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Parallel Processing Techniques Pipelining

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RNShukla7

This document discusses parallel processing techniques in computer systems including pipelining and vector processing. It covers parallel computer architectures such as SISD, SIMD, MISD, and MIMD systems. The document also describes pipelining techniques including arithmetic pipelining and instruction pipelining. It discusses hazards that can occur in pipelined systems such as structural hazards, data hazards, and control hazards as well as methods to address these hazards including forwarding, interlocking, and instruction scheduling.

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1 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PIPELINING AND VECTOR PROCESSING • Parallel Processing • Pipelining • Arithmetic Pipeline • Instruction Pipeline • RISC Pipeline • Vector Processing • Array Processors
2 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PARALLEL PROCESSING Levels of Parallel Processing - Job or Program level - Task or Procedure level - Inter-Instruction level - Intra-Instruction level Execution of Concurrent Events in the computing process to achieve faster Computational Speed Parallel Processing
3 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PARALLEL COMPUTERS Architectural Classification Number of Data Streams Number of Instruction Streams Single Multiple Single Multiple SISD SIMD MISD MIMD Parallel Processing – Flynn's classification » Based on the multiplicity of Instruction Streams and Data Streams » Instruction Stream • Sequence of Instructions read from memory » Data Stream • Operations performed on the data in the processor
4 Pipelining and Vector Processing Computer Organization Computer Architectures Lab COMPUTER ARCHITECTURES FOR PARALLEL PROCESSING Von-Neuman based Dataflow Reduction SISD MISD SIMD MIMD Superscalar processors Superpipelined processors VLIW Nonexistence Array processors Systolic arrays Associative processors Shared-memory multiprocessors Bus based Crossbar switch based Multistage IN based Message-passing multicomputers Hypercube Mesh Reconfigurable Parallel Processing
5 Pipelining and Vector Processing Computer Organization Computer Architectures Lab SISD COMPUTER SYSTEMS Control Unit Processor Unit Memory Instruction stream Data stream Characteristics - Standard von Neumann machine - Instructions and data are stored in memory - One operation at a time Limitations Von Neumann bottleneck Maximum speed of the system is limited by the Memory Bandwidth (bits/sec or bytes/sec) - Limitation on Memory Bandwidth - Memory is shared by CPU and I/O Parallel Processing
6 Pipelining and Vector Processing Computer Organization Computer Architectures Lab SISD PERFORMANCE IMPROVEMENTS • Multiprogramming • Spooling • Multifunction processor • Pipelining • Exploiting instruction-level parallelism - Superscalar - Superpipelining - VLIW (Very Long Instruction Word) Parallel Processing
7 Pipelining and Vector Processing Computer Organization Computer Architectures Lab MISD COMPUTER SYSTEMS M CU P M CU P M CU P • • • • • • Memory Instruction stream Data stream Characteristics - There is no computer at present that can be classified as MISD Parallel Processing
8 Pipelining and Vector Processing Computer Organization Computer Architectures Lab SIMD COMPUTER SYSTEMS Control Unit Memory Alignment network P P P • • • M M M • • • Data bus Instruction stream Data stream Processor units Memory modules Characteristics - Only one copy of the program exists - A single controller executes one instruction at a time Parallel Processing
9 Pipelining and Vector Processing Computer Organization Computer Architectures Lab TYPES OF SIMD COMPUTERS Array Processors - The control unit broadcasts instructions to all PEs, and all active PEs execute the same instructions - ILLIAC IV, GF-11, Connection Machine, DAP, MPP Systolic Arrays - Regular arrangement of a large number of very simple processors constructed on VLSI circuits - CMU Warp, Purdue CHiP Associative Processors - Content addressing - Data transformation operations over many sets of arguments with a single instruction - STARAN, PEPE Parallel Processing
10 Pipelining and Vector Processing Computer Organization Computer Architectures Lab MIMD COMPUTER SYSTEMS Interconnection Network P M P M P M • • • Shared Memory Characteristics - Multiple processing units - Execution of multiple instructions on multiple data Types of MIMD computer systems - Shared memory multiprocessors - Message-passing multicomputers Parallel Processing
