6-CachesI - ECE 485/585 Microprocessor System Design Prof....

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ECE 485/585 Microprocessor System Design Prof. Mark G. Faust Maseeh College of Engineering and Computer Science
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ectures Lectures Handouts: Hall • Topics – Caches emory vs Processor Performance • Memory vs. Processor Performance • The Memory Hierarchy – Registers, SRAM, DRAM, Disk patial and Temporal Locality • Spatial and Temporal Locality • Cache Hits and Misses • Direct Mapped Caches wo ay Four ay Caches • Two-Way, Four-Way Caches • Fully Associative (N-Way) Caches • Cache Line Replacement Algorithms • Write Policies • Cache Coherence • Intel Cache Evolution
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emory Technology Trends Memory Technology Trends From Hennessy & Patterson, Computer Architecture: A Quantitative Approach (4 th edition)
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elative Performance Gains Relative Performance Gains 10,000 100,000 Performance 1,000 CPU 10 100 Memory Year 1
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rocessor/Memory Gap Processor/Memory Gap
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Computer Memory Hierarchy Processor Control Secondary Storage (Disk) R Main Memory Second evel O Tertiary Storage (Tape) Third Level h Datapath egisters (DRAM) Level Cache (SRAM) n-Chip Cache Cache (SRAM) Archive Backup File System Paging Instructions Data [Cached Files] Cached DRAM Intermediate results From Hennessy & Patterson, Computer Architecture: A Quantitative Approach (4 th edition)
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tel Pentium 4 3 2 GHz Server Component Access Speed Intel Pentium 4 3.2 GHz Server (Time for data to be returned) Registers 1 cycle = 0.3 nanoseconds L1 Cache 3 cycles = nanoseconds 1 nanoseconds L2 Cache 20 cycles = 7 nanoseconds L3 Cache 40 cycles = 13 nanoseconds emory 00 cycles = Memory 300 cycles 100 nanoseconds
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ow is the Hierarchy Managed? How is the Hierarchy Managed? • Registers ÅÆ Memory – Compiler – Programmer • Cache ÅÆ Memory – Hardware • Memory ÅÆ Disk – Operating System (Virtual Memory: Paging) – Programmer (File System)
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rinciple of Locality Principle of Locality • Makes it possible for a cache to provide an improvement in performance • Temporal Locality – A referenced item is likely to be referenced again soon ode example: a function or loop Code example: a function or loop • Data example: commonly used variables, pointers • Spatial Locality – Nearby items are likely to be referenced soon • Code example: most likely place for next instruction is IP+1 • Data example: arrays
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aching – tudent Advising Analogy Caching Student Advising Analogy housands of student folders Thousands of student folders Indexed by 9-digit student ID Located down the hall – long walk Space for 100 file folders at my desk ocated at my side ort access time Located at my side – short access time
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Cache Hits and Misses •H i t – Desired item is in the cache Miss – Desired item is not in the cache – Request from next level in storage hierarchy it R t Hit Rate – Probability an item is in the cache Hit Time ime to deliver the item if it’s in the cache Time to deliver the item if it s in the cache • Determine hit/miss, access cache Miss Rate robability an item isn’t in the cache (1- it Rate)
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This note was uploaded on 02/01/2010 for the course ECE 585 taught by Professor Faust during the Fall '08 term at Portland State.

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6-CachesI - ECE 485/585 Microprocessor System Design Prof....

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