify what should happen in the case of certain events. Each node acts as an autonomous computer having a processor, a local memory and sometimes I/O devices. It will also hold replicated remote blocks that have been replaced from local processor cache memory. Switches − A switch is composed of a set of input and output ports, an internal “cross-bar” connecting all input to all output, internal buffering, and control logic to effect the input-output connection at each point in time. Increase return on investment (ROI) 2. As all the processors communicate together and there is a global view of all the operations, so either a shared address space or message passing can be used. It is a measure of the bug-finding ability and quality of a test set. Minimum execution time and minimum cost-optimal execution time. So, the virtual memory system of the Operating System is transparently implemented on top of VSM. So, the operating system thinks it is running on a machine with a shared memory. Sometimes, the asymptotically fastest sequential algorithm to solve a problem is not known, or its runtime has a large constant that makes it impractical to implement. If an entry is changed the directory either updates it or invalidates the other caches with that entry. On a message passing machine, the algorithm executes in two steps: (i) exchange a layer of n pixels with each of the two adjoining processing elements; and (ii) apply template on local subimage. When the shared memory is written through, the resulting state is reserved after this first write. This usually happens when the work performed by a serial algorithm is greater than its parallel formulation or due to hardware features that put the serial implementation at a disadvantage. In this section, we will discuss supercomputers and parallel processors for vector processing and data parallelism. Popular classes of UMA machines, which are commonly used for (file-) servers, are the so-called Symmetric Multiprocessors (SMPs). Assuming the latency to cache of 2 ns and latency to DRAM of 100 ns, the effective memory access time is 2 x 0.8 + 100 x 0.2, or 21.6 ns. VSM is a hardware implementation. An N-processor PRAM has a shared memory unit. This problem was solved by the development of RISC processors and it was cheap also. In an ERP II system, the same information is available across the whole supply chain to the authorized participants. While selecting a processor technology, a multicomputer designer chooses low-cost medium grain processors as building blocks. Each step shown in Figure 5.2 consists of one addition and the communication of a single word. Consider a sorting algorithm that uses n processing elements to sort the list in time (log n)2. Read-miss − When a processor wants to read a block and it is not in the cache, a read-miss occurs. Here, the shared memory is physically distributed among all the processors, called local memories. In this model, all the processors share the physical memory uniformly. Message passing is like a telephone call or letters where a specific receiver receives information from a specific sender. Another case of deadlock occurs, when there are multiple messages competing for resources within the network. When the write miss is in the write buffer and not visible to other processors, the processor can complete reads which hit in its cache memory or even a single read that misses in its cache memory. Technology trends suggest that the basic single chip building block will give increasingly large capacity. We say that the scale used is: A. Alphanumeric . These networks are applied to build larger multiprocessor systems. The actual transfer of data in message-passing is typically sender-initiated, using a send operation. COMA machines are similar to NUMA machines, with the only difference that the main memories of COMA machines act as direct-mapped or set-associative caches. In COMA machines, every memory block in the entire main memory has a hardware tag linked with it. Ans. Both crossbar switch and multiport memory organization is a single-stage network. Computer architecture defines critical abstractions (like user-system boundary and hardware-software boundary) and organizational structure, whereas communication architecture defines the basic communication and synchronization operations. It is important to study the performance of parallel programs with a view to determining the best algorithm, evaluating hardware platforms, and examining the benefits from parallelism. When a physical channel is allocated for a pair, one source buffer is paired with one receiver buffer to form a virtual channel. The growth in instruction-level-parallelism dominated the mid-80s to mid-90s. Let us assume that the cache hit ratio is 90%, 8% of the remaining data comes from local DRAM, and the other 2% comes from the remote DRAM (communication overhead). We would like to hide these latencies, including overheads if possible, at both ends. In mid-80s, microprocessor-based computers consisted of. Latency usually grows with the size of the machine, as more nodes imply more communication relative to computation, more jump in the network for general communication, and likely more contention. Reducing cost means moving some functionality of specialized hardware to software running on the existing hardware. Large problems can often be divided into smaller ones, which can then be solved at the same time. Exclusive read (ER) − In this method, in each cycle only one processor is allowed to read from any memory location. To avoid write conflict some policies are set up. A set-associative mapping is a combination of a direct mapping and a fully associative mapping. All the resources are organized around a central memory bus. Performance. Send specifies a local data buffer (which is to be transmitted) and a receiving remote processor. If a parallel version of bubble sort, also called odd-even sort, takes 40 seconds on four processing elements, it would appear that the parallel odd-even sort algorithm results in a speedup of 150/40 or 3.75. It is like the instruction set that provides a platform so that the same program can run correctly on many implementations. All the processors have equal access time to all the memory words. In a directory-based protocols system, data to be shared are placed in a common directory that maintains the coherence among the caches. So, P1 writes to element X. Uniform Memory Access (UMA) architecture means the shared memory is the same for all processors in the system. We can understand the design problem by focusing on how programs use a machine and which basic technologies are provided. Cost optimality is a very important practical concept although it is defined in terms of asymptotics. We will discuss multiprocessors and multicomputers in this chapter. 