11 Pipelining and Vector Processing Computer Organization Computer Architectures Lab SHARED MEMORY MULTIPROCESSORS Characteristics All processors have equally direct access to one large memory address space Example systems Bus and cache-based systems - Sequent Balance, Encore Multimax Multistage IN-based systems - Ultracomputer, Butterfly, RP3, HEP Crossbar switch-based systems - C.mmp, Alliant FX/8 Limitations Memory access latency Hot spot problem Interconnection Network(IN) • • • • • • P P P M M M Buses, Multistage IN, Crossbar Switch Parallel Processing
12 Pipelining and Vector Processing Computer Organization Computer Architectures Lab MESSAGE-PASSING MULTICOMPUTER Characteristics - Interconnected computers - Each processor has its own memory, and communicate via message-passing Example systems - Tree structure: Teradata, DADO - Mesh-connected: Rediflow, Series 2010, J-Machine - Hypercube: Cosmic Cube, iPSC, NCUBE, FPS T Series, Mark III Limitations - Communication overhead - Hard to programming Message-Passing Network • • • P P P M M M • • • Point-to-point connections Parallel Processing
13 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PIPELINING R1  Ai, R2  Bi Load Ai and Bi R3  R1 * R2, R4  Ci Multiply and load Ci R5  R3 + R4 Add A technique of decomposing a sequential process into suboperations, with each subprocess being executed in a partial dedicated segment that operates concurrently with all other segments. Ai * Bi + Ci for i = 1, 2, 3, ... , 7 Ai R1 R2 Multiplier R3 R4 Adder R5 Memory Pipelining Bi Ci Segment 1 Segment 2 Segment 3
14 Pipelining and Vector Processing Computer Organization Computer Architectures Lab OPERATIONS IN EACH PIPELINE STAGE Clock Pulse Segment 1 Segment 2 Segment 3 Number R1 R2 R3 R4 R5 1 A1 B1 2 A2 B2 A1 * B1 C1 3 A3 B3 A2 * B2 C2 A1 * B1 + C1 4 A4 B4 A3 * B3 C3 A2 * B2 + C2 5 A5 B5 A4 * B4 C4 A3 * B3 + C3 6 A6 B6 A5 * B5 C5 A4 * B4 + C4 7 A7 B7 A6 * B6 C6 A5 * B5 + C5 8 A7 * B7 C7 A6 * B6 + C6 9 A7 * B7 + C7 Pipelining
15 Pipelining and Vector Processing Computer Organization Computer Architectures Lab GENERAL PIPELINE General Structure of a 4-Segment Pipeline S R 1 1 S R 2 2 S R 3 3 S R 4 4 Input Clock Space-Time Diagram 1 2 3 4 5 6 7 8 9 T1 T1 T1 T1 T2 T2 T2 T2 T3 T3 T3 T3 T4 T4 T4 T4 T5 T5 T5 T5 T6 T6 T6 T6 Clock cycles Segment 1 2 3 4 Pipelining
16 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PIPELINE SPEEDUP n: Number of tasks to be performed Conventional Machine (Non-Pipelined) tn: Clock cycle t1: Time required to complete the n tasks t1 = n * tn Pipelined Machine (k stages) tp: Clock cycle (time to complete each suboperation) tk: Time required to complete the n tasks tk = (k + n - 1) * tp Speedup Sk: Speedup Sk = n*tn / (k + n - 1)*tp n   Sk = tn tp ( = k, if tn = k * tp ) lim Pipelining
17 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PIPELINE AND MULTIPLE FUNCTION UNITS P1 I i P2 Ii+1 P3 I i+2 P4 I i+3 Multiple Functional Units Example - 4-stage pipeline - subopertion in each stage; tp = 20nS - 100 tasks to be executed - 1 task in non-pipelined system; 20*4 = 80nS Pipelined System (k + n - 1)*tp = (4 + 99) * 20 = 2060nS Non-Pipelined System n*k*tp = 100 * 80 = 8000nS Speedup Sk = 8000 / 2060 = 3.88 4-Stage Pipeline is basically identical to the system with 4 identical function units Pipelining
18 Pipelining and Vector Processing Computer Organization Computer Architectures Lab ARITHMETIC PIPELINE Floating-point adder [1] Compare the exponents [2] Align the mantissa [3] Add/sub the mantissa [4] Normalize the result X = A x 2a Y = B x 2b R Compare exponents by subtraction a b R Choose exponent Exponents R A B Align mantissa Mantissas Difference R Add or subtract mantissas R Normalize result R R Adjust exponent R Segment 1: Segment 2: Segment 3: Segment 4: Arithmetic Pipeline
19 Pipelining and Vector Processing Computer Organization Computer Architectures Lab 4-STAGE FLOATING POINT ADDER A = a x 2p B = b x 2q p a q b Exponent subtractor Fraction selector Fraction with min(p,q) Right shifter Other fraction t = |p - q| r = max(p,q) Fraction adder Leading zero counter r c Left shifter c Exponent adder r s d d Stages: S1 S2 S3 S4 C = A + B = c x 2 = d x 2 r s (r = max (p,q), 0.5  d < 1) Arithmetic Pipeline
20 Pipelining and Vector Processing Computer Organization Computer Architectures Lab INSTRUCTION CYCLE Six Phases* in an Instruction Cycle [1] Fetch an instruction from memory [2] Decode the instruction [3] Calculate the effective address of the operand [4] Fetch the operands from memory [5] Execute the operation [6] Store the result in the proper place * Some instructions skip some phases * Effective address calculation can be done in the part of the decoding phase * Storage of the operation result into a register is done automatically in the execution phase ==> 4-Stage Pipeline [1] FI: Fetch an instruction from memory [2] DA: Decode the instruction and calculate the effective address of the operand [3] FO: Fetch the operand [4] EX: Execute the operation Instruction Pipeline
