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Hyper-Threading & Related Concepts

Hyper-Threading & Related Concepts. Yu Fu. Content. Conventional multithreading Out-of-order execution (OOE) SSSSSSSS Symmetric multiprocessing (SMP) Simultaneous multithreading (SMT) Hyper-threading Implementation ssssssssssssssssssssss. Conventional multithreading. Front End

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Hyper-Threading & Related Concepts

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  1. Hyper-Threading & Related Concepts Yu Fu

  2. Content • Conventional multithreading • Out-of-order execution (OOE)SSSSSSSS • Symmetric multiprocessing (SMP) • Simultaneous multithreading (SMT) • Hyper-threading • Implementation ssssssssssssssssssssss

  3. Conventional multithreading Front End Execution Core

  4. Out-of-order Executiondata dependency • RAW (read after write) i1. R2  R1 + R3 i2. R4  R2 + R3 • WAR (write after write) i1. R1  R2 + R3 i2. R3  R4 * R5 • WAW (write after write) i1. R2  R1 + R3 i2. R2  R4 * R7

  5. Out-of-order ExecutionTomasulo’s Algorithm • Register renaming • WAR i1. R1  R2 + R3_a i2. R3_b  R4 * R5 • WAW i1. R2_a  R1 + R3 i2. R2_b  R4 * R7 • Reservation station • RAW

  6. Out-of-order ExecutionLimitation • Available Registers • RAW - true data dependency • Branch Prediction • Memory Address Aliases

  7. Symmetric multiprocessing (SMP) • Two single-threaded processors • Double execution time as well as the waste

  8. Simultaneous multithreading (SMT) • Threads from different programs in a single time slice • Only one thread in each clock cycle

  9. Hyper-threadingCompared with SMT Hyper-threading SMT

  10. Hyper-threadingCompare with SMP Logical Processors Hyper-threading SMP

  11. Hyper-threadingImplementation • Replicated Resources • Partitioned Resources • Shared Resources • Problemsssssssssssssssssssssssssssssss

  12. Hyper-threadingImplementation problems caused by sharing resources • Logical processors require same function units in Execution Core • One logical processor may monopolize shared resources • Not enough cache causes thrashing

  13. The End Thank You !

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