Page 22 - Multipath MIPS

Simultaneous Multithreading (SMT)

 Combines multithreading with superscalar techniques

 Several hardware contexts and register sets
 Issuing instructions from several threads simultaneously
 Can exploit TLP and ILP

 Resource Sharing (min H.W. Vertical/Horizontal Waste
Complexity): instructions of
1 1234
different threads share most of the Time (Processor cycles)
resources [Alpha 21464] Thread1111 111 1
1 222
 Resource Replication (higher H.W Time (Processor cycles) Threads 3
overhead): most buffers and 1111 33 3
442 3
resources are replicated/statically 1111 411 4
bound to threads [Multithreaded Issue Slots 123
Superscalar Processor].
Issue Slots
 Issue how many? From which?

 Commercial SMT (all 2-way)
 Intel HT P4/Nehalem
 IBM Power5, Power6

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