21 Pipelining and Vector Processing Computer Organization Computer Architectures Lab INSTRUCTION PIPELINE Execution of Three Instructions in a 4-Stage Pipeline Instruction Pipeline FI DA FO EX FI DA FO EX FI DA FO EX i i+1 i+2 Conventional Pipelined FI DA FO EX FI DA FO EX FI DA FO EX i i+1 i+2
22 Pipelining and Vector Processing Computer Organization Computer Architectures Lab INSTRUCTION EXECUTION IN A 4-STAGE PIPELINE 1 2 3 4 5 6 7 8 9 10 12 13 11 FI DA FO EX 1 FI DA FO EX FI DA FO EX FI DA FO EX FI DA FO EX FI DA FO EX FI DA FO EX 2 3 4 5 6 7 FI Step: Instruction (Branch) Instruction Pipeline Fetch instruction from memory Decode instruction and calculate effective address Branch? Fetch operand from memory Execute instruction Interrupt? Interrupt handling Update PC Empty pipe no yes yes no Segment1: Segment2: Segment3: Segment4:
23 Pipelining and Vector Processing Computer Organization Computer Architectures Lab MAJOR HAZARDS IN PIPELINED EXECUTION Structural hazards(Resource Conflicts) Hardware Resources required by the instructions in simultaneous overlapped execution cannot be met Data hazards (Data Dependency Conflicts) An instruction scheduled to be executed in the pipeline requires the result of a previous instruction, which is not yet available JMP ID PC + PC bubble IF ID OF OE OS Branch address dependency Hazards in pipelines may make it necessary to stall the pipeline Pipeline Interlock: Detect Hazards Stall until it is cleared Instruction Pipeline ADD DA B,C + INC DA +1 R1 bubble Data dependency R1 <- B + C R1 <- R1 + 1 Control hazards Branches and other instructions that change the PC make the fetch of the next instruction to be delayed
24 Pipelining and Vector Processing Computer Organization Computer Architectures Lab STRUCTURAL HAZARDS Structural Hazards Occur when some resource has not been duplicated enough to allow all combinations of instructions in the pipeline to execute Example: With one memory-port, a data and an instruction fetch cannot be initiated in the same clock The Pipeline is stalled for a structural hazard <- Two Loads with one port memory -> Two-port memory will serve without stall Instruction Pipeline FI DA FO EX i i+1 i+2 FI DA FO EX FI DA FO EX stall stall
25 Pipelining and Vector Processing Computer Organization Computer Architectures Lab DATA HAZARDS Data Hazards Occurs when the execution of an instruction depends on the results of a previous instruction ADD R1, R2, R3 SUB R4, R1, R5 Hardware Technique Interlock - hardware detects the data dependencies and delays the scheduling of the dependent instruction by stalling enough clock cycles Forwarding (bypassing, short-circuiting) - Accomplished by a data path that routes a value from a source (usually an ALU) to a user, bypassing a designated register. This allows the value to be produced to be used at an earlier stage in the pipeline than would otherwise be possible Software Technique Instruction Scheduling(compiler) for delayed load Data hazard can be dealt with either hardware techniques or software technique Instruction Pipeline
26 Pipelining and Vector Processing Computer Organization Computer Architectures Lab FORWARDING HARDWARE Register file Result write bus Bypass path ALU result buffer MUX ALU R4 MUX Instruction Pipeline Example: ADD R1, R2, R3 SUB R4, R1, R5 3-stage Pipeline I: Instruction Fetch A: Decode, Read Registers, ALU Operations E: Write the result to the destination register I A E ADD SUB I A E Without Bypassing I A E SUB With Bypassing
27 Pipelining and Vector Processing Computer Organization Computer Architectures Lab INSTRUCTION SCHEDULING a = b + c; d = e - f; Unscheduled code: Delayed Load A load requiring that the following instruction not use its result Scheduled Code: LW Rb, b LW Rc, c LW Re, e ADD Ra, Rb, Rc LW Rf, f SW a, Ra SUB Rd, Re, Rf SW d, Rd LW Rb, b LW Rc, c ADD Ra, Rb, Rc SW a, Ra LW Re, e LW Rf, f SUB Rd, Re, Rf SW d, Rd Instruction Pipeline
28 Pipelining and Vector Processing Computer Organization Computer Architectures Lab CONTROL HAZARDS Branch Instructions - Branch target address is not known until the branch instruction is completed - Stall -> waste of cycle times FI DA FO EX FI DA FO EX Branch Instruction Next Instruction Target address available Dealing with Control Hazards * Prefetch Target Instruction * Branch Target Buffer * Loop Buffer * Branch Prediction * Delayed Branch Instruction Pipeline
