Lecture_18 - Chapter 5 Large and Fast: Exploiting Memory...

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Chapter 5 Large and Fast: Exploiting Memory Hierarchy
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Chapter 5 — Large and Fast: Exploiting Memory Hierarchy — 2 Associative Caches Fully associative Allow a given block to go in any cache entry Requires all entries to be searched at once Comparator per entry (expensive) n -way set associative Each set contains n entries Block number determines which set (Block number) modulo (#Sets in cache) Search all entries in a given set at once n comparators (less expensive)
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Chapter 5 — Large and Fast: Exploiting Memory Hierarchy — 3 Associative Cache Example
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Chapter 5 — Large and Fast: Exploiting Memory Hierarchy — 4 Spectrum of Associativity For a cache with 8 entries
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Chapter 5 — Large and Fast: Exploiting Memory Hierarchy — 5 Associativity Example Compare 4-block caches Direct mapped, 2-way set associative, fully associative Block access sequence: 0, 8, 0, 6, 8 Direct mapped Block address Cache index Hit/miss Cache content after access 0 1 2 3 0 0 miss Mem[0] 8 0 miss Mem[8] 0 0 miss Mem[0] 6 2 miss Mem[0] Mem[6] 8 0 miss Mem[8] Mem[6]
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Chapter 5 — Large and Fast: Exploiting Memory Hierarchy — 6 Associativity Example 2-way set associative Block address Cache index Hit/miss Cache content after access Set 0 Set 1 0 0 miss Mem[0] 8 0 miss Mem[0] Mem[8] 0 0 hit Mem[0] Mem[8] 6 0 miss Mem[0] Mem[6] 8 0 miss Mem[8] Mem[6] Fully associative Block address Hit/miss Cache content after access 0 miss Mem[0] 8 miss Mem[0] Mem[8] 0 hit Mem[0] Mem[8] 6 miss Mem[0] Mem[8] Mem[6] 8 hit Mem[0] Mem[8] Mem[6]
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Chapter 5 — Large and Fast: Exploiting Memory Hierarchy — 7 How Much Associativity Increased associativity decreases miss rate But with diminishing returns Simulation of a system with 64KB D-cache, 16-word blocks, SPEC2000 1-way: 10.3% 2-way: 8.6% 4-way: 8.3% 8-way: 8.1%
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Chapter 5 — Large and Fast: Exploiting Memory Hierarchy — 8 Set Associative Cache Organization
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Replacement Policy Direct mapped: no choice Set associative
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Lecture_18 - Chapter 5 Large and Fast: Exploiting Memory...

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