Pipelining and Performance Optimization Quiz Quiz

Assess your understanding of pipelining concepts and performance optimization techniques in computer architecture. Explore fundamental ideas such as instruction execution, hazards, throughput, and efficiency gains with this focused multiple-choice quiz.

1. Pipeline Stages

   In a classic 5-stage instruction pipeline, which stage is primarily responsible for decoding the instruction and reading registers?

   1. Instruction Decode (ID)
   2. Instruction Fetch (IF)
   3. Memory Access (MEM)
   4. Execute (EXE)

   Explanation: Instruction Decode (ID) is the stage that decodes the fetched instruction and reads the necessary registers. Instruction Fetch (IF) only retrieves the instruction from memory, not decoding it. Execute (EXE) performs the required computation, while Memory Access (MEM) deals with data memory operations. Only the ID stage is responsible for both decoding and register reading.

2. Pipeline Hazards

   Which type of pipeline hazard occurs when an instruction depends on the result of a previous instruction that has not yet completed, as in 'ADD R1, R2, R3' followed by 'SUB R4, R1, R5'?

   1. Timimg Hazard
   2. Control Hazard
   3. Data Hazard
   4. Structural Hazard

   Explanation: A Data Hazard arises when instructions have a data dependency, such as needing a register value that is yet to be updated. Control Hazards relate to branch decisions, not data. Structural Hazards happen when hardware resources are insufficient. 'Timimg Hazard' is a typographical error and not a standard hazard type.

3. Pipeline Throughput

   Assuming ideal conditions with no hazards, what is the main advantage of instruction pipelining regarding overall CPU throughput?

   1. Increases the number of instructions completed per cycle
   2. Reduces the complexity of individual instructions
   3. Decreases the number of required CPU registers
   4. Lowers the clock frequency

   Explanation: Pipelining allows multiple instructions to overlap in execution, which increases the instruction throughput, or the number of instructions completed per cycle. It does not inherently reduce instruction complexity or the number of CPU registers. Pipelining generally allows higher clock frequencies rather than lowering them.

4. Performance Optimization Techniques

   Which of the following software techniques helps maximize pipeline efficiency by rearranging instructions to minimize pipeline stalls?

   1. Cache Mirroring
   2. Instruction Scheduling
   3. Branch Predictiong
   4. Register Renaming

   Explanation: Instruction Scheduling reorders instructions to minimize data hazards and pipeline stalls, optimizing pipeline flow. Register Renaming helps avoid false dependencies but does not directly reorder code. 'Branch Predictiong' is a misspelling of Branch Prediction, which helps reduce control hazards, not directly rearrange instructions. Cache Mirroring is not a common software optimization for pipelines.

5. Pipeline Performance Metrics

   If a pipeline has an initiation interval of 1 cycle and contains 4 stages, how many cycles will it take to complete 10 instructions, ignoring hazards and stalls?

   1. 7 cycles
   2. 14 cycles
   3. 10 cycles
   4. 13 cycles

   Explanation: With four stages and 10 instructions, the first instruction completes in 4 cycles, and each subsequent instruction completes one cycle later. Thus, it takes 4 (for the pipeline to fill) plus 9 (for the remaining instructions) for a total of 13 cycles. The options '7 cycles' and '10 cycles' underestimate the effect of pipeline filling, and '14 cycles' overestimates the count.