29 Pipelining and Vector Processing Computer Organization Computer Architectures Lab CONTROL HAZARDS Instruction Pipeline Prefetch Target Instruction – Fetch instructions in both streams, branch not taken and branch taken – Both are saved until branch branch is executed. Then, select the right instruction stream and discard the wrong stream Branch Target Buffer(BTB; Associative Memory) – Entry: Addr of previously executed branches; Target instruction and the next few instructions – When fetching an instruction, search BTB. – If found, fetch the instruction stream in BTB; – If not, new stream is fetched and update BTB Loop Buffer(High Speed Register file) – Storage of entire loop that allows to execute a loop without accessing memory Branch Prediction – Guessing the branch condition, and fetch an instruction stream based on the guess. Correct guess eliminates the branch penalty Delayed Branch – Compiler detects the branch and rearranges the instruction sequence by inserting useful instructions that keep the pipeline busy in the presence of a branch instruction
30 Pipelining and Vector Processing Computer Organization Computer Architectures Lab RISC PIPELINE Instruction Cycles of Three-Stage Instruction Pipeline RISC Pipeline RISC - Machine with a very fast clock cycle that executes at the rate of one instruction per cycle <- Simple Instruction Set Fixed Length Instruction Format Register-to-Register Operations Data Manipulation Instructions I: Instruction Fetch A: Decode, Read Registers, ALU Operations E: Write a Register Load and Store Instructions I: Instruction Fetch A: Decode, Evaluate Effective Address E: Register-to-Memory or Memory-to-Register Program Control Instructions I: Instruction Fetch A: Decode, Evaluate Branch Address E: Write Register(PC)
31 Pipelining and Vector Processing Computer Organization Computer Architectures Lab DELAYED LOAD Three-segment pipeline timing Pipeline timing with data conflict clock cycle 1 2 3 4 5 6 Load R1 I A E Load R2 I A E Add R1+R2 I A E Store R3 I A E Pipeline timing with delayed load clock cycle 1 2 3 4 5 6 7 Load R1 I A E Load R2 I A E NOP I A E Add R1+R2 I A E Store R3 I A E LOAD: R1  M[address 1] LOAD: R2  M[address 2] ADD: R3  R1 + R2 STORE: M[address 3]  R3 RISC Pipeline The data dependency is taken care by the compiler rather than the hardware
32 Pipelining and Vector Processing Computer Organization Computer Architectures Lab DELAYED BRANCH 1 I 3 4 6 5 2 Clock cycles: 1. Load A 2. Increment 4. Subtract 5. Branch to X 7 3. Add 8 6. NOP E I A E I A E I A E I A E I A E 9 10 7. NOP 8. Instr. in X I A E I A E 1 I 3 4 6 5 2 Clock cycles: 1. Load A 2. Increment 4. Add 5. Subtract 7 3. Branch to X 8 6. Instr. in X E I A E I A E I A E I A E I A E Compiler analyzes the instructions before and after the branch and rearranges the program sequence by inserting useful instructions in the delay steps Using no-operation instructions Rearranging the instructions RISC Pipeline
33 Pipelining and Vector Processing Computer Organization Computer Architectures Lab VECTOR PROCESSING Vector Processing Vector Processing Applications • Problems that can be efficiently formulated in terms of vectors – Long-range weather forecasting – Petroleum explorations – Seismic data analysis – Medical diagnosis – Aerodynamics and space flight simulations – Artificial intelligence and expert systems – Mapping the human genome – Image processing Vector Processor (computer) Ability to process vectors, and related data structures such as matrices and multi-dimensional arrays, much faster than conventional computers Vector Processors may also be pipelined
34 Pipelining and Vector Processing Computer Organization Computer Architectures Lab VECTOR PROGRAMMING DO 20 I = 1, 100 20 C(I) = B(I) + A(I) Conventional computer Initialize I = 0 20 Read A(I) Read B(I) Store C(I) = A(I) + B(I) Increment I = i + 1 If I  100 goto 20 Vector computer C(1:100) = A(1:100) + B(1:100) Vector Processing
35 Pipelining and Vector Processing Computer Organization Computer Architectures Lab VECTOR INSTRUCTIONS f1: V * V f2: V * S f3: V x V * V f4: V x S * V V: Vector operand S: Scalar operand Type Mnemonic Description (I = 1, ..., n) Vector Processing f1 VSQR Vector square root B(I) * SQR(A(I)) VSIN Vector sine B(I) * sin(A(I)) VCOM Vector complement A(I) * A(I) f2 VSUM Vector summation S * S A(I) VMAX Vector maximum S * max{A(I)} f3 VADD Vector add C(I) * A(I) + B(I) VMPY Vector multiply C(I) * A(I) * B(I) VAND Vector AND C(I) * A(I) . B(I) VLAR Vector larger C(I) * max(A(I),B(I)) VTGE Vector test > C(I) * 0 if A(I) < B(I) C(I) * 1 if A(I) > B(I) f4 SADD Vector-scalar add B(I) * S + A(I) SDIV Vector-scalar divide B(I) * A(I) / S
36 Pipelining and Vector Processing Computer Organization Computer Architectures Lab VECTOR INSTRUCTION FORMAT Operation code Base address source 1 Base address source 2 Base address destination Vector length Vector Processing Vector Instruction Format Source A Source B Multiplier pipeline Adder pipeline Pipeline for Inner Product
37 Pipelining and Vector Processing Computer Organization Computer Architectures Lab MULTIPLE MEMORY MODULE AND INTERLEAVING Vector Processing Multiple Module Memory Address Interleaving Different sets of addresses are assigned to different memory modules AR Memory array DR AR Memory array DR AR Memory array DR AR Memory array DR Address bus Data bus M0 M1 M2 M3

