Cache Replacement in Modern Processors

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Cache Replacement in Modern Processors

• Prepared By
• Paul Kosinski and Bridget Johnston

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Introduction

• The replacement policy specifies which disk block
  should be removed when a new block must be
  entered into an already full cache, and should be
  chosen so as to ensure that blocks likely to be
  referenced in the near future are retained in the
  cache.

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Common Cache Replacement Policies Used

• Least Recently Used (LRU)
• First In First Out (FIFO)
• Last In First Out (LIFO)
• Random (Rand)

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Least Recently Used

• Replaces the block in the cache which has not
  been used for the longest period of time
• Advantage simplicity
• Drawback does not consider file sizes latency

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First In First Out

• Determines the oldest block rather than the least
  recently used.
• Advantage Easier to calculate

Last In First Out

• Uses the newest block

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Random

• Candidate blocks are randomly selected.
• All disk blocks are accessed with equal
  probability
• Used as a benchmark

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Problem Statement

• We will show the Cache Replacement Policy used by
  the Pentium III and Pentium IV processors and
  propose why each policy was used. We will use a
  simple matrix multiplication program and Vtune to
  determine our results.

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Experimental Setup

• Matrix Multiplication program
• Vtune
• Intel Pentium III machine
• Intel Pentium IV machine

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Experimental Process

• Ran matrix multiplication program on Pentium III
  IV with the following inputs as the dimensions
  of an n x n matrix

128
256
512
1024
2048
4098
8192
160
320
640
1280
2560
5120
10240
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Intel Pentium III results
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Intel Pentium III results
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Intel Pentium III results
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Intel Pentium III results
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Intel Pentium IV results
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Intel Pentium IV results
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Conclusion

• Results Dont Mean Anything
• Simple Hardware Required due to Timing
  Constraints
• This Means Only Simple Algorithms Should be Used
• LRU
• FIFO