Computer Organization and Architecture | Pipelining | Set 3 (Types and Stalling)

Please see Set 1 for Execution, Stages and Performance (Throughput) and Set 2 for Dependencies and Data Hazard.
Types of pipeline

  • Uniform delay pipeline
    In this type of pipeline, all the stages will take same time to complete an operation.
    In uniform delay pipeline, Cycle Time (Tp) = Stage Delay

    If buffers are included between the stages then, Cycle Time (Tp) = Stage Delay + Buffer Delay


  • Non-Uniform delay pipeline
    In this type of pipeline, different stages take different time to complete an operation.
    In this type of pipeline, Cycle Time (Tp) = Maximum(Stage Delay)

    For example, if there are 4 stages with delays, 1 ns, 2 ns, 3 ns, and 4 ns, then

    Tp = Maximum(1 ns, 2 ns, 3 ns, 4 ns) = 4 ns

    If buffers are included between the stages,

    Tp = Maximum(Stage delay + Buffer delay)

    Example : Consider a 4 segment pipeline with stage delays (2 ns, 8 ns, 3 ns, 10 ns). Find the time taken to execute 100 tasks in the above pipeline.
    Solution : As the above pipeline is a non-linear pipeline,
    Tp = max(2, 8, 3, 10) = 10 ns
    We know that ETpipeline = (k + n – 1) Tp = (4 + 100 – 1) 10 ns = 1030 ns

    NOTE: MIPS = Million instructions per second


Performance of pipeline with stalls

Speed Up (S) = Performancepipeline / Performancenon-pipeline
=> S = Average Execution Timenon-pipeline / Average Execution Timepipeline
=> S = CPInon-pipeline * Cycle Timenon-pipeline / CPIpipeline * Cycle Timepipeline

Ideal CPI of the pipelined processor is ‘1’. But due to stalls, it becomes greater than ‘1’.

S = CPInon-pipeline * Cycle Timenon-pipeline  / (1 + Number of stalls per Instruction) * Cycle Timepipeline

As Cycle Timenon-pipeline =   Cycle Timepipeline,

Speed Up (S) = CPInon-pipeline / (1 + Number of stalls per instruction) 

Sources :
This article has been contributed by Saurabh Sharma.
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