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Parallel Processing Techniques Pipelining

  • 1. 1 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PIPELINING AND VECTOR PROCESSING • Parallel Processing • Pipelining • Arithmetic Pipeline • Instruction Pipeline • RISC Pipeline • Vector Processing • Array Processors
  • 2. 2 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PARALLEL PROCESSING Levels of Parallel Processing - Job or Program level - Task or Procedure level - Inter-Instruction level - Intra-Instruction level Execution of Concurrent Events in the computing process to achieve faster Computational Speed Parallel Processing
  • 3. 3 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PARALLEL COMPUTERS Architectural Classification Number of Data Streams Number of Instruction Streams Single Multiple Single Multiple SISD SIMD MISD MIMD Parallel Processing – Flynn's classification » Based on the multiplicity of Instruction Streams and Data Streams » Instruction Stream • Sequence of Instructions read from memory » Data Stream • Operations performed on the data in the processor
  • 4. 4 Pipelining and Vector Processing Computer Organization Computer Architectures Lab COMPUTER ARCHITECTURES FOR PARALLEL PROCESSING Von-Neuman based Dataflow Reduction SISD MISD SIMD MIMD Superscalar processors Superpipelined processors VLIW Nonexistence Array processors Systolic arrays Associative processors Shared-memory multiprocessors Bus based Crossbar switch based Multistage IN based Message-passing multicomputers Hypercube Mesh Reconfigurable Parallel Processing
  • 5. 5 Pipelining and Vector Processing Computer Organization Computer Architectures Lab SISD COMPUTER SYSTEMS Control Unit Processor Unit Memory Instruction stream Data stream Characteristics - Standard von Neumann machine - Instructions and data are stored in memory - One operation at a time Limitations Von Neumann bottleneck Maximum speed of the system is limited by the Memory Bandwidth (bits/sec or bytes/sec) - Limitation on Memory Bandwidth - Memory is shared by CPU and I/O Parallel Processing
  • 6. 6 Pipelining and Vector Processing Computer Organization Computer Architectures Lab SISD PERFORMANCE IMPROVEMENTS • Multiprogramming • Spooling • Multifunction processor • Pipelining • Exploiting instruction-level parallelism - Superscalar - Superpipelining - VLIW (Very Long Instruction Word) Parallel Processing
  • 7. 7 Pipelining and Vector Processing Computer Organization Computer Architectures Lab MISD COMPUTER SYSTEMS M CU P M CU P M CU P • • • • • • Memory Instruction stream Data stream Characteristics - There is no computer at present that can be classified as MISD Parallel Processing
  • 8. 8 Pipelining and Vector Processing Computer Organization Computer Architectures Lab SIMD COMPUTER SYSTEMS Control Unit Memory Alignment network P P P • • • M M M • • • Data bus Instruction stream Data stream Processor units Memory modules Characteristics - Only one copy of the program exists - A single controller executes one instruction at a time Parallel Processing
  • 9. 9 Pipelining and Vector Processing Computer Organization Computer Architectures Lab TYPES OF SIMD COMPUTERS Array Processors - The control unit broadcasts instructions to all PEs, and all active PEs execute the same instructions - ILLIAC IV, GF-11, Connection Machine, DAP, MPP Systolic Arrays - Regular arrangement of a large number of very simple processors constructed on VLSI circuits - CMU Warp, Purdue CHiP Associative Processors - Content addressing - Data transformation operations over many sets of arguments with a single instruction - STARAN, PEPE Parallel Processing
  • 10. 10 Pipelining and Vector Processing Computer Organization Computer Architectures Lab MIMD COMPUTER SYSTEMS Interconnection Network P M P M P M • • • Shared Memory Characteristics - Multiple processing units - Execution of multiple instructions on multiple data Types of MIMD computer systems - Shared memory multiprocessors - Message-passing multicomputers Parallel Processing
  • 11. 11 Pipelining and Vector Processing Computer Organization Computer Architectures Lab SHARED MEMORY MULTIPROCESSORS Characteristics All processors have equally direct access to one large memory address space Example systems Bus and cache-based systems - Sequent Balance, Encore Multimax Multistage IN-based systems - Ultracomputer, Butterfly, RP3, HEP Crossbar switch-based systems - C.mmp, Alliant FX/8 Limitations Memory access latency Hot spot problem Interconnection Network(IN) • • • • • • P P P M M M Buses, Multistage IN, Crossbar Switch Parallel Processing