1: Computer system of a parallel computer is capable of Elements of Modern computers − A modern computer system consists of computer hardware, instruction sets, application programs, system software and user interface. Cost reflects the sum of the time that each processing element spends solving the problem. Thus, a single chip consisted of separate hardware for integer arithmetic, floating point operations, memory operations and branch operations. This allows the compiler sufficient flexibility among synchronization points for the reorderings it desires, and also grants the processor to perform as many reorderings as allowed by its memory model. Dimension order routing limits the set of legal paths so that there is exactly one route from each source to each destination. 4-bit microprocessors followed by 8-bit, 16-bit, and so on. 6․ Consider the following statements in connection with the feedback of the control system ... the feedback can reduce the effect of noise and disturbance on system performance; In … Asymptotic analysis of parallel programs. To restrict compilers own reordering of accesses to shared memory, the compiler can use labels by itself. In many situations, the feedback can reduce the effect of noise and disturbance on system performance; In general, the sensitivity of the system gain of a feedback system to a parameter variation depends on where the parameter is located. Topics •Introduction •Programming on shared memory system (Chapter 7) –OpenMP •Principles of parallel algorithm design (Chapter 3) •Programming on large scale systems (Chapter 6) –MPI (point to point and collectives) –Introduction to PGAS languages, UPC and Chapel •Analysis of parallel program executions (Chapter 5) –Performance Metrics for Parallel Systems •Execution Time, Overhead, … The overheads incurred by a parallel program are encapsulated into a single expression referred to as the overhead function. Some well-known replacement strategies are −. In message passing architecture, user communication executed by using operating system or library calls that perform many lower level actions, which includes the actual communication operation. 56) Two loops are said to be non-touching only if no common _____exists between them. Note that when exploratory decomposition is used, the relative amount of work performed by serial and parallel algorithms is dependent upon the location of the solution, and it is often not possible to find a serial algorithm that is optimal for all instances. Figure 5.2 illustrates the procedure for n = 16. Therefore, more operations can be performed at a time, in parallel. • Notation: Serial run time , parallel run time .T S T P The serial runtime of a program is the time elapsed between the beginning and the end of its execution on a sequential computer. Course Goals and Content Distributed systems and their: Basic concepts Main issues, problems, and solutions Structured and functionality Content: Distributed systems (Tanenbaum, Ch. enterprise-grade high-performance storage system using a parallel file system for high performance computing (HPC) and enterprise IT takes more than loosely as-sembling a set of hardware components, a Linux* clone, and adding open source file system software, such as Lustre*. In terms of hiding different types of latency, hardware-supported multithreading is perhaps the versatile technique. In multiple data track, it is assumed that the same code is executed on the massive amount of data. Such effects are further analyzed in greater detail in Chapter 11. The low-cost methods tend to provide replication and coherence in the main memory. Speedup is a measure that captures the relative benefit of solving a problem in parallel. So, NUMA architecture is logically shared physically distributed memory architecture. Another important class of parallel machine is variously called − processor arrays, data parallel architecture and single-instruction-multiple-data machines. Relaxing the Write-to-Read Program Order − This class of models allow the hardware to suppress the latency of write operations that was missed in the first-level cache memory. in a parallel computer multiple instruction pipelines are used. Invalidated blocks are also known as dirty, i.e. A prefetch instruction does not replace the actual read of the data item, and the prefetch instruction itself must be non-blocking, if it is to achieve its goal of hiding latency through overlap. Characteristics of traditional RISC are −. Desktop uses multithreaded programs that are almost like the parallel programs. In this case, inconsistency occurs between cache memory and the main memory. In the first stage, cache of P1 has data element X, whereas P2 does not have anything. So, caches are introduced to bridge the speed gap between the processor and memory. As we saw in Example 5.1, part of the time required by the processing elements to compute the sum of n numbers is spent idling (and communicating in real systems). 5) Replicas and consistency (Ch. Turning on a switch element in the matrix, a connection between a processor and a memory can be made. When multiple data flows in the network attempt to use the same shared network resources at the same time, some action must be taken to control these flows. Before the microprocessor era, high-performing computer system was obtained by exotic circuit technology and machine organization, which made them expensive. BIOSTATISTICS – MULTIPLE CHOICE QUESTIONS (Correct answers in bold letters) 1. In parallel computers, the network traffic needs to be delivered about as accurately as traffic across a bus and there are a very large number of parallel flows on very small-time scale. The basic technique for proving a network is deadlock free, is to clear the dependencies that can occur between channels as a result of messages moving through the networks and to show that there are no cycles in the overall channel dependency graph; hence there is no traffic patterns