Parallel Processing & Pipelining in Computer Architecture_Prof.Sumalatha.pptx

Parallel Processing and Pipelining

1. Computer Architecture Parallel Processing By, Prof. Sumalatha A

2. Parallel Processing Parallel processing is an efficient form of information processing which emphasizes the exploitation of concurrent events in the computing process. Parallel Processing demands concurrent execution of many programs in the computer. Concurrency implies parallelism, simultaneity, and pipelining.

3. Introduction to Parallelism in Uniprocessor S ystem From an operating point of view, computer systems have improved chronologically in four phases:  batch processing  multiprogramming   time-sharing multiprocessing In these four operating modes, the degree of parallelism increase sharply from phase to phase.

4. Introduction to Parallelism in Uniprocessor System Contd … We define parallel processing as an efficient form of information processing that emphasizes the exploitation of concurrent events in the computing process. Parallel Processing demands the concurrent execution of many programs in the computer. Concurrency implies parallelism, simultaneity, and pipelining. The highest level of parallel processing is conducted among multiple jobs or programs through multiprogramming, time-sharing, and multiprocessing. Parallel processing can be challenged in four programmatic levels: Job or program level – the highest level of parallel processing conducted among multiple jobs or programs  Task or procedure level – next higher level parallel processing conducted among procedures or tasks within the same program   Inter-instruction level- The third level to exploit concurrency among multiple instructions   Intra-instruction level-Finally concurrent operations within each instruction

5. Basic Uniprocessor Architecture A typical uniprocessor computer consists of three major components the main memory, the CPU ( Central Processing Unit ), and the I/O(Input-Output) subsystem .   There are two architectures of commercially available uniprocessor computers to show the relation between three subsystems

6. System Architecture of the Super mini VAX-11/780 uniprocessor system

7. System Architecture of the Super mini VAX-11/780 uniprocessor system Contd … There are 16, 32-bit general purpose registers one of which is a Program Counter (PC ). There is also a special CPU status register containing about the current state of the processor is executed . The CPU contains an ALU with an optional Floating-point accelerator and some local cache memory with an optional diagnostic memory. Floating-point accelerator (FPA) -A device to improve the overall performance of a computer by removing the burden of performing floating-point arithmetic from the central processor. optional diagnostic memory –checks the errors.  

8. The CPU can be intervened by the operator through the console connected to a floppy disk. The CPU, the main memory( 2^32 words of 32-bit each ), and the I/O subsystem are all connected to a common bus, the synchronous backplane interconnection(SBI). Through this bus, all I/O devices can communicate with each other with the CPU or with the memory. I/O devices can be connected directly to the SBI through the unibus and its controller or through a mass bus and its controller System Architecture of the Super mini VAX-11/780 uniprocessor system Contd …

9. System Architecture of the mainframe IBM system 370/model 168 uniprocessor computer

10. The CPU contains the instruction decoding and execution units as well as the cache . Main memory is divided into four units referred to as logical storage units (LSU) that are four ways interleaved . The storage controller provides multiport Connections between the CPU and the four LSUs . Peripherals are connected to the system via high-speed I/O channels which operate asynchronously with the CPU System Architecture of the mainframe IBM system 370/model 168 uniprocessor computer C ontd …

11. Parallelism Parallelism can be promoted by Hardware means Software means

12. PARALLELLISM IN UNIPROCESSOR SYSTEM A number of parallel processing mechanisms have been developed in uniprocessor computers. We identify them in the following six categories: 1.Multiplicity of functional units 2.Parallelism and pipelining within the CPU 3.Overlapped CPU and I/O operations 4.Use of a hierarchical memory system 5.Balancing of subsystem bandwidths 6.Multiprogramming and time sharing

13. Multiplicity of Functional U nits Early computers   - one ALU that performs one operation at a time - Slow processing Multiple and specialized functional units . - operate in parallel.  -  two parallel execution units (fixed and floating point arithmetic ) in CDC-6600    →10 functional units

14. System Architecture of CDC-6600

15. Parallelism and pipelining within the CPU Instead of serial bit adders, parallel adders are used in almost ALUs Use of High-speed multiplier recoding and convergence division Sharing of hardware resources for functions of multiply and divide Various phases of instructions executions (instruction fetch , decode, operand fetch, arithmetic logic execution, store result) are pipelined For overlapped instruction executions, instruction prefetch and buffering techniques have been developed .

16. Overlapped CPU and I/O operations I/O operations are performed simultaneously with CPU computations by using separate I/O controllers, channels, or I/O processors. DMA channel can be used for direct transfer of data between main memory and I/O devices

17. Use of a hierarchical memory system CPU is 1000 times faster than memory access An hierarchical memory system can be used to close up the speed gap Cache memory can be used to be served as a buffer between CPU and main memory

18. Balancing of subsystem bandwidths CPU is the fastest unit in computer. The bandwidth of a system is defined as the number of operations performed per unit time. In case of main memory the memory bandwidth is measured by the number of words that can be accessed per unit time. Relationship b/w BWs

19. Balancing of subsystem bandwidths Bandwidth Balancing Between CPU and Memory The speed gap between the CPU and the main memory can be closed up by using fast cache memory between them. A block of memory words is moved from the main memory into the cache so that immediate instructions can be available most of the time from the cache. Bandwidth Balancing Between Memory and I/O Devices Input-output channels with different speeds can be used between the slow I/O devices and the main memory. The I/O channels perform buffering and multiplexing functions to transfer the data from multiple disks into the main memory by stealing cycles from the CPU .

20. Parallel Computer Structures A parallel computer is a kind of computer structure where a large complex problem is broken into multiple small problems which are then executed simultaneously by several processors. We often consider this as parallel processing. It is divided into three Pipeline Computer Array Processors Multiprocessor Systems

21. Pipeline Computer Pipeline computers leverage parallel computing by overlapping the execution of one process with another process. If we consider executing a small program that has a set of instructions then we can categorize the execution of the entire program in four steps that must be repeated continuously till the last instruction in the program gets executed. The four steps we mentioned above are instruction fetching (IF), instruction decoding (ID), operand fetch (OF), and instruction execution (IE). Each instruction of the program is fetched from the main memory, it is decoded by the processor, and the operands mentioned in the instructions that are required for the execution of instruction are fetched from the main memory, and at last, the instruction is executed.

22. Space-Time Diagram for Non-Pipelined Processor The figure below shows that to execute three instructions completely it takes 12 secs.

23. And if we implement pipelining then instruction will be executed in an overlapped fashion. As you can see that the four instructions can be executed in 7 sec. Pipeline computer synchronizes operations of all stages under a common clock. Hence, we can say that executing instructions in pipelined fashion is more efficient. Space-Time Diagram for Non-Pipelined Processor Contd …