  • 12. 12 Pipelining and Vector Processing Computer Organization Computer Architectures Lab MESSAGE-PASSING MULTICOMPUTER Characteristics - Interconnected computers - Each processor has its own memory, and communicate via message-passing Example systems - Tree structure: Teradata, DADO - Mesh-connected: Rediflow, Series 2010, J-Machine - Hypercube: Cosmic Cube, iPSC, NCUBE, FPS T Series, Mark III Limitations - Communication overhead - Hard to programming Message-Passing Network • • • P P P M M M • • • Point-to-point connections Parallel Processing
  • 13. 13 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PIPELINING R1  Ai, R2  Bi Load Ai and Bi R3  R1 * R2, R4  Ci Multiply and load Ci R5  R3 + R4 Add A technique of decomposing a sequential process into suboperations, with each subprocess being executed in a partial dedicated segment that operates concurrently with all other segments. Ai * Bi + Ci for i = 1, 2, 3, ... , 7 Ai R1 R2 Multiplier R3 R4 Adder R5 Memory Pipelining Bi Ci Segment 1 Segment 2 Segment 3
  • 14. 14 Pipelining and Vector Processing Computer Organization Computer Architectures Lab OPERATIONS IN EACH PIPELINE STAGE Clock Pulse Segment 1 Segment 2 Segment 3 Number R1 R2 R3 R4 R5 1 A1 B1 2 A2 B2 A1 * B1 C1 3 A3 B3 A2 * B2 C2 A1 * B1 + C1 4 A4 B4 A3 * B3 C3 A2 * B2 + C2 5 A5 B5 A4 * B4 C4 A3 * B3 + C3 6 A6 B6 A5 * B5 C5 A4 * B4 + C4 7 A7 B7 A6 * B6 C6 A5 * B5 + C5 8 A7 * B7 C7 A6 * B6 + C6 9 A7 * B7 + C7 Pipelining
  • 15. 15 Pipelining and Vector Processing Computer Organization Computer Architectures Lab GENERAL PIPELINE General Structure of a 4-Segment Pipeline S R 1 1 S R 2 2 S R 3 3 S R 4 4 Input Clock Space-Time Diagram 1 2 3 4 5 6 7 8 9 T1 T1 T1 T1 T2 T2 T2 T2 T3 T3 T3 T3 T4 T4 T4 T4 T5 T5 T5 T5 T6 T6 T6 T6 Clock cycles Segment 1 2 3 4 Pipelining
  • 16. 16 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PIPELINE SPEEDUP n: Number of tasks to be performed Conventional Machine (Non-Pipelined) tn: Clock cycle t1: Time required to complete the n tasks t1 = n * tn Pipelined Machine (k stages) tp: Clock cycle (time to complete each suboperation) tk: Time required to complete the n tasks tk = (k + n - 1) * tp Speedup Sk: Speedup Sk = n*tn / (k + n - 1)*tp n   Sk = tn tp ( = k, if tn = k * tp ) lim Pipelining
  • 17. 17 Pipelining and Vector Processing Computer Organization Computer Architectures Lab PIPELINE AND MULTIPLE FUNCTION UNITS P1 I i P2 Ii+1 P3 I i+2 P4 I i+3 Multiple Functional Units Example - 4-stage pipeline - subopertion in each stage; tp = 20nS - 100 tasks to be executed - 1 task in non-pipelined system; 20*4 = 80nS Pipelined System (k + n - 1)*tp = (4 + 99) * 20 = 2060nS Non-Pipelined System n*k*tp = 100 * 80 = 8000nS Speedup Sk = 8000 / 2060 = 3.88 4-Stage Pipeline is basically identical to the system with 4 identical function units Pipelining
  • 18. 18 Pipelining and Vector Processing Computer Organization Computer Architectures Lab ARITHMETIC PIPELINE Floating-point adder [1] Compare the exponents [2] Align the mantissa [3] Add/sub the mantissa [4] Normalize the result X = A x 2a Y = B x 2b R Compare exponents by subtraction a b R Choose exponent Exponents R A B Align mantissa Mantissas Difference R Add or subtract mantissas R Normalize result R R Adjust exponent R Segment 1: Segment 2: Segment 3: Segment 4: Arithmetic Pipeline
  • 19. 19 Pipelining and Vector Processing Computer Organization Computer Architectures Lab 4-STAGE FLOATING POINT ADDER A = a x 2p B = b x 2q p a q b Exponent subtractor Fraction selector Fraction with min(p,q) Right shifter Other fraction t = |p - q| r = max(p,q) Fraction adder Leading zero counter r c Left shifter c Exponent adder r s d d Stages: S1 S2 S3 S4 C = A + B = c x 2 = d x 2 r s (r = max (p,q), 0.5  d < 1) Arithmetic Pipeline
  • 20. 20 Pipelining and Vector Processing Computer Organization Computer Architectures Lab INSTRUCTION CYCLE Six Phases* in an Instruction Cycle [1] Fetch an instruction from memory [2] Decode the instruction [3] Calculate the effective address of the operand [4] Fetch the operands from memory [5] Execute the operation [6] Store the result in the proper place * Some instructions skip some phases * Effective address calculation can be done in the part of the decoding phase * Storage of the operation result into a register is done automatically in the execution phase ==> 4-Stage Pipeline [1] FI: Fetch an instruction from memory [2] DA: Decode the instruction and calculate the effective address of the operand [3] FO: Fetch the operand [4] EX: Execute the operation Instruction Pipeline
  • 21. 21 Pipelining and Vector Processing Computer Organization Computer Architectures Lab INSTRUCTION PIPELINE Execution of Three Instructions in a 4-Stage Pipeline Instruction Pipeline FI DA FO EX FI DA FO EX FI DA FO EX i i+1 i+2 Conventional Pipelined FI DA FO EX FI DA FO EX FI DA FO EX i i+1 i+2
