Data value prediction - PowerPoint PPT Presentation

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Data value prediction

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Data value prediction Bas van der Tol Limits to ILP Instruction Level Parallelism is limited by Control flow Data flow: true dependencies Types of Speculative ... – PowerPoint PPT presentation

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Title: Data value prediction


1
Data value prediction
  • Bas van der Tol

2
Limits to ILP
  • Instruction Level Parallelism is limited by
  • Control flow
  • Data flow true dependencies

3
Types of Speculative Execution
4
Sources of predicatable data
  • Data redundancy
  • Error-checking
  • Program constants
  • Virtual function calls
  • Glue code
  • Call-subgraph identities
  • Register spill code

5
Register value locality
6
Value Prediction Unit
7
VPT Hit rate sensitivity to Size
8
Example use of Value Prediction
9
Penalties
Penalties
  • Misprediction penalty
  • Structural hazards, both on correct and
    mispredictions

10
Configurations used for experiments
11
PowerPC 620 Speedup
12
PowerPC 620 Speedup
13
Infinite Machine Model Speedup
14
Data cache vs. Value Prediction
15
Improving Prediction Accuracy
  • Last Value Prediction
  • Stride Prediction
  • Finite Context Method Predictors (fcm)

16
Finite Context Models
17
Prediction Success
18
Conclusions
  • Data value prediction increases performance by 5
    on PowerPC 620
  • A performance gain of 23 is possible
  • Future Developments
  • More parallel execution units
  • Better prediction models
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