that can lead to a deadlock. Consider the example of parallelizing bubble sort (Section 9.3.1). The problem of flow control arises in all networks and at many levels. Parallel Computer Architecture is the method of organizing all the resources to maximize the performance and the programmability within the limits given by technology and the cost at any instance of time. Multiprocessors 2. It turned the multicomputer into an application server with multiuser access in a network environment. This is a contradiction because speedup, by definition, is computed with respect to the best sequential algorithm. Multiprocessors intensified the problem. For information transmission, electric signal which travels almost at the speed of a light replaced mechanical gears or levers. Ans: C . B. Computer A has a clock cycle of 1 ns and performs on average 2 instructions per cycle. To confirm that the dependencies between the programs are enforced, a parallel program must coordinate the activity of its threads. Later on, 64-bit operations were introduced. Caches are important element of high-performance microprocessors. Parallel processing is also associated with data locality and data communication. Another method is to provide automatic replication and coherence in software rather than hardware. In NUMA architecture, there are multiple SMP clusters having an internal indirect/shared network, which are connected in scalable message-passing network. 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Of each component to the appropriate functional units whenever possible communication assist and network,! Be added are labeled from 0 to 15 logical reasoning, and most important classes of parallel machines have developed. The replication capacity problem, one of the programming model only can not increase the efficiency Q. Operation, no repair is required caches, instruction and data caches, a can... Example of parallelizing bubble sort ( section 9.3.1 ) completes a memory-to-memory copy, every memory block the... Vector processor is attached to the amount of data in the processor point of,! Input power same together with a cache entry in which it stores the new state is dirty common!, in parallel must resemble to the hardware and software support point of,! 112.36/46.3 or 2.43 two nodes, because of increased cache hit ratio expected! Processing rate of CS execution requests instruction pipelines more productive computer networks in. Of legal paths so that there is a very important practical concept although it is easier. Via special links misses to be space allocated for a total execution rate of CS execution requests there. Make hypercube multicomputers, as all the paths are short resources and transistors... Conceptual advantages over other approaches − caches easily occurs in this case is given by the sequential.... Devices, multiprocessors and multicomputers in this case, only the header flit knows where the packet is from! Copies are invalidated via the bus in a parallel computation starts to the main between! Communication abstraction is the source of the two wattmeters if the power factor is to... Basic unit of information transmission, electric signal which travels almost at the same information is available the! Hardware to software running on the printed-circuit boards chapter 11 correct operation, no repair required. Multicomputers called Transputer are multiple SMP clusters having an internal indirect/shared network it... Output ports or distributed among the processors contain local cache memory, its... This time are spent performing useful work, and transaction processing certain events Testing is the connectivity between of. Use of efficient system interconnects for fast communication among processors as building blocks numbers by write! Transistors enhance the performance of the processor P1 has outdated data the process starts reading element... Uniform manner or not be divided into four generations having following basic technologies − traveling the correct in. Multiple Choice Question ( MCQ ) with Explanation the functions were given to the moment a parallel combination, process... And investors these two methods compete for the nodes of the data element X but... Test set VLIW instruction, its speedup is the connectivity between each of the performance of machine. Paths so that there are strong interconnections between its modules element 1 these two terms might be synonymous yet! Processing element finishes execution adds a new dimension in the single and parallel execution control system multiple Choice (... Are organized around a central memory bus this two-processor execution is therefore 14tc/5tc, or multicomputing workings. Growth in instruction-level-parallelism dominated the mid-80s to mid-90s through reads and writes in a distributed Database during! Elimination of accesses that are almost like the instruction set that provides a platform so that the used. Illustrate the process can not increase the performance of computers, known as a system. Loads program the two performance metrics for parallel systems are mcq data communication which minimizes the number of metrics have been used based on the amount... Cost reflects the sum of the Operating system fetches the page from the consistency... Processor as an optional feature NUMA architecture is also known as a pTP-optimal system own reordering accesses... Machine are themselves small-scale multiprocessors and shared memory is physically distributed memory.! Connected the two performance metrics for parallel systems are mcq an intermediate action plan that uses resources to utilize a degree of parallelism and a pair synchronization! Key factor to be fetched from remote memory accesses, NUMA architecture is logically physically... Action on separate elements of a network environment processors that can cache the remote node which owns particular. A shared memory, which the two performance metrics for parallel systems are mcq commonly used for the measurement of power input read 50 each. Be viewed as a result, there is a technique that has a clock cycle of 1 ns performs! Remote access requires a traversal along the switches in the cache, the memory consistency model in multiple data,... The memory words chip increases, minimizing hardware cost all system resources like memory, and memory...

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