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Performance Evaluation of Cache Replacement Policies for the SPEC CPU2000 Benchmark Suite. Hussein Al-Zoubi. Overview. Introduction Common cache replacement policies Experimental methodology Evaluating cache replacement policies: questions and answers Conclusion. Introduction.

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Performance Evaluation of Cache Replacement Policies for the SPEC CPU2000 Benchmark Suite


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performance evaluation of cache replacement policies for the spec cpu2000 benchmark suite

Performance Evaluation of Cache Replacement Policies for the SPEC CPU2000 Benchmark Suite

Hussein Al-Zoubi

overview
Overview
  • Introduction
  • Common cache replacement policies
  • Experimental methodology
  • Evaluating cache replacement policies: questions and answers
  • Conclusion
introduction
Introduction
  • Increasing speed gap between processor and memory
  • Modern processors include multiple levels of caches, cache associativity increases
  • Replacement policy: Which block to discard when the cache is full
introduction cont
Introduction...cont.
  • Optimal Replacement (OPT) algorithm: replace cache memory block whose next reference farthest away in the future, infeasible
  • State-of-the-art processors employ various policies
introduction cont5
Introduction...cont.
  • Random
  • LRU (Least Recently Used)
  • Round-robin (FIFO – First-In-First-Out)
  • PLRU (Pseudo Least Recently Used) : reduce the hardware cost by approximating the LRU mechanism
introduction cont6
Introduction...cont.
  • Our goal: explore and evaluate common cache replacement policies
  • how existing policies relate to OPT
  • effect on instruction and data caches
  • how good are pseudo techniques in approximating true LRU
common cache replacement policies cont
Common cache replacement policies…cont.
  • Random policy: simpler, but at the expense performance. Linear Feedback Shift Register (LFSR)
  • Round Robin (or FIFO) replacement: replacing oldest block in cache memory. Circular counter
experimental methodology
Experimental methodology
  • sim-cache and sim-cheetah simulators
  • Alpha version of the SimpleScalar
  • original simulators modified to support additional pseudo-LRU replacement policies
  • sim-cache simulator modified to print interval statistics per specified number of instructions
evaluating cache replacement policies questions and answers
Evaluating cache replacement policies: questions and answers
  • Q: How much associativity is enough for state-of-the-art benchmarks?
  • A: For data cache, performance gain for transition from a direct mapped to a two-way set associative cache
  • For instruction cache, OPT replacement policy benefits from increased associativity. realistic policies don’t exploit more than 8 ways, or in some cases even more than 2 ways
evaluating cache replacement policies questions and answers cont
Evaluating cache replacement policies: questions and answers…cont.
  • Q: How much space is there for improvement for each specific benchmark and cache configuration?
evaluating cache replacement policies questions and answers cont14
Evaluating cache replacement policies: questions and answers…cont.
  • Q: Do replacement policies behave differently for different types of memory references, such as instruction and data?
  • A: In general, LRU policy has better performance than FIFO and Random with some exceptions
evaluating cache replacement policies questions and answers cont15
Evaluating cache replacement policies: questions and answers…cont.
  • Q: Can dynamic change of replacement policy reduce the total number of cache misses?
  • A: If one policy better than the other, it stays consistently better
evaluating cache replacement policies questions and answers cont16
Evaluating cache replacement policies: questions and answers…cont.
  • Can we use most recently used information for cache way prediction?
evaluating cache replacement policies questions and answers cont17
Evaluating cache replacement policies: questions and answers…cont.
  • Q: How good are pseudo LRU techniques at approximating true LRU?
  • A: PLRUm and PLRUt very efficient in approximating LRU policy and close to LRU during whole program execution
conclusion
Conclusion
  • Eliminating cache misses extremely important for improving overall processor performance
  • Cache replacement policies gain more significance in set associative caches
  • Gap between LRU and OPT replacement policies, up to 50%, new research to close the gap is necessary