  • 22. 22 Pipelining and Vector Processing Computer Organization Computer Architectures Lab INSTRUCTION EXECUTION IN A 4-STAGE PIPELINE 1 2 3 4 5 6 7 8 9 10 12 13 11 FI DA FO EX 1 FI DA FO EX FI DA FO EX FI DA FO EX FI DA FO EX FI DA FO EX FI DA FO EX 2 3 4 5 6 7 FI Step: Instruction (Branch) Instruction Pipeline Fetch instruction from memory Decode instruction and calculate effective address Branch? Fetch operand from memory Execute instruction Interrupt? Interrupt handling Update PC Empty pipe no yes yes no Segment1: Segment2: Segment3: Segment4:
  • 23. 23 Pipelining and Vector Processing Computer Organization Computer Architectures Lab MAJOR HAZARDS IN PIPELINED EXECUTION Structural hazards(Resource Conflicts) Hardware Resources required by the instructions in simultaneous overlapped execution cannot be met Data hazards (Data Dependency Conflicts) An instruction scheduled to be executed in the pipeline requires the result of a previous instruction, which is not yet available JMP ID PC + PC bubble IF ID OF OE OS Branch address dependency Hazards in pipelines may make it necessary to stall the pipeline Pipeline Interlock: Detect Hazards Stall until it is cleared Instruction Pipeline ADD DA B,C + INC DA +1 R1 bubble Data dependency R1 <- B + C R1 <- R1 + 1 Control hazards Branches and other instructions that change the PC make the fetch of the next instruction to be delayed
  • 24. 24 Pipelining and Vector Processing Computer Organization Computer Architectures Lab STRUCTURAL HAZARDS Structural Hazards Occur when some resource has not been duplicated enough to allow all combinations of instructions in the pipeline to execute Example: With one memory-port, a data and an instruction fetch cannot be initiated in the same clock The Pipeline is stalled for a structural hazard <- Two Loads with one port memory -> Two-port memory will serve without stall Instruction Pipeline FI DA FO EX i i+1 i+2 FI DA FO EX FI DA FO EX stall stall
  • 25. 25 Pipelining and Vector Processing Computer Organization Computer Architectures Lab DATA HAZARDS Data Hazards Occurs when the execution of an instruction depends on the results of a previous instruction ADD R1, R2, R3 SUB R4, R1, R5 Hardware Technique Interlock - hardware detects the data dependencies and delays the scheduling of the dependent instruction by stalling enough clock cycles Forwarding (bypassing, short-circuiting) - Accomplished by a data path that routes a value from a source (usually an ALU) to a user, bypassing a designated register. This allows the value to be produced to be used at an earlier stage in the pipeline than would otherwise be possible Software Technique Instruction Scheduling(compiler) for delayed load Data hazard can be dealt with either hardware techniques or software technique Instruction Pipeline
  • 26. 26 Pipelining and Vector Processing Computer Organization Computer Architectures Lab FORWARDING HARDWARE Register file Result write bus Bypass path ALU result buffer MUX ALU R4 MUX Instruction Pipeline Example: ADD R1, R2, R3 SUB R4, R1, R5 3-stage Pipeline I: Instruction Fetch A: Decode, Read Registers, ALU Operations E: Write the result to the destination register I A E ADD SUB I A E Without Bypassing I A E SUB With Bypassing
  • 27. 27 Pipelining and Vector Processing Computer Organization Computer Architectures Lab INSTRUCTION SCHEDULING a = b + c; d = e - f; Unscheduled code: Delayed Load A load requiring that the following instruction not use its result Scheduled Code: LW Rb, b LW Rc, c LW Re, e ADD Ra, Rb, Rc LW Rf, f SW a, Ra SUB Rd, Re, Rf SW d, Rd LW Rb, b LW Rc, c ADD Ra, Rb, Rc SW a, Ra LW Re, e LW Rf, f SUB Rd, Re, Rf SW d, Rd Instruction Pipeline
  • 28. 28 Pipelining and Vector Processing Computer Organization Computer Architectures Lab CONTROL HAZARDS Branch Instructions - Branch target address is not known until the branch instruction is completed - Stall -> waste of cycle times FI DA FO EX FI DA FO EX Branch Instruction Next Instruction Target address available Dealing with Control Hazards * Prefetch Target Instruction * Branch Target Buffer * Loop Buffer * Branch Prediction * Delayed Branch Instruction Pipeline
  • 29. 29 Pipelining and Vector Processing Computer Organization Computer Architectures Lab CONTROL HAZARDS Instruction Pipeline Prefetch Target Instruction – Fetch instructions in both streams, branch not taken and branch taken – Both are saved until branch branch is executed. Then, select the right instruction stream and discard the wrong stream Branch Target Buffer(BTB; Associative Memory) – Entry: Addr of previously executed branches; Target instruction and the next few instructions – When fetching an instruction, search BTB. – If found, fetch the instruction stream in BTB; – If not, new stream is fetched and update BTB Loop Buffer(High Speed Register file) – Storage of entire loop that allows to execute a loop without accessing memory Branch Prediction – Guessing the branch condition, and fetch an instruction stream based on the guess. Correct guess eliminates the branch penalty Delayed Branch – Compiler detects the branch and rearranges the instruction sequence by inserting useful instructions that keep the pipeline busy in the presence of a branch instruction
