Pipelining Principles

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Pipelining Principles

• Prof. Sirer
• CS 316
• Cornell University

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Meet the Cast

• Alice

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Meet the Cast

• Alice
• Bob

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Meet the Cast

• Alice
• Bob
• They dont like each other!

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The Laundry

• Four sequential tasks

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Laundry Room Design 1

• A large room with a one entry-door and one
  exit-door

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Laundry Room Design 1

• First Alice owns the room

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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

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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
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Laundry Room Design 2

• Elapsed Time for Alice 4
• Elapsed Time for Bob 4
• Elapsed Time for both 5!!!

Time
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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

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Laundry Room Design 2
Alice
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Laundry Room Design 2
Bob
Alice
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Laundry Room Design 2
Charlie
Bob
Alice
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Laundry Room Design 2
Charlie
Dave
Bob
Alice
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Implications

• Principle Latencies can be masked by running
  isolated operations in parallel
• Need mechanisms for isolation
• Need mechanisms for handling dependencies between
  tasks
• Lets apply this principle to processor design

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MIPS Processor

• Functional decomposition of our processor

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A MIPS Pipeline

• Pipeline stages for a MIPS processor

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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

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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

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Pipelining for Other Circuits

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