lect05-superscalar-org

lect05-superscalar-org - Limitations of Scalar Pipelines...

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ECE/CS 752:Advanced Computer Architecture I 1 Superscalar Organization Prof. Mikko H. Lipasti University of Wisconsin Madison Lecture notes based on notes by John P. Shen Updated by Mikko Lipasti Limitations of Scalar Pipelines Scalar upper bound on throughput –IPC <= 1 or CPI >= 1 Inefficient unified pipeline –Long latency for each instruction Rigid pipeline stall policy – One stalled instruction stalls all newer instructions Parallel Pipelines (a) No Parallelism (b) Temporal Parallelism (c) Spatial Parallelism (d) Parallel Pipeline Spatial Pipeline Unrolling Pipeline Unrolling - Power 12-stage pipeline, 60% latch power, 25% latch delay+setup, 12% area on latches, 20% leakage power © Shen, Lipasti 5 0 0.2 0.4 0.6 0.8 1 1.2 0 2 4 6 8 10 12 1x12s 2x6s 3x4s 4x3s 6x2s 12x1s Relative Power Relative Area Pipeline Configuration Relative Area and Power vs. Pipeline Configuration Dynamic Static Total area ec Intel Pentium Parallel Pipeline IF D1 D2 EX WB IF IF D1 D1 D2 D2 EX EX WB WB U - Pipe V - Pipe
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ECE/CS 752:Advanced Computer Architecture I 2 Diversified Pipelines •• • IF ID RD WB ALU MEM1 FP1 BR MEM2 FP2 FP3 EX Power4 Diversified Pipelines PC I-Cache BR Scan BR Predict Fetch Q Decode Reorder Buffer BR/CR Issue Q CR Unit BR Unit FX/LD 1 Issue Q FX1 Unit LD1 Unit FX/LD 2 Issue Q LD2 Unit FX2 Unit FP Issue Q FP1 Unit FP2 Unit StQ D-Cache Rigid Pipeline Stall Policy Bypassing of Stalled Instruction Stalled Instruction Backward Propagation of Stalling Not Allowed Dynamic Pipelines IF ID RD WB ALU MEM1 FP1 BR MEM2 FP2 FP3 EX Dispatch Buffer Reorder Buffer ( in order ) ( out of order ) ( out of order ) ( in order ) Interstage Buffers ••• Stage i Buffer (n) Stage i +1 Stage i Buffer (> n) Stage i + 1 n n Stage i Buffer (1) Stage i + 1 (a) (b) (c) ( in order ) ( out of order ) _ ( in order ) 1 1 ( in order ) Superscalar Pipeline Stages Instruction Buffer Fetch Dispatch Buffer Decode Issuing Buffer Dispatch Completion Buffer Execute Store Buffer Complete Retire In Program Order In Program Order Out of Order
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ECE/CS 752:Advanced Computer Architecture I 3 Limitations of Scalar Pipelines
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lect05-superscalar-org - Limitations of Scalar Pipelines...

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