  • 30. 30 Pipelining and Vector Processing Computer Organization Computer Architectures Lab RISC PIPELINE Instruction Cycles of Three-Stage Instruction Pipeline RISC Pipeline RISC - Machine with a very fast clock cycle that executes at the rate of one instruction per cycle <- Simple Instruction Set Fixed Length Instruction Format Register-to-Register Operations Data Manipulation Instructions I: Instruction Fetch A: Decode, Read Registers, ALU Operations E: Write a Register Load and Store Instructions I: Instruction Fetch A: Decode, Evaluate Effective Address E: Register-to-Memory or Memory-to-Register Program Control Instructions I: Instruction Fetch A: Decode, Evaluate Branch Address E: Write Register(PC)
  • 31. 31 Pipelining and Vector Processing Computer Organization Computer Architectures Lab DELAYED LOAD Three-segment pipeline timing Pipeline timing with data conflict clock cycle 1 2 3 4 5 6 Load R1 I A E Load R2 I A E Add R1+R2 I A E Store R3 I A E Pipeline timing with delayed load clock cycle 1 2 3 4 5 6 7 Load R1 I A E Load R2 I A E NOP I A E Add R1+R2 I A E Store R3 I A E LOAD: R1  M[address 1] LOAD: R2  M[address 2] ADD: R3  R1 + R2 STORE: M[address 3]  R3 RISC Pipeline The data dependency is taken care by the compiler rather than the hardware
  • 32. 32 Pipelining and Vector Processing Computer Organization Computer Architectures Lab DELAYED BRANCH 1 I 3 4 6 5 2 Clock cycles: 1. Load A 2. Increment 4. Subtract 5. Branch to X 7 3. Add 8 6. NOP E I A E I A E I A E I A E I A E 9 10 7. NOP 8. Instr. in X I A E I A E 1 I 3 4 6 5 2 Clock cycles: 1. Load A 2. Increment 4. Add 5. Subtract 7 3. Branch to X 8 6. Instr. in X E I A E I A E I A E I A E I A E Compiler analyzes the instructions before and after the branch and rearranges the program sequence by inserting useful instructions in the delay steps Using no-operation instructions Rearranging the instructions RISC Pipeline
  • 33. 33 Pipelining and Vector Processing Computer Organization Computer Architectures Lab VECTOR PROCESSING Vector Processing Vector Processing Applications • Problems that can be efficiently formulated in terms of vectors – Long-range weather forecasting – Petroleum explorations – Seismic data analysis – Medical diagnosis – Aerodynamics and space flight simulations – Artificial intelligence and expert systems – Mapping the human genome – Image processing Vector Processor (computer) Ability to process vectors, and related data structures such as matrices and multi-dimensional arrays, much faster than conventional computers Vector Processors may also be pipelined
  • 34. 34 Pipelining and Vector Processing Computer Organization Computer Architectures Lab VECTOR PROGRAMMING DO 20 I = 1, 100 20 C(I) = B(I) + A(I) Conventional computer Initialize I = 0 20 Read A(I) Read B(I) Store C(I) = A(I) + B(I) Increment I = i + 1 If I  100 goto 20 Vector computer C(1:100) = A(1:100) + B(1:100) Vector Processing
  • 35. 35 Pipelining and Vector Processing Computer Organization Computer Architectures Lab VECTOR INSTRUCTIONS f1: V * V f2: V * S f3: V x V * V f4: V x S * V V: Vector operand S: Scalar operand Type Mnemonic Description (I = 1, ..., n) Vector Processing f1 VSQR Vector square root B(I) * SQR(A(I)) VSIN Vector sine B(I) * sin(A(I)) VCOM Vector complement A(I) * A(I) f2 VSUM Vector summation S * S A(I) VMAX Vector maximum S * max{A(I)} f3 VADD Vector add C(I) * A(I) + B(I) VMPY Vector multiply C(I) * A(I) * B(I) VAND Vector AND C(I) * A(I) . B(I) VLAR Vector larger C(I) * max(A(I),B(I)) VTGE Vector test > C(I) * 0 if A(I) < B(I) C(I) * 1 if A(I) > B(I) f4 SADD Vector-scalar add B(I) * S + A(I) SDIV Vector-scalar divide B(I) * A(I) / S
  • 36. 36 Pipelining and Vector Processing Computer Organization Computer Architectures Lab VECTOR INSTRUCTION FORMAT Operation code Base address source 1 Base address source 2 Base address destination Vector length Vector Processing Vector Instruction Format Source A Source B Multiplier pipeline Adder pipeline Pipeline for Inner Product
  • 37. 37 Pipelining and Vector Processing Computer Organization Computer Architectures Lab MULTIPLE MEMORY MODULE AND INTERLEAVING Vector Processing Multiple Module Memory Address Interleaving Different sets of addresses are assigned to different memory modules AR Memory array DR AR Memory array DR AR Memory array DR AR Memory array DR Address bus Data bus M0 M1 M2 M3