Question

A bne instruction can result in a specific kind of hazard. (a) What is this kind of hazard called? (b) How can such hazard be solved? (c) For deep pipelines, such hazards can have very negative impact on the performance. Explain why (d) Which technique is used in modern processors to remedy this negative impact? Mo- tivate why this is the case.

Answer c) and d)

Answer 1

C).Bne instructions are like jump instructions.In pipelining new inputs are inserted into pipelining every nee cycle to get CPI of 1.due to this property jump instructions creates control hazards.hazards are nothing but delay or stall i.e. cycle without new inputs into pipeline.

Let's take example to understand what problems occurs in jump instructions:-

Consider a 5 stage pipeline in RISC architecture

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D)to solve control hazards there are various methods like

1.Hardware techniques:-(branch prediction buffers)

2.Software techniques:-(delayed branch and NOP subsitution)

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