ch7 - CHAPTER 7: DISTRIBUTED SHARED MEMORY DSM simulates a...

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CHAPTER 7: DISTRIBUTED SHARED MEMORY DSM simulates a logical shared memory address space over a set of physically distributed local memory systems. Why DSM? direct information sharing programming paradigm (transparency) multilevel memory access (locality) wealth of existing programs (portability) large physical memory scalable multiprocessor system Chapter outline NUMA architectures: similarity between multiprocessor cache and DSM systems Memory consistency models: why is memory consistency a more crit- ical problem in multiprocessor and DSM systems? how is memory consistency deFned? Cache coherency protocols: implementation of consistency models DSM Implementation: applying the consistency models and coherency protocols to a DSM system 1
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Nonuniform Memory Access (NUMA) architectures Generic NUMA architecture . . . . . . . buses, interconnection network, or communication network controller memory coherence controller memory coherence memory processor memory processor 2
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Multiprocessor Cache and DSM architectures (a) Multiprocessor cache architecture (b) Distributed shared memory architecture Global Memory Common Bus Local Caches Processors Virtual Memory Space Communication Network Local Memory Processors 3
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Common issues Data consistency and coherency due to data placement, migration and repli- cation Data Sharing Granularity Cache Miss Granularity Tradeofs: TransFer time Administrative overhead Hit rate Replacement rate ±alse Sharing What to do on cache miss? Locating block - owner/directory Block Migration - block bouncing Block Replication Push vs. Pull 4
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Memory consistency models These models apply consistency constraints to all memory accesses Accesses may require multiple messages and take signifcant time Atomic consistency All processors see same (global) order Respects real-time order Sequential consistency All processors see same (global) order and order respects all internal orders (not nec. real time) P 1 : W ( X )1
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ch7 - CHAPTER 7: DISTRIBUTED SHARED MEMORY DSM simulates a...

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