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Pipelining Principles

Prof. Sirer CS 316 Cornell University. Pipelining Principles. Meet the Cast. Alice. Meet the Cast. Alice Bob. Meet the Cast. Alice Bob They don’t like each other!. The Laundry. Four sequential tasks. Laundry Room Design #1. A large room with a one entry-door and one exit-door.

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Pipelining Principles

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  1. Prof. Sirer CS 316 Cornell University Pipelining Principles

  2. Meet the Cast • Alice

  3. Meet the Cast • Alice • Bob

  4. Meet the Cast • Alice • Bob • They don’t like each other!

  5. The Laundry • Four sequential tasks

  6. Laundry Room Design #1 • A large room with a one entry-door and one exit-door

  7. Laundry Room Design #1 • First Alice owns the room

  8. Laundry Room Design #1 • First Alice owns the room • Bob can enter as soon as she is done • No possibility for Alice and Bob to fight

  9. Laundry Room Design #1 • Elapsed Time for Alice: 4 • Elapsed Time for Bob: 4 • Elapsed Time for both: 8 • A better laundry room can improve utilization and speed up task completion Time

  10. Laundry Room Design #2 • Elapsed Time for Alice: 4 • Elapsed Time for Bob: 4 • Elapsed Time for both: 5!!! Time

  11. Laundry Room Design #2 • The room is partitioned into stages • One person owns a stage at a time, the room can hold up to four people simultaneously

  12. Laundry Room Design #2 Alice

  13. Laundry Room Design #2 Bob Alice

  14. Laundry Room Design #2 Charlie Bob Alice

  15. Laundry Room Design #2 Dave Charlie Bob Alice

  16. Implications • Principle: Latencies can be masked by running isolated operations in parallel • Need mechanisms for isolation • Need mechanisms for handling dependencies between tasks • Let’s apply this principle to processor design…

  17. MIPS Processor • Functional decomposition of our processor

  18. A MIPS Pipeline • Pipeline stages for a MIPS processor

  19. Pipeline Isolation • Latches between pipeline stages hold the values for the stage to operate on • Latches and register file are triggered on opposite edges of the clock

  20. Pipeline Logic • Additional latches required to store the instruction for each pipeline stage • Copy the instruction forward, generate local control signals separately in each pipeline stage

  21. Pipelining for Other Circuits • Pipelining can be applied to any combinational logic circuit • What’s the circuit latency at 2ns. per gate? • What’s the throughput? • What is the stage breakdown? Where would you place latches? • What’s the throughput after pipelining? • Pipelining vs. superpipelining

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